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Evolution Change Over Time “There is no ‘Great Plan’out there to conform with the evolutionary theory, just organisms struggling to pass their genes on to the next generation. That’s it.” Clown, Fool, or Simply Well Adapted? • All organisms have evolutionary adaptations – Inherited characteristics that enhance their ability to survive and reproduce • Ex. The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment • Large, webbed feet help propel the bird through water at high speeds, a streamlined shape, large tail, and nostrils that close are useful for diving, and specialized salt-secreting glands manage salt intake while at sea A Little History… A Little History… • Aristotle believed that species are fixed like rungs on a ladder, life going from simple to more complex. • With the study of fossils, things began to change… • Mid 1700’s, Georges Buffon suggested that the earth was very old Buffon • Fossils suggested that life forms change – Evolution was not a new theory by the early 1800’s, the question was, “what is the mechanism for evolution?” Lamarck Jean Baptiste Lamarck • suggested that the best explanation for fossils and the diversity of life is that organisms evolve. • presented one of the first theories to give evolution a mechanism: The Theory of Acquired Inheritance. • proposed that by using or not using its body parts, an individual tends to develop certain characteristics which it passes on to its offspring. – Ex. The giraffe’s long neck Charles Darwin • attended college initially to become a doctor but did not have the stomach for it • went to seminary at Cambridge. While there, he was intrigued by the biological and natural sciences • decided to take on the job of the ship’s naturalist on a ship that was to chart sections of South American coast line. • The HMS Beagle’s trip lasted five years! • While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed – similarities between living and fossil organisms – the diversity of life on the Galápagos Islands, such as blue-footed boobies, giant tortoises, and marine iguanas Figure 13.1A • The voyage of the Beagle Great Britain Europe North America Pacific Ocean Atlantic Ocean Africa Galápagos Islands Equator South America Australia Cape of Good Hope Tasmania Cape Horn Tierra del Fuego New Zealand Figure 13.1B Darwin gathers background information… • Darwin became convinced that the Earth was old and continually changing – While on the Beagle, Darwin read Scottish geologist Charles Lyell’s book entitled Principles of Geology which argued that the Earth had changed over time with life arising, changing and becoming extinct. – Darwin was also influenced by Thomas Malthus’ The Principles of Populations which stated that populations outgrow their food source and other resources creating competition. (Leads to famine, disease, homelessness, war, etc.) Evolution by means of natural selection. • Darwin spent 10 years studying his collection from the Beagle voyage. • Darwin noticed that many related species differed in the details and the details were designed for the region in which they were found. (ex. Finches, tortoises) • Darwin developed his theory that evolution occurs by natural selection. Natural Selection • the process by which individual organisms with favorable traits are more likely to survive and reproduce than those with unfavorable traits. • The genotypes associated with the favored traits will increase in frequency in the next generation. Given enough time, this passive process results in adaptations and speciation Natural Selection 1. Organisms have a tendency toward overproduction of offspring. (Think of how many eggs fish and insects lay!) 2. Individuals show variation in traits. 3. In the “struggle for existence,” favorable variations are more likely to survive and be passed on to offspring. 4. Gradually, offspring of survivors make up larger proportion of population, changing the population. Darwin’s Conclusions – living things also change, or evolve over generations – living species descended from earlier life-forms: descent with modification Charles Darwin British Naturalist 1809 -1882 “I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.” —Charles Darwin from "The Origin of Species" Darwin publishes his theory • The Origin of Species – “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” Another scientist comes to the same conclusion… Alfred Russel Wallace "...every species comes into existence coincident in time and space with a preexisting closely allied species." (1855) • In 1854 Wallace set out on a collecting expedition to the Malay Archipelago. During his travels he decided that the geographical distribution of species results from evolutionary forces. • Wallace deferred to Darwin and they corresponded for years. If there is such a thing as natural selection, is there such a thing as artificial selection? • Yes! Artificial selection is the breeding of certain traits over others. • Most examples of artificial selection fall into the category of selective breeding, in which particular individuals are selected for breeding because they possess desired characteristics or excluded from breeding because their traits are undesirable. Both processes have contributed to the domestication of animals and plants by humans. Evidence for Evolution • Fossil records • Homologous structures • Vestigial organs • Embryological development • Biochemical comparisons Comparative anatomy deals with the study of the structure of animal bodies. 1. The study of fossils provides strong evidence for evolution • Fossils and the fossil record strongly support the theory of evolution – Petrified trees Hominid skull Barosaurus Figure 13.2A, B – Ammonite casts – Fossilized organic matter in a leaf Figure 13.2C, D “Ice Man” Scorpion in amber Mammoth tusks Perch Figure 13.2E, F • The fossil record shows that organisms have appeared in a historical sequence • Many fossils link early extinct species with species living today – These fossilized hind leg bones link living whales with their land-dwelling ancestors Figure 13.2G, H 2. Homologous structures Body parts in different organisms that have similar bones and similar arrangements of muscles, blood vessels, and nerves and undergo similar embryological development, but do not necessarily serve the same function. Comparative anatomy Human Cat Whale Bat Figure 13.3A Homologous vs. Analogous Structures • Structures that evolve separately to perform a similar function are analogous. The wings of birds, bats, and insects, for example, have different embryological origins but are all designed for flight. 3. Vestigial Structures • Vestigial structures are anatomical structures of organisms in a species which are considered to have lost much or all of their original function through evolution. These structures are typically in a degenerate, atrophied, or rudimentary condition or form. Vestigial structures are often referred to as vestigial organs, though not all of them are actually organs. • Although the structures most commonly referred to as "vestigial" tend to be largely or entirely functionless, a vestigial structure need not necessarily be without use or function for the organism. Vestigial structures have lost their original main purpose, but they may retain lesser functionalities, or develop entirely new ones.[1] Thus, a "vestigial wing" need only be useless for flight to be vestigial; it may still serve some other purpose than that of a wing. Examples of Vestigial Structures 4. Embryological Development Embryology – the branch of biology that deals with the formation, early growth, and development of living organisms. Even before Darwin proposed the theory of evolution through natural selection, Ernst von Baer claimed that the more closely related any two species are, the more similar their development. 5. Biochemcial Comparisons (protein and DNA comparisons) Human Rhesus monkey Last common ancestor lived 26 million years ago (MYA), based on fossil evidence Mouse Chicken Frog Lamprey 80 MYA 275 MYA 330 MYA 450 MYA Figure 13.3B Chromosome Comparisons - Hominoid Chromosomes Why so similar? How can this happen? Inversion Meiosis - Tetrads Crossing Over Primate Cladogram Based on Chromosome changes VARIATION AND NATURAL SELECTION Variation is extensive in most populations • Phenotypic variation may be environmental or genetic in origin – But only genetic changes result in evolutionary adaptation – How do we get genetic variation? How natural selection affects variation • Natural selection tends to reduce variability in populations – The diploid condition preserves variation by “hiding” recessive alleles – Heterozygote advantage (think of sickle-cell disease). • Genetic load – the sum total of those alleles that yield some advantage when they are heterozygous but are lethal or deleterious when homozygous. – Some variations may be neutral, providing no apparent advantage or disadvantage – Example: human fingerprints Endangered species often have reduced variation • Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment – Studies have shown that cheetah populations exhibit extreme genetic uniformity – Thus they may have a reduced capacity to adapt to environmental challenges Figure 13.17 The perpetuation of genes defines evolutionary fitness • An individual’s Darwinian fitness is the contribution it makes to the gene pool (the entire collection of genes among a population) of the next generation relative to the contribution made by other individuals • Production of fertile offspring is the only score that counts in natural selection! • That is why the male lion will often kill the cubs when it takes over a new pride! The cubs do not reflect his genes! In other words, what adaptations make you more “appealing” to the opposite gender? • Sexual selection leads to the evolution of secondary sexual characteristics – These may give individuals an advantage in mating Figure 13.20A, B Frequency of individuals There are three general outcomes of natural selection Original population Phenotypes (fur color) Original population Evolved population Stabilizing selection Directional selection Diversifying selection Figure 13.19 Modes of Natural Selection • Stabilizing selection favors the middle – Ex. Birth weight • Directional selection favors one of the extremes, usually due to environment – Ex. Peppered moth • Diversifying selection favors the two extremes – Ex. Fish in a pond with very light sand and dark rocks regions. Natural Selection vs. Evolution • Natural selection involves the interaction of the environment and the individual. (Phenotype) – Natural selection eliminates the less fit, it does not produce new genotypes and phenotypes! • Evolution is a change in a population, not the individual! (Genotype) • In other words, populations evolve over many generations as the environment acts on/selects for the individuals! It is random! No thought process involved! Species and Speciation • Species - a population or group of populations whose members can interbreed and produce fertile offspring. (Which type of organism does not fit this definition?) • Speciation – the evolution of a new species? • But how? How can a new species evolve from an existing species? I’m glad you asked… The Role of Chance in Evolution Genetic drift- random changes in the allele frequency of a gene pool. Most likely to occur in small populations. Can lead to speciation- the formation of a new species. Changes (adaptations) become so severe that groups can no longer interbreed successfully. Maintaining separate species • Two different kinds of barriers can prevent closely related species from interbreeding 1. Prezygotic – prevents mating or fertilization – 5 types 2. Postzygotic – prevents reproduction of hybrids – 3 types Reproductive barriers keep species separate • Prezygotic and postzygotic reproductive barriers prevent individuals of different species from interbreeding Table 14.2 • Courtship ritual in blue-footed boobies is an example of one kind of prezygotic barrier, behavioral isolation • Many plant species have flower structures that are adapted to specific pollinators – This is an example of mechanical isolation, another prezygotic barrier Figure 14.2A, B • Hybrid sterility is one type of postzygotic barrier – A horse and a donkey may produce a hybrid offspring, a mule – Mules are sterile Figure 14.2C OK, so that is how a species is “maintained” but how do we change a species into a new species? Allopatric Speciation, a.k.a. Geographic Isolation Adaptive Radiation Sympatric Speciation It all comes down to stopping gene exchanges! MECHANISMS OF SPECIATION Geographic isolation can lead to speciation • When a population is cut off from its parent stock, species evolution may occur – An isolated population may become genetically unique as its gene pool is changed by natural selection, genetic drift, or mutation – This is called allopatric speciation Figure 14.3 Geographic isolation can occur in many ways… • By forming new islands, volcanoes can create opportunities for organisms (as well as remove opportunities causing extinctions!) – Example: Galápagos, Hawaii – Other examples: the formation of a mountain range, a shift in a river’s course, glaciers, etc. Figure 15.4B, C • Plate boundaries and earthquake activity can also create barriers (mountain ranges, valleys, sea level changes, etc.) Figure 15.3Ax Key adaptations may enable species to proliferate after extreme change. • Adaptations that have evolved in one environmental context may be able to perform new functions when conditions change – This is called exaptation. – Example: Plant species with catch basins, an adaptation to dry environments Figure 15.6 Islands are living laboratories of speciation • On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches Figure 14.4A Adaptive Radiation a.k.a. divergent evolution • The rapid (in geological terms!) emergence of new species from a common ancestor introduced to new and diverse environments. • Fills “new” ecological niches. • Leads to biodiversity! Cactus ground finch Medium ground finch Large ground finch Small Large cactus ground finch ground finch Small tree finch Vegetarian finch Medium tree finch Large tree finch Woodpecker finch Mangrove finch Green Gray warbler finch warbler finch Sharp-beaked ground finch Seed eaters Cactus flower eaters Ground finches Bud eaters Insect eaters Tree finches Warbler finches Common ancestor from South America mainland Figure 15.9 Biodiversity • The variety of organisms, their genetic information, and the biological communities in which they live. • Can be broken down into – Ecosystem diversity – variety of habitats, living communities, and ecological process in the living world. – Species diversity – the vast number of different organisms on Earth. – Genetic diversity – the sum total of all the different forms of genetic information carried by all living organisms and gives rise to inheritable variation. Convergent Evolution • Species not closely elated, independently evolve superficial similarities, because of the adaptations to a similar environment but do not have a common developmental origin . • Structures that are the result of convergent evolution are called analogous structures • Ex. The bat’s wing, bird’s wing, and a butterfly’s wing This can be seen at the biochemical level too! • Myosin – a protein found in muscle cells which reacts with other proteins causing the muscles to contract, causing movement. • Yeast have myosin too! Why? Allows for the movement of the organelles! • The original form of myosin made it possible for parts of the cells to move, the genes evolved into forms that help our bodies move. New species can also arise within the same geographic area as the parent species • In sympatric speciation, a new species may arise without geographic isolation – A failure in meiosis can produce diploid gametes – Self-fertilization can then produce a polyploid zygote (3n, 4n, 5n, etc.) – Most rapid form of speciation! Very common in plants. Parent species Zygote Meiotic error Selffertilization 2n = 6 Diploid Offspring may be viable and self-fertile 4n = 12 Tetraploid Unreduced diploid gametes Figure 14.5A Example: Polyploid plants clothe and feed us AA • Many plants are polyploid – They are the products of hybridization – The modern bread wheat is an example BB Wild Triticum (14 chromosomes) Triticum monococcum (14 chromosomes) AB Sterile hybrid (14 chromosomes) Meiotic error and self-fertilization AABB DD T. turgidum EMMER WHEAT (28 chromosomes) T. tauschii (wild) (14 chromosomes) ABD Sterile hybrid Meiotic error and self-fertilization AA BB DD T. aestivum BREAD WHEAT (42 chromosomes) Figure 14.6A 5 Potential Causes of Microevolution • Genetic Drift – Bottleneck effect – Founder effect • Gene Flow (ex. emigration, immigration, etc.) • Mutation • Non-random mating (ex. tall women tend to marry tall men, plants can’t move, island species, etc.) • Natural Selection or Differential Success Microevolution vs. Macroevolution • Microevolution is defined as the change of allele frequencies (that is, genetic variation due to processes such as selection, mutation, genetic drift, or even migration) within a population. • Macroevolution is defined as evolutionary change at the species level or higher, that is, the formation of new species, new genera, and so forth. Evolutionary 'fast-track' • Evolution has generally been thought of as a very gradual process • However, examples of rapid evolution have been observed – Antibiotic Resistance – HIV • Predator/Prey relationships can create the right pressures for rapid evolution! "We humans are part of complex ecosystems, and if we think we're above the effects of evolution, we're not looking close enough. If we want to understand epidemics and outbreaks of insects such as gypsy moths, we should not ignore the effect of evolution.” T. Yoshiba and R.O. Wayne, Cornell Univeristy The evolution of antibiotic resistance in bacteria is a serious public health concern (This is also an example of directional selection!) • The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria. This is also happening with fungicide and insecticide resistant organisms. – Such evolution only requires a point mutation! – Example: Mycobacterium tuberculosis • One example of rapid evolution occurred among mosquitoes who migrated into the London underground • In less than 150 years, Culex pipiens evolved into a new mosquito species, Culex molestus • The origin of new species is called speciation • The isolated mosquitoes adapted to their new underground environment – They altered their prey, mating habits, and breeding patterns • Environmental barriers that isolate populations are just one of many mechanisms in the evolution of species The tempo of speciation can appear steady or jumpy • According to the gradualist model of the origin of species – new species evolve by the gradual accumulation of changes brought about by natural selection • However, few gradual transitions are found in the fossil record Figure 14.8A • The punctuated equilibrium model suggests that speciation occurs in spurts – Rapid change occurs when an isolated population diverges from the ancestral stock – Virtually no change occurs for the rest of the species’ existence Figure 14.8B EARTH HISTORY AND MACROEVOLUTION The fossil record chronicles macroevolution • Macroevolution consists of the major changes in the history of life – The fossil record chronicles these changes, which have helped to devise the geologic time scale Figure 15.1 The actual ages of rocks and fossils mark geologic time • The sequence of fossils in rock strata indicates the relative ages of different species. This is called relative dating. • Radiometric (radioisotope) dating can gauge the actual ages of fossils. The isotopes act as a clock. To do this, you must ... – Know the ½ life of the isotope – Know how much isotope was originally present – Know how much of the isotope is left Example • 14C is the primary isotope used in dating – When an organism dies, no more C is added – ½ life of 14C is 5,770 years so all carbon is gone by 50,000. • This is a relatively short time compared to how old the Earth is. • Option: uranium 235 decays to lead 207, takes 713 million years! Problems using fossil records… • Have not found remains of “intermediate” or transition forms. – i.e. the missing Link! • Approx. 2/3 of all the organisms that ever lived were soft bodied! • Time averaging – trying to determine the length of time represented in a given fossil sample by taking into account the death, burial, and any movement of remains. – A bone among clam shells does not have to mean that they lived in the same time period or even in the same area! How do we keep up with all the different species? (Estimated to be 40 -100 million!) • Taxonomy (a.k.a. Systematic Biology) – The field of biology that determines the classification of an organism based on several features, such as structure, behavior, development, DNA, nutritional needs, and methods of obtaining food. – Based on evolutionary theory Why don’t woodpeckers get a headache? Adaptations for a woodpecking life style…