Chapter 22

1. Chapter 22 Descent with Modification: A Darwinian View of Life

2. Overview: Darwin Introduces a Revolutionary Theory • A new era of biology began on November 24, 1859 • The day Charles Darwin published On the Origin of Species by Means of Natural Selection

3. Figure 22.1 • The Origin of Species • Focused biologists’ attention on the great diversity of organisms

4. Darwin made two major points in his book • He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral species • He proposed a mechanism for the evolutionary process - natural selection

5. Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species • In order to understand why Darwin’s ideas were revolutionary • We need to examine his views in the context of other Western ideas about Earth and its life

6. Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, nutural selection) Mendel (inheritance) Wallace (evolution, natural selection) American Revolution French Revolution U.S. Civil War 1800 1850 1900 1750 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his theory of evolution. Lyell publishes Principles of Geology. 1830 Darwin travels around the world on HMS Beagle. 1831–1836 1837 Darwin begins his notebooks on the origin of species. 1844 Darwin writes his essay on the origin of species. 1858 Wallace sends his theory to Darwin. TheOrigin of Species is published. 1859 1865 Mendel publishes inheritance papers. Figure 22.2 • The historical context of Darwin’s life and ideas

7. The Scale of Nature and Classification of Species • The Greek philosopher Aristotle • Viewed species as fixed and unchanging • The Old Testament of the Bible • Holds that species were individually designed by God and therefore perfect

8. Carolus Linnaeus • Interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Was a founder of taxonomy, classifying life’s diversity “for the greater glory of God”

9. Figure 22.3 Fossils, Cuvier, and Catastrophism • The study of fossils • Helped to lay the groundwork for Darwin’s ideas • Fossils are remains or traces of organisms from the past • Usually found in sedimentary rock, which appears in layers or strata

10. Paleontology, the study of fossils • Was largely developed by French scientist Georges Cuvier • Cuvier opposed the idea of gradual evolutionary change • And instead advocated catastrophism, speculating that each boundary between strata represents a catastrophe • What are strata?

11. Theories of Gradualism • Gradualism • Is the idea that profound change can take place through the cumulative effect of slow but continuous processes

12. Geologists Hutton and Lyell • Perceived that changes in Earth’s surface can result from slow continuous actions still operating today • Uniformitarianism • Exerted a strong influence on Darwin’s thinking

13. Figure 22.4 Lamarck’s Theory of Evolution • Lamarck hypothesized that species evolve • Through use and disuse and the inheritance of acquired traits • But the mechanisms he proposed are unsupported by evidence

14. Concept 22.2: In The Origin of Species, Darwin proposed that species change through natural selection • As the 19th century dawned • It was generally believed that species had remained unchanged since their creation, but a major change would challenge this thinking

15. The Voyage of the Beagle • During his travels on the Beagle • Darwin observed and collected many specimens of South American plants and animals • Darwin observed various adaptations of plants and animals • That inhabited many diverse environments

16. England EUROPE NORTH AMERICA ATLANTIC OCEAN PACIFIC OCEAN Galápagos Islands HMS Beagle in port AFRICA SOUTH AMERICA Darwin in 1840, after his return AUSTRALIA Cape of Good Hope Andes Tasmania Cape Horn New Zealand Tierra del Fuego Figure 22.5 • Darwin’s interest in the geographic distribution of species • Was kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South America

17. Darwin’s Focus on Adaptation • As Darwin reassessed all that he had observed during the voyage of the Beagle • He began to perceive adaptation to the environment and the origin of new species as closely related processes

18. (a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp. (c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground. Figure 22.6a–c (b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects. • From studies made years after Darwin’s voyage • Biologists have concluded that this is indeed what happened to the Galápagos finches

19. In 1844, Darwin wrote a long essay on the origin of species and natural selection • But he was reluctant to introduce his theory publicly, anticipating the uproar it would cause • In June 1858 Darwin received a manuscript from Alfred Russell Wallace • Who had developed a theory of natural selection similar to Darwin’s • Darwin quickly finished The Origin of Species • And published it the next year

20. The Origin of Species • Darwin developed two main ideas • Evolution explains life’s unity and diversity • Natural selection is a cause of adaptive evolution

21. Descent with Modification • The phrase descent with modification • Summarized Darwin’s perception of the unity of life • States that all organisms are related through descent from an ancestor that lived in the remote past

22. Sirenia (Manatees and relatives) Loxodonta africana (Africa) Elephas maximus (Asia) Loxodonta cyclotis (Africa) Hyracoidea (Hyraxes) Years ago Stegodon Mammut Mammuthus Deinotherium Platybelodon Millions of years ago Barytherium Moeritherium Figure 22.7 • In the Darwinian view, the history of life is like a tree • With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms

23. Natural Selection and Adaptation • Evolutionary biologist Ernst Mayr • Has dissected the logic of Darwin’s theory into three inferences based on five observations

24. Figure 22.8 • Observation #1: For any species, population sizes would increase exponentially • If all individuals that are born reproduced successfully

25. Observation #2: Nonetheless, populations tend to be stable in size • Except for seasonal fluctuations • Observation #3: Resources are limited • Inference #1: Production of more individuals than the environment can support • Leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

26. Figure 22.9 • Observation #4: Members of a population vary extensively in their characteristics • No two individuals are exactly alike

27. Observation #5: Much of this variation is heritable • Inference #2: Survival depends in part on inherited traits • Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

28. Inference #3: This unequal ability of individuals to survive and reproduce • Will lead to a gradual change in a population, with favorable characteristics accumulating over generations

29. Lateral buds Terminal bud Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Kale Flower and stems Stem Broccoli Kohlrabi Wild mustard Figure 22.10 Artificial Selection • In the process of artificial selection • Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits

30. Summary of Natural Selection • Natural selection is differential success in reproduction • That results from the interaction between individuals that vary in heritable traits and their environment

31. (a) A flower mantidin Malaysia (b) A stick mantidin Africa Figure 22.11 • Natural selection can produce an increase over time • In the adaptation of organisms to their environment • If an environment changes over time • Natural selection may result in adaptation to these new conditions

32. Concept 22.3: Darwin’s theory explains a wide range of observations • Darwin’s theory of evolution • Continues to be tested by how effectively it can account for additional observations and experimental outcomes

33. Natural Selection in Action • Two examples • Provide evidence for natural selection

34. Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools and measured the average age and size of guppies at maturity over an 11-year period (30 to 60 generations). EXPERIMENT Pools with killifish, but not guppies prior to transplant Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Guppies: Larger at sexual maturity than those in “pike-cichlid pools” Predator: Pike-cichlid; preys mainly on large guppies Guppies: Smaller at sexual maturity than those in “killifish pools” Figure 22.12 Differential Predation in Guppy Populations • Researchers have observed natural selection • Leading to adaptive evolution in guppy populations

35. RESULTS After 11 years, the average size and age at maturity of guppies in the transplanted populations increased compared to those of guppies in control populations. Control Population: Guppies from pools with pike-cichlids as predators 185.6 92.3 85.7 161.5 Weight of guppies at maturity (mg) Age of guppies at maturity (days) 58.2 48.5 76.1 67.5 Experimental Population: Guppies transplanted to pools with killifish as predators Males Females Males Females CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered selection pressure resulted in an observable evolutionary change in the experimental population.

36. The Evolution of Drug-Resistant HIV • In humans, the use of drugs • Selects for pathogens that through chance mutations are resistant to the drugs’ effects • Natural selection is a cause of adaptive evolution • The ability of bacteria and viruses to evolve rapidly • Poses a challenge to our society

37. Researchers have developed numerous drugs to combat HIV • But using these medications selects for viruses resistant to the drugs Patient No. 1 Patient No. 2 Percent of HIV resistant to 3TC Patient No. 3 Weeks Figure 22.13

38. Homology, Biogeography, and the Fossil Record • Evolutionary theory • Provides a cohesive explanation for many kinds of observations

39. Homology • Homology • Is similarity resulting from common ancestry

40. Human Cat Bat Whale Figure 22.14 Anatomical Homologies • Homologous structures between organisms • Are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor

41. Pharyngeal pouches Post-anal tail Chick embryo Human embryo Figure 22.15 • Comparative embryology • Reveals additional anatomical homologies not visible in adult organisms

42. Vestigial organs • Are some of the most intriguing homologous structures • Are remnants of structures that served important functions in the organism’s ancestors • Examples?

43. Molecular Homologies • Biologists also observe homologies among organisms at the molecular level • Such as genes that are shared among organisms inherited from a common ancestor

44. Homologies and the Tree of Life • The Darwinian concept of an evolutionary tree of life • Can explain the homologies that researchers have observed

45. Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Species 100% Human Rhesus monkey 95% Mouse 87% Chicken 69% Frog 54% 14% Figure 22.16 Lamprey • Anatomical resemblances among species • Are generally reflected in their molecules, their genes, and their gene products

46. Biogeography • Darwin’s observations of the geographic distribution of species, biogeography • Formed an important part of his theory of evolution

47. NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Figure 22.17 • Some similar mammals that have adapted to similar environments • Have evolved independently from different ancestors

48. The Fossil Record • The succession of forms observed in the fossil record • Is consistent with other inferences about the major branches of descent in the tree of life

49. Figure 22.18 • The Darwinian view of life • Predicts that evolutionary transitions should leave signs in the fossil record • Paleontologists • Have discovered fossils of many such transitional forms

50. What Is Theoretical about the Darwinian View of Life? • In science, a theory • Accounts for many observations and data and attempts to explain and integrate a great variety of phenomena