CHAPTER 13 How Populations Evolve

1. CHAPTER 13How Populations Evolve SSHS AP Biology

2. Clown, Fool, or Simply Well Adapted? • All organisms have evolutionary adaptations • Inherited characteristics that enhance their ability to survive and reproduce • The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment • Large, webbed feet help propel the bird throughwater at high speeds

3. Specialized salt-secreting glands manage salt intake while at sea • A streamlined shape, large tail, and nostrils that close are useful for diving

4. EVIDENCE OF EVOLUTION 13.1 A sea voyage helped Darwin frame his theory of evolution • Aristotle and the Judeo-Christian culture believed that species are fixed • Fossils suggested that life forms change • This idea was embraced by Lamarck in the early 1800s

5. similarities between living and fossil organisms • the diversity of life on the Galápagos Islands, such as blue-footed boobies and giant tortoises • While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed Figure 13.1A

6. The voyage of the Beagle Great Britain Europe NorthAmerica PacificOcean AtlanticOcean Africa GalápagosIslands Equator SouthAmerica Australia Andes Cape ofGood Hope Tasmania Cape Horn NewZealand Tierra del Fuego Figure 13.1B

7. He concluded that living things also change, or evolve over generations • He also stated that living species descended from earlier life-forms: descent with modification • Darwin became convinced that the Earth was old and continually changing

8. 13.2 The study of fossils provides strong evidence for evolution • Fossils and the fossil record strongly support the theory of evolution • Hominid skull • Petrified trees Figure 13.2A, B

9. Ammonite casts • Fossilized organic matter in a leaf Figure 13.2C, D

10. Scorpion in amber • “Ice Man” Figure 13.2E, F

11. 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

12. 13.3 A mass of evidence validates the evolutionary view of life • Other evidence for evolution comes from • Biogeography • Comparative anatomy • Comparative embryology Human Cat Whale Bat Figure 13.3A

13. Molecular biology Human Rhesus monkey Mouse Chicken Frog Lamprey Last commonancestor lived26 million yearsago (MYA),based onfossil evidence 80 MYA 275 MYA 330 MYA 450 MYA Figure 13.3B

14. DARWIN’S THEORY AND THE MODERN SYNTHESIS 13.4 Darwin proposed natural selection as the mechanism of evolution • Darwin observed that • organisms produce more offspring than the environment can support • organisms vary in many characteristics • these variations can be inherited

15. Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted • Darwin saw natural selection as the basic mechanism of evolution • As a result, the proportion of individuals with favorable characteristics increases • Populations gradually change in response to the environment

16. Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment • This is called artificial selection • Example of artificial selection in plants: five vegetables derived from wild mustard Figure 13.4A

17. Example of artificial selection in animals: dog breeding English springerspaniel German shepherd Yorkshire terrier Mini-dachshund Golden retriever Hundreds tothousands of yearsof breeding(artificial selection) Ancestral dog Figure 13.4B

18. These five canine species evolved from a common ancestor through natural selection African wilddog Coyote Fox Wolf Jackal Thousands tomillions of yearsof natural selection Ancestral canine Figure 13.4C

19. 13.5 Connection: Scientists can observe natural selection in action • Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms • Example: camouflage adaptations of mantids that live in different environments Figure 13.5A

20. The evolution of insecticide resistance is an example of natural selection in action Insecticideapplication Chromosome with geneconferring resistanceto insecticide Additionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill grow Survivor Figure 13.5B

21. 13.6 Populations are the units of evolution • A species is a group of populations whose individuals can interbreed and produce fertile offspring • Human populations tend to concentrate locally, as this satellite photograph of North America shows • The modern synthesis connects Darwin’s theory of natural selection with population genetics Figure 13.6

22. 13.7 Microevolution is change in a population’s gene pool over time • A gene pool is the total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool

23. 13.8 The gene pool of a nonevolving population remains constant over the generations • Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool • To test this, let’s look at an imaginary, nonevolving population of blue-footed boobies Webbing No webbing Figure 13.8A

24. Phenotypes • We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Genotypes WW Ww ww Number of animals(total = 500) 320 160 20 Genotype frequencies 320/500 = 0.64 160/500 = 0.32 20/500 = 0.04 Number of allelesin gene pool(total = 1,000) 640 W 160 W + 160 w 40 w Allele frequencies 800/1,000 = 0.8 W 200/1,000 = 0.2 w Figure 13.8B

25. Recombinationof alleles fromparent generation W sperm p = 0.8 W egg p = 0.8 SPERM EGGS WW p2 = 0.64 w sperm q = 0.2 w egg q = 0.2 WW qp = 0.16 Ww pq = 0.16 ww q2 = 0.04 Next generation: Genotype frequencies 0.64 WW 0.32 Ww 0.04 ww Allele frequencies 0.8 W 0.2 w Figure 13.8C

26. 13.9 Connection: The Hardy-Weinberg equation is useful in public health science • Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population • Example: phenylketonuria (PKU)

27. 13.10 Five conditions are required for Hardy-Weinberg equilibrium • The population is very large • The population is isolated • Mutations do not alter the gene pool • Mating is random • All individuals are equal in reproductive success

28. 13.11 There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance • Genetic drift can cause the bottleneck effect Originalpopulation Bottleneckingevent Survivingpopulation Figure 13.11A

29. or the founder effect Figure 13.11B, C

30. Mutation changes alleles • Natural selection leads to differential reproductive success • Gene flow can change a gene pool due to the movement of genes into or out of a population

31. 13.12 Adaptive change results when natural selection upsets genetic equilibrium • Natural selection results in the accumulation of traits that adapt a population to its environment • If the environment should change, natural selection would favor traits adapted to the new conditions

32. VARIATION AND NATURAL SELECTION 13.13 Variation is extensive in most populations • Phenotypic variation may be environmental or genetic in origin • But only genetic changes result in evolutionary adaptation

33. Many populations exhibit polymorphism and geographic variation Figure 13.13

34. 13.14 Connection: Mutation and sexual recombination generate variation Parents A1 A1 A2 A3 MEIOSIS A1 A2 A3 Gametes FERTILIZATION Offspring,with newcombinationsof alleles A1 A2 A1 A3 and Figure 13.14

35. 13.15 Overview: How natural selection affects variation • Natural selection tends to reduce variability in populations • The diploid condition preserves variation by “hiding” recessive alleles • Balanced polymorphism may result from the heterozygote advantage

36. 13.16 Not all genetic variation may be subject to natural selection • Some variations may be neutral, providing no apparent advantage or disadvantage • Example: human fingerprints Figure 13.16

37. 13.17 Connection: 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

38. 13.18 The perpetuation of genes defines evolutionary fitness • An individual’s Darwinian fitness is the contribution it makes to the gene pool 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

39. 13.19 There are three general outcomes of natural selection Originalpopulation Frequency ofindividuals Phenotypes (fur color) Originalpopulation Evolvedpopulation Stabilizing selection Directional selection Diversifying selection Figure 13.19

40. 13.20 Sexual selection may produce sexual dimorphism • Sexual selection leads to the evolution of secondary sexual characteristics • These may give individuals an advantage in mating Figure 13.20A, B

41. 13.21 Natural selection cannot fashion perfect organisms • This is due to: • historical constraints • adaptive compromises • chance events • availability of variations

42. 13.22 Connection: The evolution of antibiotic resistance in bacteria is a serious public health concern • The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria • Example: Mycobacterium tuberculosis Figure 13.22