Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Punctuated equilibrium wikipedia , lookup
Evidence of common descent wikipedia , lookup
Paleontology wikipedia , lookup
Hologenome theory of evolution wikipedia , lookup
Evolutionary history of life wikipedia , lookup
The Descent of Man, and Selection in Relation to Sex wikipedia , lookup
Saltation (biology) wikipedia , lookup
Transitional fossil wikipedia , lookup
Unit 3 [NEW PAGE] Evolution [CATCH UO7-P01-OB11USB; Size UO; R; Description of photo to come in addendum photo ms] Overall Expectations ∙ analyze the economic and environmental advantages and disadvantages of an artificial selection technology, and evaluate the impact of environmental changes on natural selection and endangered species ∙ investigate evolutionary processes, and analyze scientific evidence that supports the theory of evolution ∙ demonstrate an understanding of the theory of evolution, the evidence that supports it, and some of the mechanisms by which it occurs Big Ideas ∙ Evolution is the process of biological change over time based on the relationships between species and their environments. ∙ The theory of evolution is a scientific explanation based on a large accumulation of evidence. ∙ Technology that enable humans to manipulate the development of species has economic and environmental implications. UNIT TASK PREVIEW In this Unit Task you will [t/k] [END PAGE] [NEW PAGE] Focus on STSE Title t/k [t/k] QUESTIONS [t/k] 1. 2. 3. [END PAGE] [NEW PAGE – 2 PAGE SPREAD BEGINS; FLOW TEXT OVER SPREAD] [Formatter: format this spread in two columns] Unit 3 Are You Ready? [Formatter: Please format the “Concepts & Skills” in two columns at the top of the page, as per design] CONCEPTS ∙ [t/k] SKILLS MENU ∙ [t/k] Concepts Review 1. 2. 3. Skills Review Career Pathways [t/k] [END 2 PAGE SPREAD] [begin page] Chapter 7 The Theory of Evolution Title [t/k] KEY CONCEPTS In this chapter you will be able to ∙ [t/k in order used in chapter] text t/k ∙ STARTING POINTS Answer the following questions using your current knowledge. You will have an opportunity to revisit these questions later, applying concepts and skills from the chapter. 1. 2. 3. 4. 5. [end page] [begin page] [Formatter: this is the chapter opener photo, and should fill the page up to the Mini Investigation (below)] [CATCH C07-P01-OB11USB; Size CO; R; description to come in addendum photo ms] MINI INVESTIGATION: TITLE T/K Skills: text t/k Equipment and Materials: 1. 2. 3. A. B. C. D. E F. [end page] [BEGIN PAGE; 6 pages] 7.1 [catch C07-P02-OB11USB; Size D; Research. Photo of a snowshoe hare in the snow.] Figure 1 Snowshoe hares have evolved a number of adaptations that allow them to survive in winter: a coat that changes from brown to white and unusually wide feet for moving on deep soft snow. Biological Change Over Time Everywhere we look we see change. We live on a dynamic Earth, which we share with millions of other species, comprised of trillions of individual organisms. We observe life changing over time – individuals grow and mature and new generations come and go. The physical Earth also changes. Some changes are rapid, while others are slow and may go unnoticed. For example, you would observe a forest fire or the birth of an individual, but you might not observe the daily changes during ecological succession that follows a fire or the changes as an individual grows. The slower and more gradual the change, the more difficult it is to observe and investigate. As you learned in the Diversity unit, biologists are convinced that entire species change over time – they evolve. How do biologists detect such evolutionary changes in species and what causes them to occur? How might the environment influence evolutionary changes in species (Figure 1)? Change in Living Things Before discussing the evolutionary change of species in nature, it is useful to first examine the changes in species with which we are most familiar. Consider what you already know about genetic variation and change. How can this information be put to practical use in animal and plant domestication? All species, including humans, exhibit genetic variation. The original sources of genetic variation are mutations, which are changes in genetic information. Mutations create new genes which provide a continual supply of new genetic information. Mutations that enter populations have an immediate and direct effect on individuals, and also have the potential to influence future generations when they are inherited. Mutations neutral mutation mutations that do not result in any selective advantage or disadvantage harmful mutation any mutation that reduces the reproductive success of an individual and is therefore selected against; harmful mutations do not accumulate over time beneficial mutation any mutation that increases the reproductive success of an organism; beneficial mutations are favoured by natural selection and accumulate over time Mutations may be neutral, harmful, or beneficial. Most mutations are neutral and result in changes in DNA that have no immediate effect. Neutral mutations are those that provide no benefit or harm to the individual. Harmful mutations are those that reduce the reproductive success of an organism. Examples of harmful mutations include those that lead to serious genetic disorders such as cystic fibrosis or Huntington disease. Beneficial mutations are those that produce a change in an individual’s phenotype that gives the individual an advantage. Beneficial mutations give individuals a better chance of survival in their environment. For example, the sickle-cell allele for example, gives carriers a high degree of resistance to malaria and dramatically enhances their chances of survival in malaria endemic regions. The changes that arise in species through mutation can have significant consequences. Bacteria that exhibit resistance to antibiotics are becoming more widespread as less resistant strains are killed off (Figure 2(a)). Similarly, insect and other pest species that demonstrate resistance to various pesticides are becoming more common and difficult to control (Figure 2(b)). From the perspective of a bacteria or pest species, any mutations that confer increased resistance are beneficial. Humans, however, would consider these mutations undesirable. The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P03-OB11USB; Size B1; Research. Photo of highly resistant strain of bacteria (e.g. Staphylococcus aureus)] [catch C07-P04-OB11USB; Size B1; Research. Photo of a pesticide-resistant insect. Look for an Ontario example such as the Colorado potato beetle.] Figure 2 t/k pending image selection. [END PAGE] [BEGIN PAGE] [catch C07-P05-OB11USB; Size D; Research. Photo of someone getting a vaccination. Would prefer image showing an ethnic teen.] Figure 3 Each year millions of Ontarians receive the seasonal flu shot. A new vaccine is needed each year because the influenza virus is continuously changing. Some mutations have serious consequences to human health. For example, viruses, like living cells, carry genetic information that can undergo mutation. This means that populations of disease-causing viruses, such as the human influenza virus, are genetically variable, and change over time. In rare instances, a mutation may increase the virulence of a virus or enhance its ability to spread. The result can be a deadly epidemic. Each year the World Health Organization and other health agencies try to predict which particular virus strains poses the greatest threat to humans and they then work to develop an effective “flu” vaccine (Figure 3). The most obvious changes to species are those that have occurred with the domestication of numerous species of plants and animals. In most cases unmodified members of the original species still remain in the wild but in some cases such as that of certain breeds of domesticated cattle, the original species is now extinct. Changes that have occurred during domestication are a direct result of human manipulation. Selective Breeding: Artificial Selection of Traits artificial selection directed breeding in which individuals that exhibit a particular trait are chosen as parents of the next generation; artificial selection is used to produce new breeds or varieties of plants and animals The domestication of animals and plants is one of the most important technological innovations in human history. Domesticated plants and animals provide humans with the vast majority of our food supply and formed the basis for the development of modern civilizations. Domestication is the changing members of a species to suit human needs through controlled captive breeding. The controlled captive breeding process is referred to as artificial selection – artificial because it occurs in captivity rather than in a natural setting and selection because humans choose which specific animals or plants are bred. The breeder selects individuals that exhibit a desired trait or traits and uses them as the parents of the next generation. Humans have been domesticating animals and plants for more than 10 000 years. You might be surprised to learn that the earliest animal to be domesticated was Canis lupus, the wolf (Figure 4). Of course we no longer refer to the domesticated variety as wolves but rather as dogs. Genetic evidence provides compelling evidence that all modern breeds of dogs are descended from wolves (Figure 5). For this reason, dogs are considered a subspecies of wolves and given the scientific name Canis lupus familiaris. [catch C07-P07-OB11USB; Size B; Research. Image of many different dog breeds.] [Formatter: place fig4 & fig5 side by side across page; in the correct order] [catch C07-P06-OB11USB; Size D; Research. Photo of a wolf, must be Canis lupis. Would prefer to see a nice head shot or a clear profile.] Figure 4 The wolf, Canis lupus, is the ancestral species to all modern dog breeds. Figure 5 Thousands of years of artificial selection have produced a great variety of dog breeds. During this time a single mutation is thought to have produced a dog with achondroplasia – a form of dwarfism. The descendents of this dog have since given rise to bassets and dachshunds. [END PAGE] [BEGIN PAGE] Plants are equally capable of being selectively bred to suit our needs. For example, several thousand years of domestication of the wild sea cabbage, Brassica oleracea, has produced a wide array of vegetables (Figure 6). These diverse vegetables are, in fact, altered forms of the same original species. They look and taste different as a result of artificial selection acting over thousands of generations. [catch C07-F01-OB11USB; Size B; New. Art showing the seven well-known domesticated vegetables that are included in the sea cabbage family tree.] Figure 6 These seven well-known vegetables are domesticated varieties of the wild sea cabbage. Table 1 Domesticated species and the areas they originated in. Region Domesticated species Eurasia [t/k] North and South America [t/k] Africa [t/k] How does artificial selection work? How can animal and plant breeders turn wolves into Chihuahuas and St. Bernards, and wild cabbage into broccoli and kohlrabi? The process is surprisingly simple but, with the exception of modern genetic engineering techniques, very slow. The breeder usually has a particular feature in mind. For example, native peoples of Mesoamerica domesticated the tomato. Wild tomato plants produce nutritious but small fruit (Figure 7). As with any species, these plants exhibited variability – some were a little larger than others, some produced larger fruits, and some tasted better than others. Generation after generation, farmers selected seeds from the best plants to sow the next season. The seeds germinated, grew, flowered, and then cross pollinated each other producing more fruit with the desired traits. Again the farmers consumed most of the fruit as food, but carefully examined the plants and saved seeds from the very best plants for sowing. These practices happened in many parts of the world (Table 1). The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P08-OB11USB; Size B1; Research. Photo of wild tomatoes.] [catch C07-P09-OB11USB; Size B1; Research. Photo of domesticated tomatoes] Figure 7 Beginning with (a) a wild species of tomato farmers chose only those plants that exhibited the most desirable characteristics as a source of seeds for the next generation of planting. The result of thousands of generations is (b) the modern tomato. [END PAGE] [BEGIN PAGE] THE SCIENCE OF BREEDING Most traditional animal and plant breeders would not consider themselves scientists but what they do is often equivalent to a tightly controlled experiment. Each time breeders attempt to develop a new breed, they are testing a hypothesis and following a common set of procedures: Hypothesis: By selecting for breeding stock individuals with certain favoured CAREER LINK Animal or Plant Breeder Animal or plant breeders ...[t/k] ...... To learn more about becoming an animal or plant breeder, Go to Nelson Science. traits over others, the favoured trait will become more prevalent and more pronounced. Independent Variable: Breeding population (selected by the breeder) Dependent Variable: Appearance of favoured trait in population Procedure: 1. Choose a useful species that can be bred in captivity. 2. Breed a large number of individuals. 3. Choose a trait that you wish to favour, such as large size, a particular colour, or sweetness. 4. Identify individuals that exhibit the favoured trait most strongly. 5. Breed only these individuals to produce the next generation of individuals. 6. Repeat Steps 4 and 5 over many generations. In most cases the hypothesis is confirmed. The favoured trait becomes widespread throughout the population and also becomes enhanced. What early breeders likely did not expect was the degree to which the populations would change. [catch career link icon] Modern breeding, particularly of crop plants, has undergone a revolution. Today scientists are routinely using genetic engineering techniques to transfer what they hope will be beneficial genes from an individual of one species to an individual of another species. When successful, the genetically modified individual is often mass-produced by cloning. This practice can result in the widespread use of genetically modified plants with little or no genetic diversity. Although the pros and cons of genetic engineering are hotly debated, one thing is certain: these genes have all arisen in natural populations and a loss in biodiversity also results in a loss of potentially valuable genes. THE POWER OF ARTICIFICAL SELECTION The most unexpected result of artificial selection is the production of individuals that exhibit characteristics that are far beyond the natural variability witnessed in the original breeding population. Adult Chihuahuas are not simply small wolves, they are much smaller than even the smallest of adult wild wolves and they look very different. Giant red tomatoes can be a hundred times larger than the largest wild tomato fruit. Looking back to the traits of the first wild plants and animals used for breeding, no one could have imagined the power of selective breeding (Figure 8). The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P10-OB11USB; Size B1; Research. Photo of a giant pumpkin with a person in the photo for perspective] [catch C07-P11-OB11USB; Size B1; Research. Photo of a Texas longhorn] Figure 8 Artificial selection can produce surprising results, such as this giant pumpkins or the long horns of this Texas Longhorn. [END PAGE] [BEGN PAGE] Artificial selection methods can also lead to the reduction in genetic diversity within a population. If breeders only favour certain traits within a population, then the many alleles linked to other versions of a particular characteristic are reduced or eliminated. Such a loss in diversity makes a population more vulnerable to disease. For example, large cobs of sweet corn might be favoured by plant breeders but might also be favoured by insect pests. In addition, some favoured traits can be linked to alleles that are detrimental. For example, some breeds of dogs are more prone to genetic disorders such as hip dysplasia or cancer because the alleles associated with these disorders are inherited along with the same alleles that produce the favoured traits of those particular breeds. [FORMAT AS 2 COLUMNS WITH FULL PAGE MEASURE AND INCLUDE WHEAT FIGURE IN BOX.] RESEARCH THIS: THE RICH HISTORY OF DOMESTICATION Skills: [tk] [catch Skills Handbook icon: t/k] Many species have been the subject of artificial selection. They include livestock, pets, food crops, and ornamental plants (Figure 9). Each has a fascinating history that began in some part of the world where the original wild species lived. In this activity, you are to choose a domesticated species and investigate its past. [catch C07-P12-OB11USB; Size D; Research. Photo of wheat clearly showing an individual head of wheat.] Figure 9 Wheat originated in Turkey. It was selected for large seed size and non-shattering heads, so that farmers could collect the seeds before they dispersed. 1. Choose a domesticated plant or animal. 2. Research the history of the plant or animal’s domestication. 3. Research the various breeds or varieties that currently exist. Are the breeds rare? popular? newly established? 4. Consider the benefits and/or harm caused by the domesticated species. A. How is the domesticated species of value to humans today? B. How long has the species been under domestication and in what part of the world did it originate? C. How much has the species been altered as a result of artificial selection? D. Is there evidence that artificial selection has caused a serious loss in genetic diversity within the population? E. How many different breeds or varieties exist today and how do they differ from each other? F. Comment on the overall influence of the domesticated species on humans and on the environment. Do you think that species domestication was a good idea? [END Research This] THE HUNDRED YEAR EXPERIMENT The longest running formal experiment in artificial selection is being conducted by the Illinois State Agricultural Research Station. The experiment began in 1896 and it still underway. The purpose of the experiment was to test the effect of artificial selection on oil content of corn seeds. The design involved two separate breeding experiments. In the first, corn plants were selected for high oil content, whereas in the second experiment they were selected for low oil content. Over 76 years, the oil content increased from 5% to more than 18% in the first experiment while it dropped to less than 1% in the second (Figure 10). [catch C07-F02-OB11USB; Size D; New/Permissions. Graph of experimental results for the hundred year experiment. ] Figure 10 Artificial selection can increase or decrease the oil content in corn. LIMITATIONS OF ARTIFICIAL SELECTION: THE INFLUENCE OF MUTATIONS Not all attempts at artificial selection have been successful. Breeders cannot create traits that do not already exist in some form within the population. If there are no genes for blue roses (long sought after by flower lovers), then no amount of cross breeding will create one. Breeders must work with the genetic diversity that already exists in the population. This does not mean that new mutations cannot arise however and when this happens the breeder has new material with which to work. There is always room for hope that someday a mutation will occur that gives rise to a truly blue rose. Beneficial or neutral mutations have a good chance of being passed on to future generations because they are either favoured or go unnoticed. In contrast, mutations that cause harm, or produce an undesirable trait in an individual, have little influence on the potential success of artificial selection efforts. Breeders simply do not choose such individuals for breeding and therefore the harmful mutations are not passed on to the next generation. In rare circumstances an undesirable trait may accompany a beneficial one. An interesting example occurred in the breeding of strawberries. Breeders were able to develop plants with high quality berries held on elevated stocks making them much easier to harvest. Unfortunately the berries were purple in colour! Attempts at commercialization failed. A number of farmers produced these berries but consumers simply rejected them based on their odd colour. [END PAGE] [BEGIN PAGE] Implications for Natural Populations How can we apply our current understanding about genetics and artificial selection to the millions of species that exist in the wild? We should first recap what we already know about genetics: • Individuals of all species exhibit genetic variation. • Mutations produce heritable changes in individuals and these changes may be beneficial, harmful, or neutral. • Some species, such as bacteria and insects, can change over relatively short periods of time. • Some domesticated species have changed dramatically under the influence of artificial selection. These observations are based on a large number of species that have been domesticated over relatively short periods of time – at most over several thousand years. How, then, might similar processes influence the populations of all species on Earth? If we can begin with a population of wolves, and change them into hundreds of distinct breeds of dog, what might happen to a species over thousands or millions of years living under natural conditions? One of the challenges faced by biologists trying to answer these questions is how and where to obtain useful evidence. You can imagine that one of the most useful places for biologists to look would be back in time. Biologists do not have time machines but fortunately Earth keeps some records of the past history of life. A history that is recorded in the rocks and in at least some locations, actually opened to views of the past (Figure 11). 7.1 SUMMARY [catch C07-P13-OB11USB; Size D; Research. Photo of the grand canyon, illustrating that it was formed by erosion.] • Mutations create new genetic information and add genetic diversity to species • Beneficial mutations can have significant consequences for species. • Artificial selection works by choosing individuals with particular favoured traits in each generation as the breeding stock for next generation. • When practiced over many generations, artificial selection can produce dramatic changes in the traits of a population. • Artificial selection is limited by the genetic variability within the breeding population. • Artificial selection methods can reduce the overall genetic diversity of the population and therefore contribute to the loss of biodiversity. 7.1 QUESTIONS [FORMATTER: RUN IN TWO COLUMNS ACROSS PAGE] Figure 11 The grand canyon was formed by erosion. The Colorado river has cut through and exposed sedimentary deposits that are hundreds of millions of years old. 1. The chances of any one individual being born with a beneficial mutation is very low. How then is it possible for mutations to play such a key role in evolution? [K/U] 2. How might it be possible for a neutral mutation to play an important role in the evolution of a species? [K/U] 3. Explain why harmful mutations do not accumulate over time and cause harm to populations. [K/U] 4. Use the sickle-cell allele to show how a mutation may be beneficial or harmful depending on the environment. [K/U] 4. Use the evolution of antibiotic resistant to show how a mutation that is advantageous for one species can be harmful for another. [K/U] 5. Most wolves look quite similar. Use the domestication of dogs to illustrate the genetic diversity that is contained within the wolf population. [K/U] 6. How have modern genetic engineering methods changed the way that plant breeders develop plants with new and potentially valuable traits? [K/U] 7. Using a specific example, outline a hypothesis and simple step by step procedure a breeder could use to create a breed with a desired trait. [K/U, T/I] 8. How does the genetic diversity of a population and mutation rates limit the ability of breeders to create organisms with desired traits? [K/U, A] 9. What characteristics of bacteria and insects enable them to evolve relatively quickly? [K/U] 10. All domestications of plants and animals begin with humans selecting a wild species living nearby. Do research to find out where each of the follow domesticated species originated: [T/I, A] (a) chicken (b) pig (c) cattle (d) corn (e) wheat (f) rice (g) chocolate 11. [research question about genetic mutations to cover C2.2] 12. [add question referencing single mutation leading to short legs in dog breeds.] [END PAGE] [BEGIN PAGE; 6 pages] 7.2 immutable something that cannot be changed The Evolution of an Idea Dating back at least as far as Aristotle (384-322 BCE) most Europeans accepted the idea that the Earth and all living things had been created in their present forms and were immutable – they could not change and had not changed. The explanations for all natural phenomena proposed by Aristotle and others were largely based on strongly held religious beliefs, philosophical debate thoughtful conjecture. It was not until science began to come of age in the 15th to 18th centuries, that European philosophers recognized the importance of careful observation, experimentation, and deductive reasoning. It was during this time that Copernicus, Galileo, and Newton demonstrated the power of science to explain the laws of motion both on Earth and in the heavens above. The Seeds of an Idea [catch C07-P14-OB11USB; Size D; Research. Image of the (vestigial toes of a pig)— illustating that they do not touch the ground.] Figure 1 Many mammals, including pigs, have toes that do not reach the ground. Buffon puzzled over such useless features and considered them strong evidence that these species had changed over time. A French scientist Comte (Count) Georges-Louis Leclerc de Buffon (17071788) applied scientific methods to the detailed study of anatomy. He closely examined animal body structures, considered their functions, and tried to account for his findings. Buffon was puzzled by anatomical features that seemed to serve no purpose. For example, he wondered why pigs have extra toes that do not reach the ground (Figure 1). Buffon believed the species had been created in a more perfect form, but that they had changed over time. At about the same time, other prominent scientists, including Carl Linnaeus (1707-1778) and Erasmus Darwin (1731-1802), also proposed that life changed over time. Erasmus Darwin, the grandfather of Charles Darwin, even suggested that all life might have evolved from a single original source. While the seeds of evolutionary thought had been sown, these scientists could offer no explanation for how living things change. Without a plausible mechanism to explain how a species could change, their ideas remained speculative. Adaptation and Heredity [catch C07-P15-OB11USB; Size D; Research. Photo of an athlete in training with obvious strong muscles.] Figure 2 Muscles increase in size in response to vigorous exercise. Such an increase in size is considered an acquired characteristic A student of Buffon, Jean-Baptiste Pierre Antioine de Monet, Chevalier de Lamarck (1744–1829), was the first scientist to offer a possible mechanism for the evolution of species. Lamarck proposed that evolutionary change resulted from two distinct principles. Lamarck’s first principle was that of use and disuse. He believed that structures an individual used became larger and stronger, while structures that were not used became smaller and weaker. On the surface, this principle seems to be supported by evidence from everyday observations. When athletes train, their muscles respond by getting stronger and increasing in size (Figure 2). Conversely, astronauts that return from space have reduced muscle mass resulting from lack of use. It seems reasonable to think that similar responses to use and disuse might occur among all organisms. Lamarck’s second principle was the inheritance of acquired characteristics. Lamarck believed that individuals could pass on to their offspring characteristics they had acquired during their lifetime. He believed, for example, that if adult giraffes stretched their neck during their lifetimes, then their offspring would be born with slightly longer necks. [END PAGE] [BEGIN PAGE] To Lamarck, these two principles could explained why species were so adapted to their environment and how they could evolve if the environment changed. If the climate gradually cooled, animals might respond by growing a thicker coat of hair and would pass on this acquired characteristic to their offspring. Their offspring would then be born better adapted to the changing environment. The example of the giraffe’s neck is often used to illustrate Lamarck’s theory (Figure 3). [catch C07-F03-OB11USB; Size B; New. A series diagram showing Lamarck’s theory of evolution by the inheritance of acquired characteristics.] Figure 3 Lamarck’s theory of evolution by the inheritance of acquired characteristics. Today we know that Lamarck’s theory was is flawed. Although organisms can acquire many characteristics during their lifetime, many features do not change in response to use and those features that do change are not normally heritable. For example, your vision does not improve the more you use your eyes. It is possible to stretch your neck slightly, but this will not alter your DNA and your children will not be born with longer necks. Despite Lamarck’s flawed theory, he did make a number of very significant contributions to our understanding of evolution. Lamarck proposed the following: • All species evolve over time. • Species evolve in response to their environment and become better adapted to that environment. • Changes are passed on from generation to generation. Lamarck’s theory stimulated a great deal of scientific discussion and his contributions provided a sound basis for the theory of evolution that would follow. Patterns of Change Even scientists that did not accept the idea that species could change were finding evidence that was extremely puzzling. They found some of this evidence in the form of fossils, which are preserved ancient remains of dead organisms. A minimum age of 10 000 years is sometimes used as a criteria for being designated as a fossil. [END PAGE] [BEGIN PAGE] fossil any ancient remains, impressions, or traces of an organism or traces of its activity that have been preserved in rocks or other mineral deposits in the Earth’s crust. Hardened body parts such as bone and shell are the most common fossilized remains Fossil Formation Most fossils are in the form of hard impressions in solid rock Many leave little doubt as to what they represent. No one could mistake a well-preserved fossil of Knightia (Figure 4(a)) for anything other than a fish, or fail to recognize an obvious fossilized leaf (Figure 4(b)). It seemed self evident to most scientists that such fossils had been formed by once living organisms. The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P16-OB11USB; Size B1; Image of Knightia.] [catch C07-P17-OB11USB; Size B1; Research. Image of a leaf fossil.] Figure 4 Fossils of both (a) Knightia and (b) leaves are extremely abundant in some from rock formations. The most common and easily recognized fossils are of hard body parts such as bones, teeth, and shells. Fossils are formed when the remains of a buried organism are gradually replaced by mineral deposits (Figure 5). After an organism dies, the body usually decomposes. However, if the body sinks to the bottom of a body of water and is quickly buried by sediments, the resulting lack of oxygen can prevent decomposition. As sediments accumulate over time, the body becomes compressed, and very gradually chemical changes occur that result in the body being mineralized. [Formatter: This 4-part image will go across text width in two rows of two (i.e. 2 * 2). It can go full page width if that works better, but with minimal height—see notes in art ms.] [catch C07-F04a-OB11USB; Size B1; New. Image showing how a fossil forms underwater. Part a: a dead organism underwater] [catch C07-F04b-OB11USB; Size B1; New. Image showing how a fossil forms underwater. Part b: an organism becomes buried in thick sediments] [catch C07-F04c-OB11USB; Size B1; New. Image showing how a fossil forms underwater. Part c: the sediments and chemical action change the organism in to a mineral form over time] [catch C07-F04d-OB11USB; Size B1; New. Image showing how a fossil forms underwater. Part d: the fossil is uncovered through erosion and excavation.] Figure 5 Most fossils form underwater a) when an organism becomes buried in thick sediments b).The organisms does not decay because of a lack of oxygen. Over time the pressure of the sediments and chemical action change the organism into a mineralized form. c). Fossils dating back millions and even billions of year may be found when such deposits are excavating [END PAGE] [START PAGE] Organisms can also become trapped and preserved in amber – fossilized tree sap (Figure 6). Some of the most well preserved fossils are formed when entire organisms become trapped in materials that conserve the chemical remains of the organism. Such can be the case when organisms are trapped in volcanic ash, ice formations such as permafrost, or acidic bogs. The necessary conditions for fossil formation are rare. When oxygen is present, bodies usually decompose too quickly to fossilize. Therefore, only organisms that die in low-oxygen locations will fossilize. Most often these are aquatic organisms living in locations where sediment is continuously deposited on the bottom. In addition, organisms with hard body parts are much more likely to be preserved than soft bodied organisms. As a consequence, fossils of marine organisms with hard body parts such as clams and snails are very common, whereas fossils of land animals and plants are much less common. Dinosaur fossils are extremely well known but are very rare by comparison to fossils of marine organisms. Fossils can also be formed from footprints, burrows, and even faecal remains. Sediments may fill in a footprint or burrow and then harden over time to create a fossil (Figure 7). [formatter: place figures 6 & 7 next to each other in the text measure] [Catch C07-P52-OB11USB; Size B1; Research. Photo of an insect in amber.] [catch C07-P18-OB11USB; Size B1; Research. Photo of a fossilized footprint, preferably of a dinosaur such as sample image.] Figure 6 [t/k] Figure 7 Under the right conditions, footprints can become fossilized. Reading The Fossil Record [C07-P19- OB11USB; Size D; Research. Photo of a triceratops skeleton at a museum.] Figure 8 Fossils of dinosaurs like this triceratops leave little doubt that some fossil species are dramatically different than any species alive today. At first scientists may have speculated that fossils were nothing more than recently living organisms that had become trapped in muddy deposits and then hardened over a relatively brief period of time. Perhaps fossils were just preserved plants and animals that were no more than a few hundred or a few thousand years old. This simple explanation was quickly contradicted by a number of observations that are very difficult to account for: • Many fossils appear to be of unusual and unknown organisms. There are fossils of thousands of species that are no longer living (Figure 8). • There are no fossils of most living species. • Fossils are often buried very deep within rock formations. Some are more than a kilometre below the Earth’s surface. • Fossils are often found in unexpected locations. For example, fossils of sea life are found high in mountain formations and in present-day deserts. Such observations were of great interest to early scientists. They became determined to develop a better understanding of how fossils formed and to understand what they could tell us about life in the past. This emerging science that studied fossil organisms to learn about prehistoric life was called palaeontology. [END PAGE] [START PAGE]Palaeontologists used fossils to provide evidence that life had been very different in the past. Also, around this time, the field of geology, the study of Earth’s surface features, was beginning to develop. Two prominent scientists, a paleontologist named George Cuvier and a geologist named Charles Lyell, began to provide a wealth of new evidence on how species and Earth might change over time (Figure 9). <career link paleontologist> Catastrophism and Uniformitarianism palaeontology the scientific investigation of prehistoric life through the study of fossils The famous palaeontologist Georges Cuvier (1769-1832) conducted the first detailed studies of fossils. Cuvier noted the following: • Fossils of very simple organisms are found in all depths of fossil deposits. • Fossils of more complex organisms are only found at shallower depths, in [catch C07-P20-OB11USB; Size D; Research. Photo of a paleontologist working with a large fossil—either in a museum or in the field.] Figure 9 A paleontologist works on a Tyrannosaurus rex fossils at the Tyrell Museum in Drumheller, Alberta. younger rock. • Fossils in the shallower depths are more likely to resemble living species. • Rock layers contain fossils of many species that do not occur in layers above or below them (Figure 10). [catch C07-F05-OB11USB; Size B; New. Image of fossils in strata showing gradually increasing complexity from bottom to top. ] [Formatter: Place next to subhead, Catastropism...] CAREER LINK Paleontologist Paleontologists are scientists that study ancient fossilized remains. Their work may require expeditions to different parts of the world. To learn more about becoming a paleontologist, [catch web link banner] catastrophism the theory that the pattern of fossils could be accounted for by a series of global catastrophes that wiped out most species on Earth uniformitarianism the theory that geological changes are slow and gradual and that natural laws and processes have not changed over time Figure 10 Cuvier noticed that all fossils from deeper layers were simpler than the most complex fossils above. Such observations offered strong support for the theory that life had evolved from simple to more complex forms over time. The oldest fossil deposits contain only simple life forms. More recent fossil deposits contain species that are both more complex and more similar to present living species. Although the fossils Cuvier found showed a clear pattern of change from layer to layer, Cuvier believed that species themselves did not change. Instead, he proposed a theory of catastrophism. According to the theory of catastrophism, global catastrophes, such as floods, had caused the widespread extinctions of species. These extinct species, some of which were fossilized, were then replaced by a newly created set of species. Cuvier’s theory accounted for the different groups of species in each layer but did not adequately account for why each layer included progressively more complex forms. At about the same time that Cuvier was postulating catastrophism, Charles Lyell (1797-1875) was studying rocks and fossils and coming to the opposite conclusion. Considered the father of modern geology, Lyell revolutionized geology with his theory of uniformitarianism. In 1830, Lyell put forth the following principles of uniformitarianism in his now famous Principles of Geology: • Earth has been changed by the same processes in the past that are occurring in the present. • Geological change is slow and gradual rather than fast and catastrophic. • Natural laws that influence these changes are constant and eternal and they operated in the past with the same intensity as they do today. [END PAGE] [BEGIN PAGE] Lyell’s ideas were radical. He was proposing that entire mountain ranges might have formed by extremely slow processes, and that deep gorges were the product of slow erosion. Lyell’s theories directly challenged the belief in a very young Earth. If he was right, Earth was extremely old and life had had a very long time to undergo evolutionary change (Figure 11). [FORMAT HOWEVER WORKS BEST FOR THE PAGE] RESEARCH THIS: PALAEONTOLOGY AND GEOLOGY Skills: Researching, Communicating, Evaluating The anatomist and palaeontologist Baron George Cuvier and the geologist Sir Charles Lyell made substantial contributions to our early understanding of history of life on Earth. In this research activity, you will partner with a fellow student and investigate the contributions of these individuals. 1. With your partner, research the lives of Cuvier and Lyell. When and where they were born? What was their social status, upbringing, and education? Take note of any unusual aspects of their lives. 2. Document Cuvier’s and Lyell’s contributions to palaeontology and/or geography. Include their association with the [catch C07-P21-OB11USB; Size D; Research. Photo of the Grand Canyon that accentuates depth of the canyon and shows layers of rock.] Figure 11 [t/k] following theories: catastrophism, actualism, and uniformitarianism. A. Create a short “biographical sketch” of these two individuals. B. Summarize their contributions to science. In what ways did they break new ground in our scientific understanding of Earth and life on Earth? The Stage is Set By the 19th century, scientific thoughts regarding the history of Earth and its life forms were undergoing substantial change. There was growing evidence that Earth was ancient and that species might be evolving. However, a mechanism for such change had yet to be adequately explained. Furthermore, Lamarck’s contributions to thoughts on evolution were significant but his explanation for how life evolves was unsatisfactory. However, unlike the debate over the age of Earth, tThe search for a mechanism for evolution would not have to wait for very long. It was to become the life’s work of a young man named Charles Darwin. 7.2 SUMMARY • By the 18th century scientists were beginning to gather evidence that supported the theory that life had changed over time. • Lamarck was the first scientist to recognize that species evolved in response to their environment, but his hypothesis of how species evolved has proven to be incorrect. • Fossils provide compelling evidence that species living in the past were different than those living in the present. • Fossils show a progression of an increasing complexity of organisms over time with the most complex organisms being found only more recent fossil deposits. • Lyell proposed that those of the Earth’s geologic features can be accounted for by very slow changes occurring over very long periods of time. • Cuvier proposed that species did not change but were eliminated by catastrophic events only to be replaced by newly created forms. 7.2 QUESTIONS 1. (a) Why was Buffon puzzled by pig’s toes? [K/U] (b) How did he explain them? 2. What explanation did Lamarck propose for how species had changed over time? [K/U] 3. What role did Lamarck believe the environment played in evolution? [K/U] 4. Use Lamarck’s theory to explain the evolution of running speed in Cheetahs. [K/U, A] 5. What do the following characteristics of fossils reveal about the history of life on Earth. [K/U, A] (a) Some fossils of marine organisms are discovered at high elevations in mountains. (b) Most fossils are of species that are no longer living. (c) most living organisms are not found in the fossil record. (d) Most fossils are of marine organisms. (e) The oldest fossil deposits only contain simple organisms. More recent deposits contain both simple and complex fossils. 6. How did the theory of catastrophism account for patterns seen in the fossil record? [K/U] 7. How did the theory of uniformitarianism account for patterns seen geology? [K/U] 8. Use labelled sketches to illustrate the process of fossil formation. [K/U, C] 9. How might it be possible for fossils to provide evidence about the behaviour of an organism? [A] 10. Imagine you were asked to excavate fossils from deposits near the top of the grand canyon and near the bottom. Predict any pattern you would expect to find in the fossils. [T/I, A] 11. The most famous fossil deposit in Canada is the Burgess Shale. Do research to answer the following questions. [T/I, A] (a) Where are the Burgess Shale located? (b) When and by whom were they discovered? (c) What is the age of the fossils in the deposit? (d) What makes the deposit of special interest? [END PAGE] [FORMATTER: Please format Journal as per Design (it is a Science Journal); 2pp total] 7.3 The Voyage of the Beagle ABSTRACT [FORMATTER: RUN FULL PAGE WIDTH, AS PER DESIGN] Charles Darwin’s five-year voyage aboard the HMS Beagle stimulated his curiosity and set him on the path to great discovery. Darwin’s keen powers of observation, exhaustive collections, and new findings provided a wealth of evidence on the origin of species. Darwin was puzzled by many of his observations that could not be explained based on his previously held beliefs. Darwin would devote much of his life to developing a theory that could account for his many observations. [Formatter: run the rest of the text in 2 columns, as per design] Introduction In December 1831, Charles Darwin set sail on the HMS Beagle and began a five-year voyage of discovery (Figure 1). The young Darwin, age 22, had been recommended for the voyage by his former Professor John Henslow, who considered Darwin an exceptional naturalist. [C07-P23-OB11USB; Size C3; Research. Photo of fossil Glyptodon without much background detail.] [catch C07-P24-OB11USB; Size C3; Research. Photo of a present day armadillo.] [catch C07-P22-OB11USB; Size C2; Research. Photo of the young Charles Darwin.] Figure 2 The (a) fossil Glyptodon resembled the (b) present day armadillo except that the Glyptodon was almost 200 kg heavier. Figure 1 [t/k] Darwin also discovered fossils of marine organisms high in the Andes Mountains. Later, following a severe earthquake, he was informed that a section of coastline had risen three metres out of the water as a result. This evidence supported Lyell’s theory that such events could, over millions of years, account for large-scale changes like the formation of mountain ranges. By the time Darwin left South America, he was becoming increasingly convinced that the Earth was indeed dynamic and changing. Captain Robert Fitzroy’s, primary mission was to survey and map the coastal waters of South America for the British Navy. Darwin was to observe, record, and collect specimens of rocks, minerals, plants, and animals. His supplies included specimen jars and preservative, a microscope, binoculars, a compass, many notebooks, a pistol, a rifle, and a book given to him by Henslow – the first volume of Lyell’s Principles of Geology. What Darwin Saw As the crew of the Beagle was conducting surveys along the east and west coast of South America, Darwin hired guides and porters and travelled inland to explore, often for weeks at a time. Darwin was impressed by the diversity of life he encountered, the grandeur of the rich tropical rainforests, and the geographic features of the landscape. He was keen to document everything he saw. Darwin was a meticulous observer and painstaking collector. During the voyage he gathered thousands of specimens and filled notebooks with more than 4000 pages of detailed observations. At intervals Darwin would ship his specimens back to England to be looked at by experts. His many rock, mineral, and fossil specimens were particularly heavy and in a 1932 letter to Henslow, who had agreed to receive his specimens, Darwin wrote: “I am afraid you will groan, or rather the floor of the Lecture room will, when the casks arrive.” While in Patagonia, Darwin made some important discoveries including fossils of giant Glyptodon (Figure 2) and Megatherium. Darwin would later find out that these specimens resembled the much smaller modern armadillos and sloths, respectively. Darwin noted that modern and extinct animals that resemble each other seemed to share similar geographical distributions. In this case, like their fossil relatives, modern-day armadillos and sloths are both found in South America. The Galapagos Islands The most famous of Darwin’s observations and conclusions were on the Galapagos Islands, lying approximately 1000 km off the west coast of South America (Figure 3). This small isolated archipelago is comprised of 18 islands, which were formed from volcanoes that rose up from the ocean floor. Upon his arrival Darwin was immediately struck by the harsh dry landscape and the unusual and unique flora and fauna that inhabited the islands. Among the most unusual species were tame birds, such as the nesting boobies, that you could walk up to, an iguana that dives underwater to feed on seaweed, and the giant land tortoises (Figure 4). [formatter: The next two photos will run side-by-side across column width. Should have the same orientation.] [catch C07-P26-OB11USB; Size C3; Permission. Photo of a Galapagos marine iguana.] [catch C07-P27-OB11USB; Size C3; Permission. Photo of a species of Galapagos tortoise.] Figure 4 The (a) Galapagos marine iguana and (b) a species of Galapagos tortoise Formatter: Place map at top of second page and make it full page (2 column) width. [catch C07-F06-OB11USB; Size A; New. Map showing Darwin’s voyage.] [formatter: The next two photos will run side-by-side across column width.Should have the same orientation.] Investigation X.X.X 21 resembled species in mainland South America; they did not live there. Darwin’s Return [Formatter: place C07-P25 as an inset photo on top of C07-F06.] [catch C07-P25-OB11USB; Size E; Research. Photo of the HMS beagle.] igure 3 Darwin spent 5 years on the HMS Beagle. The HMS Beagle was 27.5 m in length and carried 74 people. Darwin’s cabin was so small that to lie down he had to remove a draw from the end of his bunk to make room for his feet. Oddly, these species bore a striking resemblance to species he had observed on the continent of South America even though they lived in entirely different habitats. Moreover they were very unlike the species he had observed on the Cape Verde islands off the coast of Africa although the habitat was similar to the Galapagos. As he went about collecting specimens, it did not occur to Darwin that neighbouring islands, often within sight of each other, might be home to entirely different species. Only later would he learn from experts that many of the specimens he had assumed were just varieties of a single species, were different species entirely, including the 13 species of Darwin’s finches that are now famous. Perhaps as surprising were the species that were absent from the Galapagos. There was not a single native species of amphibian or large land mammal in the entire Galapagos, even though some of these islands were over a 100 km in length. Darwin realized that the only types of species that did live in the Galapagos were those that could have arrived by air or water. Insects, birds, plants (seeds), and reptiles, which can go weeks without eating or drinking, could have arrived by air or water. Amphibians perish in salt water and no large mammal can survive without fresh water for long. It seemed the islands had been populated by species that had arrived from elsewhere. However, most of these species only Darwin had left England believing that species were immutable, but returned five years later with many doubts. Darwin was an individual of extraordinary determination. He would spend the next 20 years of his life formulating his theory of evolution and unravelling what he referred to as “that mystery of mysteries." The influence of the Beagle voyage is captured in Darwin’s own journal entry of 1837 “... Had been greatly struck ... on character of S. American fossils—& species on Galapagos Archipelago. — These facts origin (especially latter) of all my views.” Further Reading Darwin, Charles. (1839). The Voyage of the Beagle. Available online. Darwin, Charles. (1835). Galapagos Notebook. Available online as part of The Complete Work of Charles Darwin. Stewart, P.D. (2007). Galapagos: The Islands that Changed the World. New Haven: Yale University Press. 7.3 QUESTIONS 1. What qualities of a good scientist did Darwin display on the voyage? [K/U] 2. Describe Darwin’s key observations regarding the distribution of fossils. [K/U] 3. Darwin was surprised by the species he found on the Galapagos Islands. [K/U, T/I, A] (a) Of what other species did they remind him? (b) Why had Darwin expected to find species similar to those on the Cape Verde islands? (c) What is the connection between the types of native animals on the Galapagos and their ability to cross the open ocean? 4. Form a small group of two or three students, and conduct online research to complete the following: [T/I, A] (a) Examine Darwin’s childhood and formal education. (b) Find out the circumstances that lead to Darwin’s selection and his acceptance for participation in the voyage. (c) Describe the life history of at least one species of Galapagos wildlife. (d) Outline some of Darwin’s other scientific findings on the voyage, including his investigation of coral reefs. (e) Describe Darwin’s work ethic and approach to science. Did Darwin conduct any experiments of his own? Did he rely on the opinions of others? (f) Explore the relationship between Darwin and Captain Fitzroy. 5. Select and present in the form of a skit one piece of biographical information you gathered in Question 4. [C] Investigation X.X.X 22 [begin page; 8pp] 7.4 The Preponderance of Evidence Charles Darwin returned to England in 1836, ending his voyage on the HMS Beagle. Darwin had spent five years making countless observation and gathering thousands of specimens. He was now filled with new ideas and questions about species. In July of 1837 Darwin began writing his first notebook on what he called the “transmutation of species.” It would mark the beginning of Darwin’s farreaching investigations on the evolution of species. In a letter to his friend J.D. Hooker in 1844, Darwin described his approach: “I was so struck ... that I determined to collect blindly every sort of fact, which could bear any way on what are species. I have read heaps of agricultural and horticultural books, and have never ceased collecting facts.” In the years that followed, Darwin stayed true to his words, continuing to consult experts, conduct numerous experiments, and spend long hours contemplating his findings. This section will present the many forms of evidence that convinced Darwin of the evolution of species and enabled him to formulate his theory. Biogeography biogeography the scientific study of the geographic distribution of organisms based on both living species and fossils Some of the most compelling evidence for evolution comes from biogeography, the observed geographic patterns of distribution of species. Darwin’s observations of both living and fossilized species during the voyage of the Beagle laid the foundation for this new science. Darwin was particularly surprised by the unusual assortment of species he found on the Galapagos Islands. Though not witnessed by Darwin, other remote islands, including New Zealand and Hawaii, held similarly odd collections of species (Figure 1). The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P28-OB11USB; Size B1; Research. Photo of the New Zealand Kakapo in natural habitat.] [catch C07-P29-OB11USB; Size B1; Research. Photo of a Sifaka lemur in its natural habitat] Figure 1 (a) The New Zealand Kakapo is a giant nocturnal parrot and the world’s largest and only flightless parrot. It is critically endangered. (b) Sifaka lemurs are found only on the island of Madagascar but there are fossils in India. [catch C07-P30-OB11USB; Size D; Research. Photo of humans interacting with tame species on Galapagos or other.] Remote islands are also associated with unusual examples of animal behaviour. Many species are unusually tame (Figure 2). Such behaviour surprised Darwin and is immediately apparent to any present-day tourist visiting these remote environments. Birds may land on your head, iguanas will allow themselves to be picked up, and sea lions are content to have you sit next to them on the beach. Darwin believed that this lack of fear of people could also be accounted for by evolution. Perhaps these species, living and evolving in a location with no natural predators had lost their instinctive fear. Darwin’s Hypotheses Figure 2 Many species that live on remote islands show little or no fear of humans. Darwin realized that the patterns he had observed regarding the distribution of species, both living and extinct, was evidence that species might have evolved. He hypothesized that remote oceanic islands became populated by species that arrived by water or air, and then many had evolved into new species over time. [END PAGE] [BEGIN PAGE] Darwin considered this the best explanation for why such islands had many species that were found nowhere else, but that bore a resemblance to Investigation X.X.X 23 species on the nearest continental land mass. Table 1 lists some key observations regarding the species inhabiting the Galapagos Islands. Each observation is matched with Darwin’s corresponding hypothesis for all remote islands based on the theory that species evolve. Table 1 Species on Remote Islands Observations from the Galapagos Islands Darwin’s hypotheses regarding remote islands Many species of plants, birds, insects, and, in some cases, reptiles Only these kinds of organisms are able to reach remote islands by crossing large expanses of open ocean. No native amphibians and very few land mammals Amphibians and most mammals are unable to cross open ocean and will not occur on remote islands. Many unique species, found nowhere else on Earth Over time ancestral species will have evolved into new geographically isolated species. Unique species most closely resemble species on the nearest continental land mass Unique species are descendents of ancestral species from the nearest continental land masses and will exhibit some similarities. Testing Darwin’s Hypotheses [catch C07-P31-OB11USB; Size D; Permissions. Photo of the Galapagos or Hawaian islands showing volcanic nature/origin.] Figure 3 The Galapagos and Hawaiian islands were formed by volcanoes that rose from the bottom of the Pacific ocean. To learn more about the formation of these islands go to <catch web link> <CATCH: web link To learn more about the fascinating species that live on the Galapagos and other remote islands go to . . . .> [catch C07-P32-OB11USB; Size D; Research. Photo of an extinct bird species from Hawaii, e.g. the Black Mamo (Drepanis funera).] Figure 4 The Black Mamo (Drepanis funera), a species of honeycreeper, went extinct in about 1907. Of the original 41 species of Hawaiian honeycreeper, 17 are probably extinct, 14 are endangered, and only 3 species continue to have large healthy populations. Darwin’s hypotheses were tentative explanations for his observations. If correct, these hypotheses would apply to similar situations. The strength of any hypothesis is determined by how well it is supported by future tests and observations. In this case, the Hawaiian islands provide an excellent test case of Darwin’s hypotheses. Like the Galapagos, the Hawaiian islands were formed from volcanoes that rose directly from the ocean floor (Figure 3). They have a wide range of habitats and have never been connected to any other land mass. An examination of the native species of Hawaii supports Darwin’s hypotheses. There are no native amphibians or mammals with the exception of bats and sea lions. There are many species of unique plants, birds, and insects. Unlike the Galapagos, there are no native terrestrial reptiles. The only Hawaiian reptiles are marine species: a sea snake and five species of sea turtle. This difference can be accounted for by the fact that the Galapagos lie within 1000 km of the coast of South America, whereas the Hawaiian islands are much more remote – more than 4000 km from the coast of North America. No land reptile could be expected to survive such a long ocean crossing. <CATCH: web link> In testing a hypothesis, it is important to consider alternative explanations that might account for your findings. What if remote islands lack certain groups of organisms simply because these species are not able to live in such settings? Perhaps mammals and amphibians, for example, simply cannot survive on large oceanic islands. This alternative hypothesis has been put to the test when non-native species are introduced to islands. Introduced species have not only thrived in these new environments, but also have had a devastating impact on many native species. Rats, dogs, and pigs have wreaked havoc on native bird and tortoise populations. They eat the eggs and young of tortoises and ground-nesting bird species, which exhibit no fear or defensive behaviours. The impacts have been particularly damaging in Hawaii where an estimated 271 species have gone extinct since the arrival of Europeans in 1778 (Figure 4). Therefore, mammals and amphibians are, indeed, able to survive on remote islands once they are introduced and we cannot accept the alternative hypothesis. To date, Darwin’s hypotheses have been supported by the observations of life on all remote islands. [END PAGE] [BEGIN PAGE] RESEARCH THIS: INVESTIGATE DARWINS RESEARCH Investigation X.X.X 24 Skills: Researching, Predicting, Planning, Controlling Variables, Performing, Observing, Analyzing, Evaluating [catch Skills Handbook icon: t/k] Darwin was aware that not all seeds could have been carried to remote islands by the wind or birds. He hypothesized that some must have reached the islands by floating in ocean currents. If his hypothesis was correct, the seeds must have been able to withstand exposure to salt water for days or weeks on end. 1.t/k 2. 3. 4. A. B. C. Homologous and Analogous Features homologous features structures that share a common evolutionary origin but may serve different functions in modern species (e.g., bat wings and human hands) If all living things are related to each other, as the theory of evolution suggests, then we should expect to find evidence for such relationships by examining their anatomy. Darwin and others were struck by the numerous instances in which similar structures of two organisms could have entirely different functions (Figure 7). These homologous features puzzled Darwin who wrote: “What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?” Imagine an engineer being asked to design a robotic hand, a canoe paddle, and an aircraft wing, and choosing the same internal frame design for each device! [catch C07-F07-OB11USB; Size B; New. Image showing the forelimbs of different organisms that are each adapted to carry out very different functions yet they all possess very similar bone structures.] Figure 7 The forelimbs of these organisms are each adapted to carry out very different functions, yet they all possess very similar bone structure. It struck Darwin as unreasonable to think that finger bones would serve any useful purpose inside the stiff flipper of a whale. He also wondered why almost all mammals would have precisely 28 skull bones and 7 neck bones, regardless of the size of their skull or length of their necks. If species had been created in their present forms, why would the skull of a whale have the same number of bones as the skull of a mouse, and why would the giraffe not be given more neck bones than mammals with the shortest of necks? Indeed, why were the bones in all mammals, including bats, whales, horses and humans, so similar in number and arrangement (Figure 8, next page)? [END PAGE] [BEGIN PAGE] The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P33-OB11USB; Size B1; Research. Photo of a bat skeleton with outstretched limbs] [catch C07-P34-OB11USB; Size B1; Research. Photo of a human skeleton with limbs outstretched] Investigation X.X.X 25 Figure 8 All mammals have an almost identical number and arrangement of bones. This (a) tiny bat skeleton is very similar in many respects to that of (b) a human. Although Darwin had no understanding of chromosomes and genes, he knew that many traits were inherited from generation to generation. Darwin was also aware that artificial breeding of animals and plants could, over many generations, produce dramatic results. For example, he knew that dog skeletons had changed through the efforts of breeders. Darwin concluded that the homologous features he observed could be explained by evolution. Closely related species had homologous features because they shared a common ancestor. Over time original structures were modified as each species evolved. Closely related species share homologous developmental processes and patterns as well. In early developmental stages, the embryos of all vertebrates including humans, chickens, and fish possess a short bony tail (Figure 9). Human embryos also have gill slits even though, as adults, we do not have gills. [catch C07-F08-OB11USB; Size B; New. Illustration of embryo comparison between a fish, a salamander, a tortoise, a chick, a rabbit, and a human] Figure 9 The embryos of all vertebrates share many homologous features including tails and gill slits. [END PAGE] [BEGIN PAGE] Evolutionary relationships can also account for the observed differences in the structure of analogous features – features that perform similar functions. For example, the eyes and wings of flying insects serve the same function as the eyes and wings of flying birds yet are completely different in structure. Insects and birds are only distantly related and have evolved these features quite independently of each other. Vestigial Features and Anatomical Oddities What would you say if you discovered a fish with eye sockets but no eyes, or a running animal with toes that never touch the ground? These species would be displaying vestigial features – features that no longer serve the function they do in similar species. Several species of cave fish in the family Amblyopsidae Investigation X.X.X 26 analogous features structures that perform the same function but are not similar in origin or anatomical structures For example bird and insect wings live in perpetual darkness (Figure 10). They have no eyes or tiny vestigial eye. A number of mammals, including pigs, horses, and dogs, possess vestigial toes that serve no useful purpose (Figure 11). [catch C07-F09-OB11USB; Size B; New. Diagram comparing the toes of a dog, pig, and a horse showing their vestigial toes in blue] vestigial features rudimentary and nonfunctioning, or only marginally functioning structures that are homologous to fully functioning structures in closely related species [catch C07-P35-OB11USB; Size D; Research. Photo of a blind cave fish showing its empty eye socket. Photo must be of the family Ambylopsideae] Figure 10 t/k Figure 11 Dogs have a vestigial toe or “dew claw” on each front limb. The toe serves no useful function. Pigs have two welldeveloped toes and two vestigial toes that hang behind them. Horses have one greatly enlarged toe. The others are vestigial or missing entirely. Vestigial toes are shown in blue. There are many striking examples of vestigial features and anatomical oddities. For example, the upland goose and frigate bird have webbed feet but never enter the water. Some large snakes and whales have vestigial hip bones, which are homologous to the hip bones that support the hind limbs of other vertebrates (Figure 12). [catch C07-F10-OB11USB; Size B; New. Image of a silhouette of a whale showing the internal bone structure clearly. ] Figure 12 Many species of large whale have vestigial hip bones. [END PAGE] [START PAGE] A fascinating example of an anatomical oddity is found in the nervous system of vertebrates. In fish, a particular nerve exits the brain and follows a short and direct pathway to a gill located close to the heart. In all mammals, the same nerve exits the brain but it follows an indirect path. The nerve passes close to the heart, but then travels back up the neck and enters the larynx, or voice box. In giraffes, the trip is quite lengthy: the nerve leaves the brain, travels the full length of the neck down to the heart and back again before entering the larynx. The distance from a giraffe’s brain to its larynx is a few centimetres, but the pathway travelled is more than four meters! Darwin recognized that such features were highly suggestive of an evolutionary past. Vestigial features could be explained as evolutionary baggage – features that, in an ancestor, had served a useful purpose, but had become useless or greatly distorted as the species had evolved. Humans also possess numerous vestigial features. You may have experienced goose bumps in a cool breeze or when you were watching a scary movie. Humans, like most mammals, have body hair. Each hair is attached below the surface of the skin to a tiny muscle. Goose bumps are the result of Investigation X.X.X 27 these tiny muscles contracting and lifting up the hair. For mammals with thick hair, this action serves two functions: in response to cold temperatures, it increases the insulation value of the hair making the animal warmer; and, in response to a threat, it makes the mammal look larger. For a deer on a cold winter day, this is a way of staying warm. For a cat confronted by a large dog, this is a way of looking large and menacing. For humans, raising our hair does nothing to keep us warm and certainly does not make us look any larger.<catch web link icon> Competition within Populations To learn more about human vestigial features, go to [catch Nelson web link banner] The anatomical features of different species, biogeography, and the fossil record provided Darwin with evidence that species had changed over time and that species appeared to share a common ancestry. Breeders of domesticated animals and plants repeatedly demonstrated that species could change by selecting individuals with favoured traits to be the parents of each new generation. Darwin wondered if nature, like human breeders, might be able to favour certain individuals in a population over others. He found the answer in October of 1838 while reading a mathematics paper on populations written by the Reverend Thomas Malthus, Essay on the Principle of Population. In his essay, Malthus showed that all populations were limited in size by their environment – and in particular their food supply. Whatever the conditions, populations could not continue to grow indefinitely. Darwin was struck by the implications this had for individuals within populations. Many species produced large numbers of offspring but not all will survive (Figure 13). There was a limit to the size of the population that the environment could support. The result would be competition for survival between members of the same species. The next two images will be placed side by side in the text measure. Should have the same orientation. [catch C07-P36-OB11USB; Size B1; Research. Photo of a pond with hundreds of frog or toad eggs] [catch C07-P37-OB11USB; Size B1; Research. Photo of a flower (goldenrod for example) with seeds still attached but ready to disperse.] Figure 13 Frogs and toads produce hundreds of eggs, but few will reach maturity. Similarly many plants produce thousand of seeds. [END PAGE] [BEGIN PAGE] Competition between individuals of the same species is intense because they are vying for the same resources. Consider a population of 1000 robins that returns to Ontario in the spring. These 1000 robins form breeding pairs that may lay two or three batches of eggs each summer. If they all hatched and survived, the robin population would jump from 1000 in the spring to more than 5000 by the end of the summer. Of these 5000 robins, only about 1000 will return the next spring. Under these conditions, only one out of every five robins survives each year. Darwin wondered if the environment might be favouring certain individuals in this struggle for survival. FORMATTER: PLEASE SET AS 2 COLUMNS USING FULL PAGE WIDTH MINI INVESTIGATION: THE ELEPHANT PROBLEM Skills: [t/k] [catch Skills Handbook icon: t/k] Species that produce large numbers of offspring experience intense competition. Darwin wondered if this applied to even the slowest breeding populations like that of the elephant. His question is known as “the elephant problem.” In this activity you will compare the breeding potential of different species and populations sizes that would result if there was unlimited growth. Table 1 includes sample estimates of changes in population size for two different situations: a) under natural conditions and b) based on the assumption that all offspring live and reproduce under ideal conditions with no competition. For example, in the case of elephants, the latter value is based on the assumption that all elephants live to be 90 years old and each female has 6 offspring in her lifetime. Investigation X.X.X 28 1. Examine Table 1 and compare the initial population sizes with the estimated final population sizes. Note that under natural conditions populations often remain relatively stable over modest periods of time. (a) Calculate the percentage change in the population size. 2. Compare the initial population sizes with the final population size if there was no competition (b). Calculate the percentage change in the population sizes. A. What might cause a change in population size under natural conditions? B. How do these data provide evidence that species do not live under ideal conditions? C. Choose one species from Table 1 and conduct online research to determine some of the resources they require in order to survive (such as types of food, space, shelter). Which of these resources do you think would cause the greatest degree of competition between individuals of the same species? D. Imagine a dog breeder that makes a living selling champion show dogs. Do think the breeder would attempt to produce the maximum number of pups each year? What might be the disadvantages and advantages of doing so? Table 1 Population Potential Species Initial population Generations and a) Final population b) Final population elapsed time under natural under ideal conditions conditions Elephant 100 5 generations 84 24 300 300 years Robin 100 5 generations 10 years 120 3.3 million Deer Mouse 100 5 generations 10 years 96 320 million Starfish* 2 1 generation 5 years 2 10 billion *female starfish of some species can produce 2 billion eggs per year Assessing the Evidence Darwin spent more than twenty years gathering and examining every shred of evidence he had on the question of whether species had evolved or had been created in their present forms. In the end he was convinced that the preponderance of evidence was undeniably in support of the evolution of species but he also knew that his ideas would be controversial and conflict the most commonly held religious beliefs of society. Many other scientitists, including Linnaeus, Lamarck, and his own grandfather, believed species were not immutable. What set Darwin apart was the great insights he had gained while amassing the evidence. Darwin not only believed that species had evolved but believed he had theory that could explain how they evolved. In the next section you will learn the circumstances leading up to Darwin’s publication of On the Origin of Species and be introduced to his famous and elegant theory [END PAGE] [BEGIN PAGE] 7.4 SUMMARY • Evidence from biogeography provides compelling evidence that remote islands are populated by species that evolved from species that arrived there from the closest major land mass. • Patterns in embryonic development provide evidence of the evolutionary relationships between species. • The structures of numerous anatomical features provide strong evidence that they have evolved from an original, homologous structure. • Vestigial features are rudimentary structures that once performed important functions in ancestral species. • All species produce far more offspring than can survive to reproduce. This results in competition for resources between members of the same species. 7.4 QUESTIONS 1. Which of the following would you expect to find on remote islands? Explain your reasoning: [K/U, T/I] (a) a variety of hummingbirds OR a variety of larger seed eating birds Investigation X.X.X 29 (b) large lizards OR large mammals (c) some species that are genetically similar OR most species that are genetically very distinct. (d) species found now where else on Earth OR species that are also found on other remote islands. 2. The coqui frog was accidentally introduced to Hawaii in 1988 where it has no natural enemies. The population has risen dramatically and the frogs now pose a threat to native species, particularly insects and spiders. If these frogs are so successful why are there no native frog species on these large islands? [T/I, A] 3. Which of the following pairs represent homologous features and which represent analogous features? Explain your answers. [A] (a) a lobsters claw and the hand of an ape (b) the wing of a bat and the wing of a bird (c) the eyes of a fly and the eyes of a hawk (d) the tusks of an elephant and the teeth of a mouse (e) the webbed feet of an otter and the fins of a fish 4. Explain how the bones, arranged in a pattern of five toes, within dolphin flippers provide evidence of evolutionary change. [K/U, A] 5. The brown tree snake, Boiga irregularis, was introduced to the remote Pacific island of Guam sometime shortly after World War II. Do research to answer the following: [T/I, A] (a) What native species have been lost or threatened by this snake? (b) How might the loss of these species influence the entire ecosystem on the island? (c) How might an understanding of evolution enable scientists to predict which species might be most vulnerable to invasive species? 6. For each of the following vestigial features state the likely original function of the structure and suggest a reason that it may be become vestigial: [K/U, A] (a) the muscles and hairs that cause goosebumps in humans (b) short wing “stubs” in some insects like earwigs (c) webbed feet in frigate birds that never enter the water (d) rudimentary hip bones in some whales and in some large snake species 7. Describe the evidence of evolution revealed by the embryonic development of different species. [K/U] 8. Explain how Darwin knew that competition always occurs between individuals of the same species. Include a numerical example to illustrate your answer. [K/U T/I] [end page] Investigation X.X.X 30 [BEGIN PAGE; 4 pages] 7.5 [catch C07-P38-OB11USB; Size D; Research. Photo of the cover page of the first edition of Darwin’s On the Origin of Species] Figure 1 The cover page of the first edition of Darwin’s On the Origin of Species. To learn more about Alfred Russell Wallace and his many contributions, go to <catch Nelson web link banner> natural selection the way in which nature favours the reproductive success of some individuals within a population over others; the “Theory of Evolution by Natural Selection” explains how the process of natural selection results in the evolution of species On the Origin of Species Darwin’s On the Origin of Species was published in 1859. This book not only described convincing evidence that species had evolved, but it also proposed a theory of how species evolve. Darwin had formulated his theory much earlier. In 1844, Darwin wrote to his friend, Sir Joseph Hooker, declaring: “At last gleams of light have come, and I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable. ... I think I have found out ... the simple way by which species become exquisitely adapted to various ends.” In the same year, Darwin prepared a 231-page outline of his theory and gave it to his wife with instructions that it be published should he die unexpectedly. Aware that any theory of evolution would be controversial and rigorously challenged, Darwin continued to gather evidence and look for flaws and weaknesses in his own reasoning. His intention was to publish what he referred to as his “Big Book” on evolution. By June 1858, when he had written a quarter of a million words, he received a fateful letter from a brilliant young biologist working in Malaysia. In the letter, Alfred Russell Wallace outlined his own theory of how species evolved. His theory was almost a perfect match to Darwin’s. The young Wallace, with little evidence, was anxious to publish a theory that he had thought about for only a few days. Darwin, having spent twenty years amassing evidence and developing the same theory, had been unwilling to publish. Lyell and Hooker convinced Darwin to submit a paper along with Wallace’s at a meeting of the Linnean Society on July 1, 1858. The papers were of interest to scientists of the Linnean Society but went unnoticed by the public. A year and half later Darwin published a detailed account of his theory in a 502-page book entitled On the Origin of Species by Means of Natural Selection or The Preservation of Favoured Races in the Struggle for Life (Figure 1).The book sold out on the first day. <catch web icon> The Theory of Evolution by Natural Selection Although Darwin had been hesitant to publish, he was extremely confident in his theory that species had evolved by a process he called natural selection. Darwin described natural selection as the way in which the environment, or nature, favours the reproductive success of certain individuals over others. Evolution was simply the result of natural selection occurring over many generations. Darwin’s reasoning is illustrated in Figure 2. Formatter flow chart should be entire page width [catch C07-F11-OB11USB; Size B; New. Art of a flowchart showing how observations led to inferences which led to the Theory of Natural Selection for Darwin.] Figure 2 Darwin’s theory of evolution by natural selection was powerful because it was based on five key observations which were well established and undeniable. Darwin realized that together, they gave rise to two logical inferences and provided a mechanism for evolution. [END PAGE] [BEGIN PAGE] Darwin’s key observations were undeniable: all healthy populations produced far more offspring than could survive and reproduce; and, Investigation X.X.X 31 survival of the fittest a phrase that has been used to describe the process of natural selection; considered misleading and no longer used by biologists adaptation a characteristic or feature of a species that makes it well suited for survival and or reproductive success in its environment. individuals exhibited heritable variability. Darwin believed that, under these conditions, some individuals would have a better chance of success than others. A faster cheetah would surely be more likely to catch prey than a slower cheetah and a stronger male lion would be more likely to defend and mate with a pride of females. If this were true and these differences were inherited, then the traits of the favoured individuals would become more common in the next generation. Faster cheetahs and stronger lions would have more offspring than slower and weaker individuals of the same species. Indeed, Darwin’s theory was so simple and elegant that his friend and eminent zoologist Thomas Huxley exclaimed, “How extremely stupid not to have thought of if myself!” A contemporary of Darwin, Herbert Spencer, used the phrase “survival of the fittest” to describe the process of natural selection. Although Darwin himself thought the expression could be a useful synonym, it can be quite misleading. You might consider an individual that lives a long life but is unable to reproduce as physically “fit,” but the individual would pass on no genes to the next generation. Such an individual would not be fit with respect to Darwin’s theory of natural selection, or Spencer’s definition. As you will learn in Chapter 8, the key to natural selection lies in its ability to favour reproductive success. The theory of evolution by natural selection could be extended to virtually every biological characteristic or adaptation. Figure 3 shows a number of adaptations and the selective advantage they represent. Darwin understood that with a diversity of environments, the process of natural selection acting over thousands of generations could produce an unlimited variety of species. The next 7 images will go side-by-side across entire page width. Place text with each photo. Arrange however works best. Photos should have the same orientation. [catch C07-P39-OB11USB; Size C3; Research; Photo of a polar bear with ice/snow background.] catch C07-P40-OB11USB; Size C3; Research. Photo of Galapagos finch, any species, showing their large bill.] [catch C07-P41-OB11USB; Size C3; Research. Photo of an anteater with tongue visible of digging in termite/ant mound.] [catch C07-P42-OB11USB; Size C3; Research. Photo of male moose with antlers.] [catch C07-P43-OB11USB; Size C3; Research. Photo of elephant seal in water if possible.] [catch C07-P44-OB11USB; Size C3; Research. Photo of cacti, any species, showing thick stem with sharp needles.] [catch C07-P45-OB11USB; Size C3; Research. Photo of pine tree bark.] Figure 3 Individual organisms possess traits that give them a selective advantage. or [t/k] Evaluating the Theory Darwin had proposed a revolutionary theory in biology that challenged not only the established science of the day, but also currently held beliefs and teachings of a large fraction of society. Darwin knew that all scientific theories must be explanatory, have predictive powers, and be testable. We will examine these below. EXPLANATORY POWER As you learned in previous sections, Darwin had amassed a great deal of evidence from biogeography, the fossil record, the anatomical features of different species, and artificial breeding. Consider how Darwin might have applied his theory of natural selection to explain the evolution of large-billed finches on the Galapagos Islands (Figure 4, next page). [END PAGE] [BEGIN PAGE] [Formatter: This will be a 2x2 frame piece of art. Should take about ½ page or slightly more.] [catch C07-F12-OB11USB;Size A; New. Description of art to come. Captions to be placed below each frame, include: (a) An ancestral population of finches with medium-sized bills are the first seed-eating birds to arrive on the Galapagos Investigation X.X.X 32 [catch C07-P46-OB11USB; Size D; Research. Photo of a large ground finch of the Galapagos.] Islands. They specialize in eating medium-sized seeds. With no initial competition, the finches establish a growing population on a small island with a variety of plants, some with medium seeds but most with larger seeds. (b) The population grows to a size where the number of finches has reached the limit of their food supply. Each year many eggs are laid and hatched, but the island cannot support all the birds. The birds are not all alike – like any species, they exhibit variation. Some birds have slightly larger, and some slightly smaller than average bills. (c) Most of the birds must compete for the same medium-sized seeds, but any bird born with an unusually large bill is able to also feed on the larger seeds. These particular birds have little or no competition have ample food available to them. Darwin would say that the environment favours, or selects, these larger-billed birds. These larger-billed birds, being healthier, lay more eggs on average. Their young are more likely to be born with larger bills. (d) As this process is repeated generation after generation, the average bill size of the birds continues to increase (Figure 5). This is evolution by natural selection. Had medium-sized seeds been more common than larger seeds, the advantage of the larger bill might have been offset by the energy needed to grow the bill and or disadvantages in reaching and manipulating the medium sized seeds. Figure 5 The large-billed ground finch of the Galapagos islands evolved from an ancestral species that possessed a much smaller bill. Figure 4 Evolution of large-billed finches on the Galapagos Islands. or [t/k] Critics of Darwin questioned the source of variability in characteristics. Although small increases in bill size seemed possible, they wondered how an ancestral giraffe with a short neck could ever evolve into a modern longnecked giraffe. Although Darwin could not have foreseen the discovery of DNA and the role that mutations play in producing variation, he did have evidence from animal breeding that suggested such dramatic changes were possible. Although the source of the variation was a mystery, Darwin argued that if dogs could be so altered in a few hundred years of artificial selection, why could nature not accomplish even greater change in thousands and even millions of years of natural selection. PREDICTION The theory of evolution by natural selection enables scientist to make predictions about how species may change over time. Many of these predictions are associated with changing environments. For example, the theory of evolution predicts that species will evolve in response to climate change because different environmental conditions will favour different traits. Over time, bird species may change the timing of their migration and plants may adapt to warmer or drier conditions. Such changes are already being documented. The theory of natural selection also predicted the evolution of antibiotic resistance in bacteria and pesticide resistance in insects. Darwin made predictions regarding the fossil record of humans. Based on the distribution of the living great apes, he predicted that fossils of the most primitive human ancestors would be found on the African continent. Darwin’s predictions have come true. [END PAGE] BEGN PAGE] TESTING AND FALSIFICATION Darwin also knew that to be scientific, a theory must have the potential to be falsified. This means that a scientific theory must be testable — there must at least be the possibility of it being proven wrong. For example, the theory of gravity meets this scientific standard because it could be falsified by observing apples “falling up.” The fact that we never find such evidence adds strength to Investigation X.X.X 33 Formatter: Place next to Testing & Falsification heading. INVESTIGATION 7.6.1 Natural Selection (p. XXX) You will design and conduct a controlled experiment to test Darwin’s theory in a simulated predator-prey relationship. the theory of gravity. Table 2 illustrates a few of the kinds of evidence that could falsify the theory of evolution as well as the evidence that currently exists. Table 2 The Potential for Falsification Hypothetical observations with the potential to falsify Darwin’s theory Actual observations and evidence Amphibians and large land mammals on remote oceanic islands No native amphibians or large land mammals have ever been discovered on remote oceanic islands. Fossils of complex organisms found in the oldest fossil deposits Of millions of fossils, none contradict the predicted pattern of increasing complexity over time. Complex organisms with no vestigial features All organisms that have been studied in detail exhibit many vestigial features. Species thought to be closely related that share no homologous features with each other All organisms that have been studied in detail exhibit many homologous features with other closely-related species. Darwin knew that if evolution had not occurred, if species had not changed over time, it should be easy to find falsifying evidence. His confidence in the theory was greatly strengthened by the complete absence of falsifying evidence. 7.5 SUMMARY • Darwin’s theory of evolution by means of natural selection explains how the environment acts to favour the reproductive success of individuals with certain heritable traits over others. • Darwin’s theory of evolution by means of natural selection is able to explain how an adaptation can arise. • Darwin’s theory of evolution by means of natural selection can be used to make predictions about the future evolution of species. • Darwin’s theory of evolution by means of natural selection is a testable scientific theory. 7.5 QUESTIONS 1. (a) What evidence from Darwin’s personal life suggest he did had developed his theory but was very hesitant to make it public? [A] (b) Why do you think Darwin might not have wanted to publish his ideas? 2. (a) How did Wallace influence Darwin’s decision to publish? [K/U, A] (b) Do you think Wallace should be given as much credit as Darwin for the theory of evolution by natural selection? Why or why not? 3. Match Darwin’s inferences, on the left, with his observations, on the right. [K/U] [formatter: DO NOT format this in a table; format as you would a matching Q in the chapter review] I. Some individuals will inherit characteristics A. Populations produce more offspring than can that are of benefit and increase their chance of survive to adulthood reproductive success B. Individuals of all species show variability II. Individuals of all species are in competition for C. Resources for any species is limited resources D. Populations do not continue to grow forever E. Some variability is heritable 4. Use one or two examples to explain what Darwin meant by the term “selection.” [K/U] 5. A male walrus lives to be 20 years old and successfully mates with 18 females during its life. A second male only lives to be 10 years old but mates successfully with 44 females. Which male has natural selection “favoured?” Explain your reasoning. [K/U, A] 6. Suggest a probable selective advantage for each of the following traits: [A] (a) the clear wings of many flying insects (b) long tongue of a chameleon (c) the tendrils of climbing plants (d) sweet-tasting and brightly coloured fruits (e) eel body shape (f) dramatic colouration of the non-venomous false coral snake 7. Outline a set of hypothetic steps that might take place as a species of bird evolves a smaller bill after reaching a remote island. [K/U, A] 8. How did the absence of falsifying evidence increase Darwin’s confidence in his theory? [K/U] 9. When he published On the Origin of Species, Darwin was still planning to write a much more detailed “Big Book” on evolution, Darwin had originally titled his book An Abstract On the Origin of Species . . . His editor convinced him to remove “An Abstract.” An abstract is a short summary of a larger scientific document. [T/I, A] (a) What does this suggest about Darwin’s approach to science? (b) Darwin never completed his “Big Book.” Go online and to learn about books that Darwin did write in the years following the Origin. 10. [a RT related to curriculum 2.3 in the section questions.] [END PAGE] Investigation X.X.X 34 Investigation X.X.X 35 [BEGIN PAGE; 6 pages] 7.6 The Modern Theory of Evolution Evolutionary biology has made tremendous advances since Darwin. The science of genetics has allowed scientists to uncover the mechanism of heredity and the actual source of biological variation. The fossil record is now extensive, and our ability to interpret fossil data has been greatly enhanced by remarkable advances in the science of geology. These and other advances in science have not only confirmed Darwin’s theory, but have greatly enhanced our understanding of the fundamental biology of all living things. Among these advances are: our ability to accurately date the age of Earth; our discovery of the source of variations within species; and new sources of powerful evidence in support of evolution. The Age of Earth Formatter: Place this beside Age of Hearth heading INVESTIGATION 7.7.1 A Walk Through Time (p. XXX) You will investigate the timing of major events in Earth and Human history using a physical time scale model. Until well into the 19th century many people, including some scientists, believed that Earth was less than 6000 years old, and that it had not changed significantly during that time. The mountains, coastlines, and rivers had always been the way they were at the present time. They believed that in a few thousand years, processes like erosion had not had enough time to significantly alter the physical surface of Earth. This belief was extended to living organisms. They believed that species never changed and that species that are present today had always been present. These widely held beliefs began to change early in the 20th century when the emerging sciences of palaeontology and geology started to cast serious doubt on the belief in a young Earth. Today there is a wide scientific consensus that Earth is extremely old. Modern geology, physics, and astronomy provide compelling evidence that Earth and our solar system are more than 4.5 billion years old, and that the universe is approximately 13 billion years old. Evidence for these values comes from many different sources, all of which are in close agreement. The evidence is largely a product of recent advances in technology and understanding. Radiometric Dating radioisotope atoms with an unstable nucleus that are capable of undergoing radioactive decay parent isotope changes into a daughter isotope as radioactive decay occurs daughter isotope an isotope formed as a result of radioactive decay Paleontologists are able to use radioisotopes to obtain very precise estimates of the ages of the rocks that contain them. Radioisotopes are atoms that undergo radioactive decay – a process in which the nucleus of an atom changes and releases a subatomic particle. The nuclei of these atoms are unstable and release subatomic particles changing from one form, the parent isotope, into another, the daughter isotope. For example, most carbon atoms have six protons and six neutrons and are not radioactive. However, a small fraction of carbon atoms are radioactive. They have a nucleus containing six protons and eight neutrons. When these radioactive carbon 14 (14 C) isotopes undergo decay, they release a high energy particle and one of the protons changes to a neutron. The daughter isotopes are now nitrogen atoms (14 N), each containing seven protons and seven neutrons. The technique of radiometric dating is complicated but is based on a comparison of the ratio of parent to daughter isotopes in rock formations. Radioisotopes undergo decay in a very precise way. The length of time that it takes for half of any amount of a particular radioisotope to decay is a constant. [END PAGE] [BEGIN PAGE] [not a new para; just the same para continued on the next page]This value, called the half-life, is the time it takes for exactly 50% of a parent isotope to decay into a daughter isotope (Figure 1). It then takes an Investigation X.X.X 36 half-life the time required for half the quantity of a radioactive substance to undergo decay; the half-life is a constant for any given isotope additional half-life for the remaining amount to be reduced by half again, and so on. Physicists have determined the half-life of all naturally occurring radioisotopes. [formatter: please centre art in text measure] [catch C07-F13-OB11USB; Size C2; New. Graph showing the half-life of radioactive decay.] Figure 1 During each half-life of radioactive decay, 50% of a parent isotope decays into a daughter isotope. The result is a quantitative, predictable relationship between the ratio of parent-to-daughter isotopes and elapsed time. The Modern Synthesis modern synthesis the modern theory of evolution that takes into account all branches of biology gene pool the complete set of all alleles contained within a species or population [catch C07-P47-OB11USB; Size D; Research. Photo of a curly haired poodle] Figure 2 Perhaps hundreds of generations ago a dog was born with a single base mutation in a gene coding for a hair protein. The mutation resulted in very curly hair - a trait that was selected for by breeders and is now common in number of breeds including poodles and many terriers. Darwin’s theory of evolution by natural selection could account for how species evolve but could not explain the actual source of variation. The modern synthesis in evolutionary biology resolved this weakness in the theory by combining the principles of Darwin’s theory of natural selection with the new science of genetics and other fields of biology. We now know that inheritance involves the passing on of genes from parents to offspring. Genes are sequences of DNA that code for heritable traits and different forms of the same gene are called alleles. Individuals vary in their traits because they inherit different combinations of these alleles. Natural selection acts to favour some genetic combinations over others. Darwin defined evolution as changes in the inherited traits of a species over time. Today, biologists define evolution as changes in the gene pool of a species over time. A gene pool consists of all the alleles of all individuals that are currently present in a particular species or population. Mutations: The Source of Variation All species exhibit genetic variation. Different individuals have different combinations of the many alleles that are already present in the population. Sexual reproduction recombines, or shuffles, these alleles and produces an almost unlimited number of combinations. New or altered traits arise when new alleles and genes are produced by mutation and acted upon by natural selection. A genetic mutation is a change in DNA. The bases that make up DNA may be switched or lost, and or new bases may are be inserted (Figure 2). Mutation events can also result in an individual having duplicate copies of genes. Duplication events are usually the result of mismatches during crossover in meiosis. A misalignment of the chromosomes during crossover causes an unequal exchange – transferring a portion of one chromosome to another (Figure 3). The transferred portion of the chromosome is likely to contain many genes. [formatter: please centre art in text measure] [catch C07-F14-OB11USB; Size C2; New. Illustration of a mismatched crossover event showing the duplication of genes.] Figure 3 Cross over errors, a form of mutation, can result in one sister chromatid having a duplicated portion of a chromosome, while the other chromatid will be missing a portion of the chromosome. [END PAGE] [BEGIN PAGE] A gamete that receives a chromosome that is missing a section will have a low chance of survival, while the gametes that receive a chromosome with duplicated genes are often viable. In fact, having extra copies of genes can be beneficial. For example, a recent study compared the number of copies of a certain gene among people of Japanese descent having a diet that is Investigation X.X.X 37 traditionally high in starch, with those of Amazon rainforest dwellers that have a low-starch diet. This gene is responsible for the production of amylase, which is the enzyme that breaks down starch. The people of Japanese descent had multiple copies of the amylase gene – enabling their cells to produce more of the digestive enzyme. Gene duplication is an important type of mutation because it is a source of new genes. The extra copy of the gene is free to mutate and potentially gain a new function. The gene copies resulting from duplications can also be altered through further mutation. Many genes code for vitally important proteins. If a mutation in a gene results in a new protein that can no longer perform a vital function, the organism may die – even if the new protein might be beneficial in some other way. However, the same mutation occurring in an extra” copy of the gene might result in the creation of a new and potentially beneficial protein. The duplication and mutation of gene copies can result in entire “families” of closely related genes. For example, four human genes – three involved in colour vision and one for night vision – are all thought to have been produced from a single ancestral gene. The Effects of Mutations [TOP ALIGN WITH “THE EFFECTS OF MUTATIONS”] LEARNING TIP Consider the Numbers Natural populations are often extremely large. A small section of forest can be home to millions of black flies while a soccer field is home to millions of grass plants. Even if the mutation rates for individuals are relatively low, the number of mutations within a population is very large. Table 1 Mutation and Evolution Factor Influence on Evolution Beneficial mutations Relatively rare but are favoured by natural selection and tend to accumulate in populations over time Harmful mutations More common than beneficial mutations but are selected against and therefore have no influence of populations Duplication Often neutral and so mutations do not immediately benefit the individual but provide a source of new genetic material with the potential to evolve into new genes Mutation rates Relatively low for As you learned in Section 7.1, mutations can be neutral, beneficial, or harmful. Most mutations are neutral because they occur in non-coding portions of DNA and therefore produce no visible change in an individual. The environment does not favour or select against individuals with neutral mutations. Beneficial mutations, which give the individual an advantage, are selected for by the environment. Therefore we would expect beneficial mutations to accumulate over time because they increase the reproductive success of individuals. For example, mutations that have allowed some plants to produce colourful flowers and attract pollinators have been beneficial to those species and these new genes have become widespread. Harmful mutations may make an organism less able to resist disease or avoid predators, or less efficient at obtaining food. Regardless of the reason, individuals with harmful mutations are less successful at reproducing and therefore harmful mutations will tend to disappear. MUTATION RATES A common misconception is that mutations are rare. There is a very good reason for this. When chromosomes, consisting of strings of DNA bases, are replicated, the error rate is typically less than one mutation in a million bases. Duplications, inversions, deletions, and other mutations are also relatively uncommon events. However, organisms have genomes comprised of millions and often billions of DNA bases. In addition, populations often consist of millions of individuals. Individual mutation rates are very difficult to estimate, but recent studies suggest that species with large genomes are likely to have mutation rates averaging more than one per individual. The same studies suggest that humans, with genomes consisting of billions of bases, may average 20 or more mutations per individual. Even if these are almost always neutral, the numbers are staggering: the human population – approaching 7 billion people – is carrying around well over 100 billion genetic mutations. A similar high incidence of mutation occurs in all species with large populations. Table 1 summarizes key relationships between mutations and evolution. [END PAGE] [BEGIN PAGE] Homologous Genes and Pseudogenes Investigation X.X.X 38 individuals but can be numerous in populations over all [END PAGE] In Section 7.5 you observed that closely related species share many homologous features. All mammals, for example, have similar numbers and arrangements of bones because they have inherited this pattern from a common ancestor to all mammals. Similarly, closely related species inherit homologous genes. These genes, inherited from a common ancestor, mutate and evolve over time. The degree of similarity between homologous genes provides good evidence for the degree of relatedness between species. The more closely related two species are, the more similar we would expect their homologous genes to be. Figure 4 compares a very small portion of a DNA sequence from a number of species. [formatter: please centre art in text measure] [catch C07-F15-OB11USB; Size C2; New. Figure showing the sequences of bases on the DNA of a cow, deer, whale, hippo, pig, and rat.] Figure 4 The letters represent the sequence of bases on the DNA of these species. All sequences code for a short portion of a homologous gene. The more closely related the species the greater the similarity. Coloured letters highlight the differences from those of the Rat sequence – the least closely related mammal. pseudogenes vestigial genes that no code for a functioning protein; most species have many pseudogenes Species also have pseudogenes –genes that have undergone mutations and no longer serve a useful purpose. Like vestigial anatomical features, pseudogenes represent what is remaining of a gene that once served a useful purpose. For example, dolphins, like all mammals, breathe through their nose, but unlike most mammals, have no need for a sense of smell in the air (Figure 5(a)). Dolphins are thought to have evolved from land mammals. Most land mammals have an excellent sense of smell. Mammals have approximately 1000 functioning olfactory receptor (OR) genes that code for the receptors that detect airborne chemicals. Dolphins have these same 1000 genes but only about 200 of them are functional. The remaining 800 or so are pseudogenes. Biologists suspect that after dolphins had evolved an aquatic lifestyle, their OR genes were of no value. Any mutations that made the genes dysfunctional would have been neutral and not been selected for or against. Over millions of years most of the dolphins OR genes have become pseudogenes. Pseudogenes, like vestigial features, are found in virtually all species. For example, the stomach of the duck-billed platypus has no chemical digestive function yet the platypus has three defective genes that code for the production of digestive enzymes normally produced by the stomach. This provides evidence that platypuses evolved from an ancestor with a stomach that released digestive enzymes coded for by properly functioning genes (Figure 5(b)). The next two images will be placed side by side across the text measure. Should have the same orientation. [catch C07-P48-OB11USB; Size B1; Research. Photo of a dolphin head shot in water] [catch C07-P49-OB11USB; Size B1; Research. Photo of a platypus] Figure 5 (a) Dolphins have many pseudogenes that are homologous to genes they no longer have a need for. They have hundreds of pseudogenes that once coded for a keen sense of smell. (b) The platypus has pseudogenes for the production of stomach enzymes – useful in ancestors that had a stomach. [END PAGE] Investigation X.X.X 39 [BEGIN PAGE] Modern Paleontology The last 100 years have witnessed many important fossil discoveries, which have enhanced and enriched our understanding of evolution. These have included fossils of early human ancestors, dinosaurs in western Canada, and primitive whales in Pakistan. In recent decades, paleontologists have unearthed spectacular fossils of feathered dinosaurs in China and have even been able to determine the colour of some their feathers. The distribution of fossils provided Darwin with important evidence for his theory of evolution. He discovered fossil remains of giant prehistoric mammals that were similar in form to present-day armadillos and sloths living in the same region. Such a pattern has now been documented in many locations around the world. Australia for example, is home to many fossils of primitive kangaroos, but has no fossils of mammals typical of other continents. Until the 1960s, the location of some fossils were quite puzzling. Particularly surprising was the discovery of fossils of the same species in Africa, India, and Antarctica – but nowhere else on Earth. Today the study of biogeography has been complemented by great advances in the study of plate tectonics and continental drift. Plate tectonics describes the movements of the Earth’s crust and accounts for many large surface features, such as mountains, as well as volcano and earthquake activity. Figure 6 illustrates the arrangement of some of Earth’s major land masses approximately 200 million years ago. Species’ distributions at that time were permanently captured in the fossil record. <CATCH: Web link> [catch C07-F17-OB11USB; Size B; New. Map of fossil location in Pangea.] plate tectonics the scientific theory that describes the large scale movements and features of the Earth’s crust WEB LINK Fossil Discovery To learn more about how fossils are discovered, extracted, and preserved, go to <catch Nelson web link banner> Figure 6 Fossil distributions of these four species match the arrangements of the Earths land masses at the time the species were alive. Fossils also show distinct patterns in time. The oldest fossil deposits contain only simple life forms. More recent fossil deposits contain species that are both more complex and more similar to present living species (Figure 7). Of the millions of fossils that have been recovered and carefully documented, not a single fossil has been found to contradict this underlying pattern. [END PAGE] [BEGIN PAGE] [FORMAT TWO COLUMNS; FULL PAGE MEASURE, INCLUDE 2 PHOTOS IN BOX] RESEARCH THIS: PUIJILA, THE YOUNG SEAL Canada has been home to many remarkable fossil finds. One of the most recent is that of Puijila darwini - a missing link Investigation X.X.X 40 [catch C07-F16-OB11USB; Size D; New. Illustration showing horse evolution and toes, based on sample below] Figure 7 [t/k] between prehistoric land mammals and modern seals (Figure 8). Puijila was discovered in Canada’s high Arctic by a team led by Natalia Rybczynski, a paleontologist with the Canadian Museum of Nature in Ottawa. Dr. Rybczynski ‘s efforts and success highlight the challenges and rewards of scientific discovery. In this activity you will have the opportunity to research this important fossil discovery and see how paleontologists literally put pieces of evidence together. and gain a rich understanding of life’s evolutionary past. The next two images will be placed side by side in the margin. Should have the same orientation. [catch C07-P50-OB11USB; Size C1; Research. Image of the Pujila fossil. Any “interesting” image from the Puijila web site would be good.] [catch C07-P51-OB11USB; Size C1; Research. Photo of the Haughton crater, Devon Island, Nunavut.] Figure 8 (a) The Puijila fossil and (b) the Haughton crater, Devon Island, Nunavut. Skills: Researching, Communicating, Observing, Analyzing, Evaluating 1. Go online to learn the details of the Puijila fossil discovery and analysis. 2. Research the details of Rybczynski’s field work including the particular challenges associated with working in the Arctic. 3. Research the scientific publication of the discovery. In which journal was the research published? A. Why was this particular fossil find so important? Why was this “missing link” of interest? [A] B. What anatomical features of Puijila indicate it was semi-aquatic? [T/I, A] C. New fossil species are given new names. How did Rybczynski’s team decide on a suitable name? [A] D. Describe the formation of the Haughton crater and why it is a good location for finding fossils. [T/I, A] E. Describe the events leading up to the discovery of the initial fossil and the later discovery of the skull fragment. [T/I] F. In which science journal was this discovery reported? There are thousands of different journals. What makes this one special? [T/I, A] G. Report your findings to the class. Consider putting on a short skit to reenact the fossil discovery. [C] Modern evolutionary biology is supported by the most recent advances and discoveries in molecular genetics, geology, and paleontology. This has enable scientists to understand the source of new variations within species, account for the unusual distribution of some fossils, and confirm predictions of the theory. As you will soon discover, the modern theory of evolution also has the power to explain the evolution of complex adaptations and structures and the evolution of entirely new species. 7.6 SUMMARY - the Modern Synthesis of evolutionary biology combined Darwin’s theory of evolution by natural selection with the science of genetics. - genetic mutation events provide a continuous supply of all new inheritable information and variation within a species. - Beneficial mutations are favoured by natural selection. - neutral mutations have no immediate influence on the success of an individual - harmful mutations are selected against – reducing their frequencies within a population - pseudogenes provide compelling evidence for evolution - the science of plate tectonics and paleontology have greatly enhanced our understanding of evolution 7.6 QUESTIONS 1. How might the daily experiences of people contributed to their belief in an Earth and species that don’t change? [A] 2. Approximately how old is Earth? What types of scientific evidence were used to arrive at this date? [K/U, A] 3. Describe the relationship between the following terms: [K/U, A] (a) parent isotope, daughter isotope, half life (b) evolution, gene pool, species (c) duplication, crossover, gene family 4. E. coli bacteria are extremely numerous (billions of E. coli cells are living inside you!) and reproduce extremely quickly. Geneticists estimate that every part of their DNA undergoes a mutation somewhere on Earth every day. What might this suggest about the ability of E. coli to evolve? [A] 5. Humans are one of a small number of mammals that is unable to synthesize vitamin C. Instead we obtain vitamin C in our diet. Humans have a pseudogene that is homologous to a gene involved in vitamin C synthesis in other mammals. [T/I, A] (a) Is the presence of this gene surprising? Why or why not? (b) What does it suggest about human evolution? 6. Modern lemurs are only found on Madagascar Island off the coast of southern Africa. However, fossils of ancient lemurs have been found thousands of kilometres away in India where there are no lemurs. Consult Figure X and provide a possible explanation for this finding. [T/I, A] 7. Copy the following DNA base sequences into your notebook. They are all short samples taken from appear to be matching chromosomes in closely related species. Compare the sequence in species A with that of Species B, and then compare the sequence of species A with that of species C. [T/I, A] Species A . . . . . GGTAA AACAG CCTTA AGCGCC . . . . . Species B . . . . . GGTAA CAACA GCCTT AAGCGC . . . . . Investigation X.X.X 41 Species C . . . . . GCTAA AACAG CCCCA AGCGGC . . . . . (a) Is there any evidence that one species experienced a single base “insertion” mutation? Explain. (b) Considering your answer in (a), which two species are probably more closely related? [END PAGE] Investigation X.X.X 42 [FORMATTER: Please format Inv in 2 columns, as per Design] [2pp total] 7.6.1 Controlled Experiment Natural Selection Some prey species are extremely well camouflaged. Darwin believed that the evolution of this trait was influenced by natural selection. If this is true, better camouflaged individuals should be “favoured” over less well camouflaged individuals and become more common in the population over time. In this investigation, you will design and conduct a controlled experiment to test Darwin’s theory in a simulated predator-prey relationship over a number of “generations”. SKILLS MENU Questioning Researching Hypothesizing Predicting Planning Controlling Variables Performing Observing Analyzing Evaluating Communicating Investigation X.X.X 43 Testable Question Can an environment favour the success of better camouflaged individuals in a predator-prey relationship? Hypothesis Formulate a hypothesis based on the testable question after considering options for your experimental design. Variables As you design your experiment, carefully choose your independent and dependent variables and decide which variables will need to be control. Experimental Design Your experiment must simulate a predator-prey relationship in which prey exhibit varying degrees of camouflage. There are many ways of designing and conducting such an experiment. Consider the following suggestions in your experimental design process: • Use simple objects with different colours or patterns as your prey items (such as pieces of paper or coloured candies,). • Use different coloured or patterned backgrounds for your environment (such as paper backgrounds or natural ground covers). • Use a student as the predator and give him or her a limited time interval in which to hunt prey. • Use the ratio of camouflaged versus non-camouflaged individuals that survive predation to determine the ratios of the following generation. For example, if there are 6 camouflaged individuals and 4 non-camouflaged individuals surviving from an initial population of 20 individuals of each, then the next generation should begin with a ratio of 6:4 (or 3:2) camouflaged to non-camouflaged individuals. • Go online to find more ideas on how to design your experiment. • Be sure to carefully consider how you will collect and record you data. How will you design your data tables? Equipment and Materials • Obtain materials as required for your design [Caution, DO NOT consume any food items used in your experiment] Procedure 1. Research and plan your controlled experiment. 2. Obtain teacher approval of your design and gather your needed equipment and materials. 3. Conduct your experiment. 4. Record your observations in an appropriate format. Consider graphing your results. Analyze and Evaluate (a) Identify the major variables that you measured and/or controlled in this investigation. Which variables were manipulated (independent) and which were responding (dependent)? (b) Prepare a formal lab report on this investigation. (c) Share your findings with other students in the class. How did your results compare with theirs? Apply and Extend (d) Real-world experiments of natural selection involving predator-prey relationships have been conducted on small islands in the Bahamas. Research and summarize the findings of these large-scale controlled experiments. (e) Do an internet search for extremely well camouflaged species. Share your findings with the class. (f) Try one or more online computer simulations of natural selection and or artificial selection. Explain how natural selection differs from artificial selection. [CATCH weblink] [catch web link banner] Investigation X.X.X 44 [FORMATTER: Please format Inv in 2 columns, as per Design] 7.7.1 Observational Study A Walk Through Time In this activity you will gain perspective on important events in both human history and the history of life on Earth. One timeline will be used to represent events in the past 12 000 years of human civilization while the other will represent major events during the past 4.6 billion years of Earth history. The data used in this investigation are based on historical references and the fossil record. SKILLS MENU Questioning Researching Hypothesizing Predicting Planning Controlling Variables Performing Observing Analyzing Evaluating Communicating Investigation X.X.X 45 Purpose To investigate the timing of major events in Earth and Human history using a physical time scale model. Equipment and Materials • • • • 50 m measuring tape (one per class) Human Civilization Event Cards (handout) Life on Earth Event Cards (handout) Data Table (handout) Procedure 1. When instructed to do so, all student groups will place their Human Civilization Event Card(s) at the appropriate positions along the same side of the tape measure according to the distance values indicated on the backs of the cards. 2. After all the cards have been placed on this scale, the entire class will “take a walk back through time” beginning at 0 m, which represents the present. Read and record the information from the events cards on your data table. 3. Next, place your Life on Earth Event Card(s) at the appropriate positions along the opposite side of the tape measure. 4. After all the cards have been placed on this scale, the entire class will “take a walk forward through time” beginning at the end of the tape (50 m). Read and record the information from the events cards in your data table. Observations Record all observation in the Data Table provided. Analyze and Evaluate (a) Did the historic timing of any of the Human Civilization events surprise you? Explain. (b) Did any events demonstrate civilization made rapid progress from 1400–1900? (c) Did any events suggest civilization made very slow progress between 1400–1900? (d) Did the historic timing of any of the major Life on Earth events surprise you? Explain. (e) For approximately how long did prokaryotes inhabit the Earth before any eukaryotes were present? (f) Approximately how long did life exist on Earth before multi-cellular life arose? (g) Based on these models, would you consider the following events to be “ancient” or “recent?” i) first evidence of photosynthesis ii) presence of life on land iii) appearance of dinosaurs iv) extinction of dinosaurs v) appearance of apes vi) first humans (h) Do any of the events demonstrate or suggest that major change in life on Earth is slow? (j) Do any of the events demonstrate or suggest that such change is fast? Apply and Extend (h) In this investigation you used a linear model to represent time. Research and report on other ways of depicting the timing of events in Earth’s history. [CATCH weblink] [catch web link banner] [END 2pp] 7.1 Biological Change Over Time 46 [new page] [Formatter: place the following features in 2 columns, as per design] Chapter 7 Summary Summary Questions 1. Create a study guide based on the Key Concepts listed at the beginning of the chapter on page XXX. For each point, create three or four sub-points that provide further information, relevant examples, explanatory diagrams, or general equations. 2. Return to the Starting Points questions at the beginning of the chapter on page XXX. Answer these questions using what you have learned in this chapter. Compare your answers with those that you gave at the beginning of the chapter. How has your understanding changed? What new knowledge and skills do you have? Vocabulary artificial selection fossil amber paleontology radioisotope parent isotope daughter isotope half life immutable catastrophism uniformitarianism biogeography homologous feature analagous feature vestigial feature natural selection survival of the fittest modern synthesis gene pool neutral mutations beneficial mutations harmful mutations pseudogenes Career Pathways Grade 11 Biology can lead to a wide range of careers. Some require a college diploma or a B.Sc. degree. Others require specialized or post-graduate degrees. This graphic organizer shows a few pathways to careers mentioned in this chapter. 1. Select two careers, related to Evolution that you find interesting. Research the educational pathways that you would need to follow to pursue these careers. What is involved in the required educational programs? Prepare a brief report of your findings. 2. For one of the two careers that you chose above, describe the career, main duties and responsibilities, working conditions, and setting. Also outline how the career benefits society and the environment. [catch C07-F18-OB11USB; Size A; MPU. Careers graphic organizer. MPU C04-F21-OB11USB.] [end page] 7.1 Biological Change Over Time 47 [new page] Chapter 7 Self-Quiz [QUESTIONS TO COME] [end page] [new page – 6 pages begin] Chapter 7 Review [QUESTIONS TO COME] [end 6 pages] 7.1 Biological Change Over Time 48