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Chapter 22

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Chapter 22

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  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 • The Origin of Species focused biologists’ attention on the great diversity of organisms Video: Galápagos Marine Iguana

  3. Darwin made two major points in his book: • Many current species are descendants of ancestral species • Natural selection is a mechanism for this evolutionary process

  4. Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species • To understand why Darwin’s ideas were revolutionary, we must examine them in relation to other Western ideas about Earth and its life

  5. LE 22-2 Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Mendel (inheritance) Wallace (evolution, natural selection) American Revolution U.S. Civil War French Revolution 1850 1900 1750 1800 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his theory of evolution. 1830 Lyell publishes Principles of Geology. 1831–1936 Darwin travels around the world on HMS Beagle. 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. 1859 The Origin of Species is published. Mendel publishes inheritance papers. 1865

  6. Resistance to the Idea of Evolution • The Origin of Species • Shook the deepest roots of Western culture • Challenged a worldview that had been prevalent for centuries

  7. The Scale of Nature and Classification of Species • The Greek philosopher Aristotle viewed species as fixed and unchanging • The Old Testament holds that species were individually designed by God and therefore perfect • Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose • Linnaeus was a founder of taxonomy, the branch of biology concerned with classifying organisms

  8. 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 Video: Grand Canyon

  9. Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier • Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe

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

  11. Geologists Hutton and Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today • This view strongly influenced Darwin’s thinking

  12. Lamarck’s Theory of Evolution • Lamarck hypothesized that species evolve through use and disuse and the inheritance of acquired traits • The mechanisms he proposed are unsupported by evidence

  13. 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 • However, a few doubts about the permanence of species were beginning to arise

  14. Darwin’s Research • As a boy and into adulthood, Charles Darwin had a consuming interest in nature • After receiving his B.A. degree, he was accepted on board the HMS Beagle, which was embarking on a voyage around the world

  15. The Voyage of the Beagle • During his travels on the Beagle, Darwin collected specimens of South American plants and animals • He observed adaptations of plants and animals that inhabited many diverse environments • His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America

  16. LE 22-5 England EUROPE NORTH AMERICA PACIFIC OCEAN ATLANTIC OCEAN AFRICA Galápagos Islands HMS Beagle in port Equator SOUTH AMERICA Darwin in 1840, after his return AUSTRALIA Cape of Good Hope Andes Tasmania Cape Horn New Zealand Tierra del Fuego

  17. Video: Albatross Courtship Ritual Video: Blue-footed Boobies Courtship Ritual Video: Galápagos Island Overview Video: Galápagos Sea Lion Video: Soaring Hawk Video: Galápagos Tortoise

  18. Darwin’s Focus on Adaptation • In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes • From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches

  19. LE 22-6 Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.

  20. In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar • 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

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

  22. Descent with Modification • The phrase descent with modification summarized Darwin’s perception of the unity of life • The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past • In the Darwinian view, the history of life is like a tree with branches representing life’s diversity

  23. LE 22-7 Sirenia (Manatees and relatives) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) Elephas maximus (Asia) Hyracoidea (Hyraxes) 0 Years ago 10,000 2 5.5 Stegodon Mammuthus Mammut Deinotherium Platybelodon Millions of years ago 24 Barytherium Moeritherium 34

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

  25. Observation #1: For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully

  26. Observation #2: 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

  27. Observation #4: Members of a population vary extensively in their characteristics; no two individuals are exactly alike

  28. 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

  29. 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

  30. Artificial Selection • In artificial selection, humans have modified other species over many generations by selecting and breeding individuals with desired traits

  31. LE 22-10 Lateral buds Terminal bud Brussels sprouts Cabbage Leaves Flower clusters Kale Cauliflower Stem Flowers and stems Kohlrabi Wild mustard Broccoli

  32. Summary of Natural Selection • Natural selection is differential success in reproduction from interaction between individuals that vary in heritable traits and their environment • Natural selection produces an increase over time in adaptation of organisms to their environment • If an environment changes over time, natural selection may result in adaptation to these new conditions Video: Seahorse Camouflage

  33. LE 22-11 A flower mantid in Malaysia A stick mantid in Africa

  34. 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

  35. Natural Selection in Action • Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug-resistant HIV

  36. Differential Predation in Guppy Populations • Researchers have observed natural selection leading to adaptive evolution in guppy populations

  37. LE 22-12a Pools with killifish but no 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”

  38. LE 22-12b 185.6 200 100 92.3 Control population: Guppies from pools with pike-cichlids as predators 85.7 161.5 160 80 Age of guppies at maturity (days) 58.2 Mass of guppies at maturity (mg) 120 60 48.5 76.1 67.5 80 40 Experimental population: Guppies transplanted to pools with killifish as predators 40 20 Females Females Males Males

  39. The Evolution of Drug-Resistant HIV • The use of drugs to combat HIV selects for viruses resistant to these drugs • The ability of bacteria and viruses to evolve rapidly poses a challenge to our society

  40. LE 22-13 100 Patient No. 1 Patient No. 2 75 Percent of HIV resistant to 3TC 50 Patient No. 3 25 0 2 12 4 8 6 10 0 Weeks

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

  42. Homology • Homology is similarity resulting from common ancestry

  43. Anatomical Homologies • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

  44. LE 22-14 Whale Bat Cat Human

  45. Comparative embryology reveals anatomical homologies not visible in adult organisms