PowerLecture: Chapter 24

1. PowerLecture:Chapter 24 Principles of Evolution

2. 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.

3. 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.

4. 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.

5. Impacts/Issues Measuring Time

6. 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.

7. 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.

8. 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.

9. Section 1 A Little Evolutionary History

10. 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.

11. 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

12. Fig 24.1a(1), p 444 route of Beagle EQUATOR Galápagos Islands

13. 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.

14. Section 2 A Key Evolutionary Idea: Individuals Vary

15. 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.

16. 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

17. 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

18. Section 3 Microevolution: How New Species Arise

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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

26. Fig 24.4a, p.447 time A time B time C time D daughter species daughter species parent species time

27. 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.

28. Section 4 Looking at Fossils and Biogeography

29. 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

30. 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.

31. 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.

32. 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.

33. Fig 24.7a, p.449 © 2007 Thomson Higher Education EURASIAN PLATE NORTH AMERICAN PLATE PACIFIC PLATE PACIFIC PLATE PHILLIPINE PLATE COCOS PLATE SOUTH AMERICAN PLATE SOMALI PLATE NAZCA PLATE INDO- AUSTRALIAN PLATE AFRICAN PLATE ANTARCTIC PLATE

34. Fig 24.7b, p.449 420 mya 260 mya 65 mya 10 mya

35. Section 5 Comparing the Form and Development of Body Parts

36. 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.

37. Fig 24.8, p.450 1 a. early reptile 2 3 4 5 1 2 3 b. pterosaur 4 1 c. chicken 2 3 1 2 d. bat 1 3 4 5 e. porpoise 2 4 5 3 f. penguin 2 3 1 2 g. human 3 4 5

38. 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).

39. 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.

40. Fig 24.9a, p 451 fish reptile bird (chicken) mammal (human)

41. Fig 24.9a, p 451 fish reptile bird (chicken) mammal (human) Stepped Art

42. Fig 24.9b, p 451 human embryo (three millimeters long) adult shark © 2007 Thomson Higher Education

43. Fig 24.10, p 451 infant adult a. Chimpanzee skull infant adult b. Human skull

44. 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.

45. Fig. 24.11, p.451 backbone (vertebral column) pelvic girdle (hind legs attach to these) coccyx (bones where many other mammals have a tail) thighbone attached to pelvic girdle small bone attached to pelvic girdle

46. Section 6 Comparing Biochemistry

47. 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

48. 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.

49. 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.

50. Section 7 How Species Come and Go