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
Hologenome theory of evolution wikipedia , lookup
The eclipse of Darwinism wikipedia , lookup
Punctuated equilibrium wikipedia , lookup
Organisms at high altitude wikipedia , lookup
Transitional fossil wikipedia , lookup
Evidence of common descent wikipedia , lookup
Evolutionary history of life wikipedia , lookup
Paleontology wikipedia , lookup
PowerLecture: Chapter 24 Principles of Evolution Learning Objectives Understand how variation occurs in populations and how changes in allele frequencies can be measured. Know how mutations, gene flow, genetic drift, and natural selection can influence the rate and direction of population change. Describe the types of selection mechanisms that help shape populations. Characterize the mechanisms of isolation that promote speciation. Learning Objectives (cont’d) Be able to cite what biologists generally accept as evidence to support concepts of evolution. Explain how observations from comparative morphology and comparative biochemistry are used to reconstruct the past. Describe how life might have spontaneously arisen on Earth approximately 3.5 billion years ago. Learning Objectives (cont’d) Understand the general physical features and behavioral patterns attributed to early primates. Know their relationship to other mammals. Trace primate evolutionary development. Understand the distinction between hominoid and hominid. Impacts/Issues Measuring Time Measuring Time How do we measure time? In geologic time we recognize that asteroids from the beginning of the universe are still orbiting the sun. About 65 million years ago one of these asteroids hit Earth, causing the extinction of the dinosaurs and other forms of life. Measuring Time Humanlike species were evolving in Africa about 5 million years ago. Modern humans have been around for about 100,000 years. Change could occur in the future, especially if the large asteroid predicted for 2028 happens to sweep a bit too close to Earth. Video: Asteroid Menace CLICK TO PLAY From ABC News, Biology in the Headlines, 2005 DVD. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu. A large asteroid impact could obliterate civilization and much of Earth’s biodiversity. Should we spend millions, even billions, of dollars to search for and track asteroids? a. Yes, even though the chance of impact is low, stakes are high. With warning, we can minimize damage. b. No, the likelihood of an impact is very low and the cost is high, so it is not worth it. Section 1 A Little Evolutionary History A Little Evolutionary History Evolution is defined by biologists as genetic change in a line of descent through successive generations. In the 1800s, the source of Earth’s amazing diversity of life forms was a matter of dispute. The prevailing belief in creation was being challenged by evidence supplied from new investigatory tools in the fields of geology and comparative anatomy. A Little Evolutionary History In 1831, botanist John Henslow arranged for a 22-year-old Charles Darwin to take ship as a naturalist aboard the HMS Beagle. Throughout the trip, Darwin studied and collected a variety of plants and animals. Darwin returned after five years at sea and with other scientists began pondering the growing evidence that life forms change over time. Figure 24.1 route of Beagle EQUATOR Galápagos Islands Fig 24.1a(1), p 444 Animation: The Galapagos Island CLICK TO PLAY Animation: Finches of the Galapagos CLICK TO PLAY A Little Evolutionary History Thomas Malthus had suggested that as a population outgrows its resources, its members must compete for what is available; some will not make it. Darwin’s observations found support for this idea in nature; chance could be part of the equation, but so was the variation of traits among members of the same species. Darwin’s work eventually led to the proposal of natural selection; decades later, genetics would provide understanding of how those traits could vary in the first place. Section 2 A Key Evolutionary Idea: Individuals Vary A Key Evolutionary Idea: Individuals Vary Evolution has two major components: Microevolution refers to the cumulative genetic changes that give rise to new species. Macroevolution applies to the large-scale patterns, trends, and rates of change among groups of species. A Key Evolutionary Idea: Individuals Vary Individuals don’t evolve—populations do. Evolution occurs only where there is change in the genetic makeup of a population. • • • A population is a group of individuals belonging to the same species, occupying the same given area. Members of a population demonstrate certain morphological, physiological, and behavioral traits in common. Populations exhibit immense variation among their individual members. Figure 24.2 A Key Evolutionary Idea: Individuals Vary Variation comes from genetic differences. All of the genes of a population make up the gene pool, but the genes have slightly different forms called alleles. Variations in traits in a population result when individuals inherit different combinations of alleles. Figure 24.3 Section 3 Microevolution: How New Species Arise Microevolution: How New Species Arise Mutation produces new forms of genes. Mutations are heritable changes in DNA and are the only source of new gene forms. • • Mutations are rare events. Whether they are harmful (lethal mutation), neutral, or beneficial depends on how the altered gene product performs under prevailing conditions. The majority of mutations are probably harmful, altering traits in such a way that an individual cannot survive or reproduce. Microevolution: How New Species Arise Natural selection can reshape the genetic makeup of a population. The theory of evolution by natural selection proposed by Darwin has several major points: • • • Individuals of a population vary in form, functioning, and behavior. Many variations can be passed from generation to generation. Some forms of a trait are more advantageous than others; they improve chances of surviving and reproducing. Microevolution: How New Species Arise • • • Natural selection is the difference in survival and reproduction that occurs among individuals differing in one or more traits. A population is evolving when some forms of a trait are increasing/decreasing, indicating changes in the commonality of the alleles. Over time, shifts in the makeup of the gene pools have generated Earth’s diverse life forms. Adaptation describes the tendency for organisms to come to have the characteristics that suit them best to the conditions of their environment. Microevolution: How New Species Arise Chance can also change a gene pool. Genetic drift is the random fluctuation in allele frequencies over time due to chance occurrences alone. • • It is more rapid in small populations. In the founder effect, a few individuals (carrying genes that may/may not be typical of the whole population) leave the original population to establish a new one. Animation: Simulation of Genetic Drift CLICK TO PLAY Microevolution: How New Species Arise In gene flow, genes move with the individuals when they move out of, or into, a population. • • The physical flow of alleles tends to minimize genetic variation between populations. It decreases the effects of mutation, genetic drift, and natural selection. The ability to interbreed defines a species. A species is one or more populations of individuals who can interbreed under natural conditions and produce fertile offspring. Microevolution: How New Species Arise Populations of one species are reproductively isolated from other populations. • • • Reproductive isolation is the stoppage of gene flow between two populations. In geographic isolation, barriers restrict gene flow between populations. Reproductive isolating mechanisms include isolation of gametes, structural isolation, isolation in time, unworkable hybrids, and behavioral isolation. Animation: Reproductive Isolating Mechanisms CLICK TO PLAY Microevolution: How New Species Arise Divergence is the process whereby local units of a population become reproductively isolated from other units and thus experience changes in gene frequencies between them, which may be enough to halt interbreeding and lead to speciation. Figure 24.4 time A time B time C time D daughter species daughter species parent species time Fig 24.4a, p.447 Microevolution: How New Species Arise Speciation can occur gradually or in “bursts.” According to the gradualism model, new species emerge through many small changes in form over long spans of time. In the punctuated equilibrium model, most evolutionary changes occur in bursts. Animation: Models of Speciation CLICK TO PLAY Animation: Directional Selection CLICK TO PLAY Section 4 Looking at Fossils and Biogeography Looking at Fossils and Biogeography A fossil is recognizable physical evidence of ancient life. Fossils are found in sedimentary rock. The most common fossils are bones, teeth, shells, seeds, and the other hard parts of different organisms. Figures 24.5 and 24.6 Looking at Fossils and Biogeography Fossilization begins with burial in sediments or volcanic ash. • • • Water invades, depositing ions and inorganic compounds. Pressure from accumulating sediments transforms the trapped material into stony fossils. Organisms are most likely to be preserved when they are buried rapidly and in the absence of oxygen. Stratification is the layering of sedimentary deposits formed over long geologic time. Looking at Fossils and Biogeography Completeness of the fossil record varies. The fossil record is incomplete: large-scale movements in the Earth’s crust have obliterated evidence from crucial periods, and soft-bodied organisms decayed rather than fossilized. • • Population densities and body size further skew the record. The fossil record is also heavily biased toward certain environments. Radiometric dating tracks the radioactive decay of isotopes trapped in sediments to allow scientists to date the fossils they do find. Animation: Radioisotope Decay CLICK TO PLAY Animation: Radiometric Dating CLICK TO PLAY Looking at Fossils and Biogeography Biogeography provides other clues. Biogeography addresses the question of why certain species occur where they do on the surface of the earth. • • The simplest explanation is that they evolved there from ancestral species. Alternatively, they may have dispersed there from someplace else. The study of plate tectonics reveals that the continents once formed a giant supercontinent called Pangea, thus shedding light on the possible dispersal routes for different species. EURASIAN PLATE NORTH AMERICAN PACIFIC PLATE PLATE COCOS PLATE NAZCA PLATE PACIFIC PLATE SOUTH AMERICAN PLATE SOMALI PLATE AFRICAN PLATE PHILLIPINE PLATE INDOAUSTRALIAN PLATE ANTARCTIC PLATE © 2007 Thomson Higher Education Fig 24.7a, p.449 Animation: Plate Tectonics CLICK TO PLAY 420 mya 260 mya 65 mya 10 mya Fig 24.7b, p.449 Animation: Geological Time Scale CLICK TO PLAY Section 5 Comparing the Form and Development of Body Parts Comparing the Form and Development of Body Parts Comparing body forms may reveal evolutionary connections. Through comparative morphology, researchers reconstruct evolutionary history on the basis of information contained in the observed patterns of body form. • • Homologous structures are the same body features that have become modified in different lines of descent from common ancestors (morphological divergence). One example of this would be the bones in the forelimbs of vertebrates. 4 3 a. early reptile 21 5 21 3 4 b. pterosaur 1 c. chicken 2 3 1 2 d. bat 3 4 1 5 e. porpoise 2 4 3 5 f. penguin 2 1 3 4 2 3 g. human 5 Fig 24.8, p.450 Comparing the Form and Development of Body Parts Analogous structures are used for similar functions in similar environments by dissimilar and distantly related species. Morphological convergence is the adoption of similar form and function over periods of time (example: the distinctive torsos of dolphins and tuna). Animation: Morphological Divergence CLICK TO PLAY Comparing the Form and Development of Body Parts Development patterns also provide clues. Different organisms may show similarities in morphology during their embryonic stages; these similarities often indicate evolutionary relationships. • • Some of the variation seen in adult vertebrates is due to mutations in regulatory genes that control the rates of growth of different body parts. One example can be seen in chimpanzees and humans; as infants skull structure is virtually identical, but adults have very different appearances. fish reptile bird (chicken) mammal (human) Fig 24.9a, p 451 fish reptile bird (chicken) mammal (human) Stepped Art Fig 24.9a, p 451 adult shark © 2007 Thomson Higher Education human embryo (three millimeters long) Fig 24.9b, p 451 Animation: Comparative Embryos CLICK TO PLAY infant adult a. Chimpanzee skull infant adult b. Human skull Fig 24.10, p 451 Animation: Morphing Skulls CLICK TO PLAY Comparing the Form and Development of Body Parts Vestigial structures are apparently useless structures that are left over from a time when more functional versions were important for an ancestor. backbone (vertebral column) pelvic girdle (hind legs attach to these) coccyx (bones where many other mammals have a tail) small bone attached to pelvic girdle thighbone attached to pelvic girdle Fig. 24.11, p.451 Animation: Comparative Pelvic Anatomy CLICK TO PLAY Section 6 Comparing Biochemistry Comparing Biochemistry Genes and gene products (proteins) of different species contain information about evolutionary relationships. By comparing body form, for example, all primates appear to be related; this can be confirmed or denied based on analysis of the amino acid sequences in proteins. Figure 24.15a-b Comparing Biochemistry The degree of similarity of amino acid sequences is a measure of species relatedness; fewer differences indicate a closer relationship and vice versa. Cytochrome c is an example of a protein that has changed very little over time; in humans and chimps, the sequence is identical, but there are 19 amino acid differences between humans and turtles. Comparing Biochemistry Nucleotide sequences can also be analyzed for neutral mutations, which provide information on variation over time; calculations of neutral mutations can give an indication of “when” species divergence occurred—a molecular clock. Section 7 How Species Come and Go How Species Come and Go Extinction is the irrevocable loss of a species. Background extinction is the steady rate of species disappearance over time as local conditions change. Mass extinction is the disappearance of major groups of species on a global scale due to catastrophic events. Human activities have led to an increase in the extinction rate in the past few centuries. How Species Come and Go In adaptive radiation, new species arise. In adaptive radiation, new species move into new habitats during bursts of microevolution. • • Many adaptive radiations have occurred in the first few million years following major mass extinction events. Mammals, for example, arose and radiated into the habitats vacated by extinction of the dinosaurs. Adaptive radiations have also occurred in humans; Homo erectus radiated away from Homo habilis some 2 million years ago and eventually gave rise to Homo sapiens about 100,000 years ago. 1.8 meters (6 feet) thighbone (femur) shinbone (tibia) Neandertal Modern Inuit Homo erectus Modern Masai Fig 24.12., p.452 Animation: Genetic Distance Between Human Groups CLICK TO PLAY 0.2% 0.1% 0% = genetic distance New Guinea, Australia Pacific Islands Southeast Asia Arctic, Northeast Asia North, South America Northeast Asia Europe, Middle East Africa Proposed Family Tree for Homo Sapiens Fig 24.13, p.453 Artificial Selection Figures 24.25 and 24.26 Section 8 Endangered Species Endangered Species Human activities are driving many species to extinction. An endangered species is an endemic species that is very vulnerable to extinction; endemic species are those found only in one region of the world and nowhere else. Figure 24.14 Endangered Species Habitat loss is the major threat to more than 90% of the endangered species. Introduction of exotic species is also displacing endemic species. Human trade in animals and animal parts also claims a large toll. Figure 24.24 Section 9 Evolution from a Human Perspective Evolution from a Human Perspective All forms of life can be classified and grouped for greater ease in understanding their evolutionary relationships. The binomial system of nomenclature used two names—genus and species—to identify each distinct organism. Modern systems use several groupings to organize the genera (from the broadest grouping down to the most specific grouping): domain, kingdom, phylum, class, order, family, genus, and species. Classification of Humans Evolution from a Human Perspective Five trends mark human evolution. Precision grip and power grip. • • • Prehensile movements allowed fingers to wrap around objects in a grasp. Opposable thumb and fingers allowed more refined use of the hand. The precision grip and power grip movements of the human hand allowed for tool making. Evolution from a Human Perspective Improved daytime vision: resulted from forward directed eyes (depth perception) with their increased ability to discern shape, movement, color, and light intensity. Changes in dentition: resulted in humans having smaller teeth of more uniform length; generally the jaws and teeth became less specialized. Jaw shape and teeth of an early primate Evolution from a Human Perspective Changes in the brain and behavior. • • The brain increased in size and complexity, resulting in new behaviors. Culture evolved; culture is composed of all the behavior patterns that are passed between generations by learning and symbolic behavior, especially language. human chimp gibbon macaque lemur 70 60 postreproductive years 50 40 adult 30 20 10 subadult infancy 18 24 30 34 38 time in uterus (weeks) Fig 24.16, p.455 Evolution from a Human Perspective Upright walking. • • Bipedalism is the habitual two-legged gait characteristic of humans. Compared with monkeys and apes, humans have a shorter, S-shaped, somewhat flexible backbone, which works with shoulder blades and pelvic girdle to allow for upright movement. Figure 24.17 foramen magnum Fig 24.17b, p 455 foramen magnum Fig 24.17c, p 455 Animation: Primate Skeletons CLICK TO PLAY Section 10 Emergence of Early Humans Emergence of Early Humans Apelike forms, the hominoids, spread through Africa, Asia, and Europe between 23 and 5 million years ago. At this time, the earth began to change and most of the hominoids went extinct. One survivor was the common ancestor of both the great apes and the first hominids. Figure 24.18b-c Emergence of Early Humans Early hominids lived in Central Africa. Sahelanthropus tchadensis was one of the first species to evolve in Central Africa about 6 to 7 million years ago, during the time when the ancestors of humans were becoming distinct from the apes. Australopithecus afarensis is one of the species that walked upright across the African plain some 3.7 million years ago. Animation: Fossils of Australopiths CLICK TO PLAY Emergence of Early Humans Is Homo sapiens “out of Africa”? Species of humans appeared a little over 2 million years ago in eastern Africa; the earliest humans were Homo habilis and Homo rudolfensis. • • They had increased brain size, a smaller face, and thickly enameled teeth, which permitted a wider variety of diet. They also used tools. H. habilis 1.9–1.6 million years Fig 24.18d, p 456 Homo rudolfensis 2.4–1.8 million years Fig 24.18e, p 456 Emergence of Early Humans Divergence produced Homo erectus; these early humans began migrating out of Africa into Europe and Asia in waves. • • Homo erectus still lived in Southeast Asia between 53,000 and 37,000 years ago. Neanderthals lived as recently as 30,000 years ago in Europe and the Near East, and their extinction coincided with the origin of modern humans between 40,000 and 30,000 years ago. Emergence of Early Humans Where did Homo sapiens originate? Two models are used to interpret the evidence provided by measurements of small genetic differences seen among humans today: • • The multiregional model proposes that Homo sapiens evolved from Homo erectus in the various parts of the world to which it migrated many years before; gene flow prevented speciation. In the African emergence model, Homo sapiens originated in Africa and migrated out to replace the Homo erectus populations already there; various lines of evidence support this model. H. sapiens fossil from Ethiopia, 160,000 years old Fig 24.20b, p 457 40,000 years ago 15,000-30,000 years ago 60,000 years ago 160,000 years ago 35,000-60,000 years ago Fig 24.20a, p.457 Animation: Primate Evolutionary Tree CLICK TO PLAY Section 11 Earth’s History and the Origin of Life Earth’s History and the Origin of Life Primordial Earth was a hard place 4 billion years ago, but within 200 million years life had appeared on its surface. Figure 24.21 Earth’s History and the Origin of Life Conditions on early Earth were intense. The early atmosphere was likely composed of gaseous hydrogen, nitrogen, carbon monoxide, and carbon dioxide; there likely was no oxygen or water. Cooling and solidification of the Earth’s crust allowed water to condense and rain to fall, creating early seas. Organic materials and water were necessary for the beginnings of life. Earth’s History and the Origin of Life Biological molecules paved the way for cells to evolve. The first living cells probably emerged around 3.8 billion years ago and resembled modern anaerobic bacteria. Prior to this first cell, however, chemical evolution would have had to occur. Figure 24.22a membrane-bound proto-cells living cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNA RNA formation of protein-RNA systems, evolution of DNA enzymes and other proteins formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Fig 24.23a, p.459 membrane-bound proto-cells living cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNA RNA formation of protein-RNA systems, evolution of DNA enzymes and other proteins formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Stepped Art Fig 24.23a, p.459 Earth’s History and the Origin of Life Experiments give us ideas about how life first arose on Earth. Simulations of the conditions on early Earth show how molecules such as amino acids, glucose, ribose, deoxyribose, and other sugars could have been produced. How did complex compounds such as proteins form? • • One scenario of chemical synthesis proposes that clay templates served as “enzymes” to favor bond formation among chemicals. Alternatively, complex compounds may have first formed near deep-sea hydrothermal vents. Earth’s History and the Origin of Life Enzymes, ATP, and other molecules could have assembled spontaneously in places where they were in close physical proximity, which would have promoted chemical interactions—the beginnings of metabolic pathways. From accumulated organic compounds emerged replicating systems consisting of DNA, RNA, proteins, and enzymes. Perhaps RNA strands were capable of enzyme activity (as has recently been demonstrated) and promoted protein synthesis. The first cells were probably membrane-bound sacs containing nucleic acids that served as templates for proteins. Animation: Miller’s Reaction Chamber Experiment CLICK TO PLAY Animation: Milestones in the History of Life CLICK TO PLAY