Chapter 16 Evidence of Evolution (Sections 16.1 - 16.5)

1. Chapter 16Evidence of Evolution (Sections 16.1 - 16.5)

2. 16.1 Reflections of a Distant Past • Events of the ancient past can be explained by studying physical, chemical, and biological processes • An asteroid impact may have caused a mass extinction 65.5 million years ago • mass extinction • Simultaneous loss of many lineages from Earth

3. The K-T Boundary Layer • A unique rock layer that formed worldwide 65.5 million years ago marks an abrupt transition in the fossil record which implies a mass extinction

4. 16.2 Early Beliefs, Confounding Discoveries • Expeditions by 19th century naturalists such as Alfred Wallace yielded increasingly detailed observations of nature • Geology, biogeography, and comparative morphology of organisms led to new ways of thinking about the natural world

5. Key Terms • naturalist • Person who observes life from a scientific perspective • biogeography • Study of patterns in the geographic distribution of species and communities • comparative morphology • Study of body plans and structures among groups of organisms

6. Biogeography • Traveling naturalists noted unexplained patterns in the geographic distribution of species • Plants and animals living in extremely isolated places looked similar to species living on different continents • Example: Three similar ratite birds – the emu of Australia, rhea of South America, and ostrich of Africa

7. Similar-Looking, Related Species

8. Similar-Looking, Related Species A Emu, native to Australia Fig. 16.2a, p. 238

9. Similar-Looking, Related Species B Rhea, native to South America Fig. 16.2c, p. 238

10. Similar-Looking, Related Species C Ostrich, native to Africa Fig. 16.2b, p. 238

11. Comparative Morphology • Naturalists also had trouble classifying organisms that are outwardly very similar, but quite different internally • Example: the American spiny cactus andAfrican spiny spurge live in similar environments, but are native to different continents – their reproductive parts are very different, so they can’t be as closely related they appear

12. Similar-Looking, Unrelated Species

13. Comparative Morphology • Other organisms that differ greatly in outward appearance may be very similar in underlying structure • Example: A human arm, a porpoise flipper, an elephant leg, and a bat wing have comparable internal bones

14. Vestigial Body Parts • Body parts that have no apparent function, such as leg bones in snakes and tail bones in humans, were also confusing

15. Vestigial Body Parts coccyx leg bones A Pythons and boa constrictors have tiny leg bones, but snakes do not walk. B We humans use our legs, but not our coccyx (tail bones). Fig. 16.4, p. 239

16. ANIMATION: Comparative pelvic anatomy To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

17. Fossils • Fossils of many animals that had no living representatives were also discovered • Deeper layers of rock held fossils of simple marine life; layers above them held similar but more complex fossils • fossil • Remains or traces of an organism that lived in the ancient past – physical evidence of ancient life

18. ANIMATION: Comparative anatomys To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

19. 16.3 A Flurry of New Theories • In the 1800s, many scholars saw evidence of evolutionand realized that life on Earth had changed over time • 19th century naturalists proposed theories such as catastrophismand inheritance of acquired characteristics in attempts to reconcile traditional beliefs with physical evidence

20. Key Terms • catastrophism • Now-abandoned hypothesis of Georges Cuvier, that catastrophic geologic forces unlike those of the present day shaped Earth’s surface • evolution • Change in a lineage, or descent with modification • lineage • Line of descent

21. Darwin and the HMS Beagle • In 1831, the 22-year-old Charles Darwin set sail as a naturalist aboard the Beagle, which circumnavigated the globe over a period of five years • Darwin’s detailed observations of geology, fossils, plants, and animals encountered on this expedition changed the way he thought about evolution

22. Voyage of the HMS Beagle

23. Theory of Uniformity • On his voyage, Darwin read Charles Lyell’s Principles of Geology, which gave him insights into the geologic history of the regions he would encounter on his journey • theory of uniformity • Idea proposed by Lyell that, over great spans of time, gradual, everyday geologic processes such as erosion could have sculpted Earth’s current landscape

24. Charles Darwin

25. Key Concepts • Emergence of Evolutionary Thought • Nineteenth-century naturalists started to think about the global distribution of species • They discovered similarities and differences among major groups, including those represented as fossils

26. 16.4 Darwin, Wallace, and Natural Selection • Darwin’s observations of species in different parts of the world helped him understand a driving force of evolution • Charles Darwin and Alfred Wallace independently came up with a theory of how environments also select traits

27. Old Bones and Armadillos • Darwin noticed that fossils of extinct glyptodons from Argentina had many traits in common with modern armadillos • The idea that they possibly shared an ancestor helped Darwin develop a theory of evolution by natural selection

28. Ancient Relatives • A modern armadillo, about a foot long • Fossil glyptodon, an automobile-sized mammal that lived between 2 million and 15,000 years ago

29. Competition for Limited Resources • Thomas Malthus’s wrote that a population tends to grow until it exhausts environmental resources • As that happens, competition for those resources intensifies among the population’s individuals • Darwin realized that all populations, not just human ones, must have the capacity to produce more individuals than their environment can support

30. A Key Insight: Variation in Traits • Darwin realized that in any population, some individuals have traits that make them better suited to their environment than others – and those traits might enhance the individual’s ability to survive and reproduce (fitness) • Adaptive traits (adaptations)that impart greater fitnessto an individual would become more common in a population over generations, compared with less competitive forms

31. Key Terms • fitness • Degree of adaptation to an environment, as measured by an individual’s relative genetic contribution to future generations • adaptation (adaptive trait) • A heritable trait that enhances an individual’s fitness

32. Natural Selection • Darwin considered the way humans select desirable traits in animals by selective breeding (artificial selection) • Darwin called the process in which environmental pressures result in the differential survival and reproduction of individuals of a population natural selection • Darwin published On the Origin of Species, which laid out the theory of evolution by natural selection

33. Key Terms • artificial selection • Selective breeding of animals by humans • natural selection • A process in which environmental pressures result in the differential survival and reproduction of individuals of a population who vary in details of shared, heritable traits

34. Principles of Natural Selection

35. Great Minds Think Alike • Alfred Wallace studied wildlife in the Amazon and Malay Archipelago • Before Darwin published, Wallace wrote an essay outlining evolution by natural selection—the same theory as Darwin’s

36. Key Concepts • A Theory Takes Form • Evidence of evolution, or change in lines of descent, led Charles Darwin and Alfred Wallace to independently develop a theory of natural selection • The theory explains how traits that define each species change over time

37. ANIMATION: Finches of the Galapagos To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

38. 16.5 Fossils: Evidence of Ancient Life • Fossils are remnants or traces of organisms that lived in the past • Most fossils are mineralized bones, teeth, shells, seeds, spores, or other hard body parts • Trace fossils such as footprints and other impressions, nests, burrows, trails, eggshells, or feces are evidence of an organism’s activities

39. Process of Fossilization • Fossilization begins when an organism or its traces become covered by sediments or volcanic ash • After a very long time, pressure and mineralization transform the remains into rock • Fossils are found in stacked layers of sedimentary rock • Younger fossils occur in more recent layers, on top of older fossils in older layers

40. The Fossil Record • Fossils are relatively rare, so the fossil record will always be incomplete • For a fossil of an extinct species to be found, at least one specimen had to be buried before it decomposed or something ate it • The burial site had to escape destructive geologic events, and it had to be a place accessible enough for us to find

41. The Ancient Lineage of Whales • The fossil record holds clues to evolution: • Ancestors of whales probably walked on land • The skull and lower jaw have characteristics similar to those of ancient carnivorous land animals • With their artiodactyl-like ankle bones, Rodhocetus and Dorudon were probably offshoots of the artiodactyl-to-modern-whale lineage

42. The Ancient Lineage of Whales

43. The Ancient Lineage of Whales Fig. 16.9a, p. 244

44. The Ancient Lineage of Whales A 30-million-year-old Elomeryx. This small terrestrial mammal was a member of the same artiodactyl group that gave rise to hippopotamuses, pigs, deer, sheep, cows, and whales. Fig. 16.9a, p. 244

45. The Ancient Lineage of Whales Fig. 16.9b, p. 244

46. The Ancient Lineage of Whales BRodhocetus, an ancient whale, lived about 47 million years ago. Its distinctive ankle bones point to a close evolutionary connection to artiodactyls. Fig. 16.9b, p. 244

47. The Ancient Lineage of Whales Fig. 16.9c, p. 244

48. The Ancient Lineage of Whales C Dorudon atrox, an ancient whale that lived about 37 million years ago. Its artiodactyl-like ankle bones were much too small to have supported the weight of its huge body on land, so this mammal had to be fully aquatic. Fig. 16.9c, p. 244

49. The Ancient Lineage of Whales Fig. 16.9d, p. 244

50. The Ancient Lineage of Whales D Modern cetaceans such as the sperm whale have remnants of a pelvis and leg, but no ankle bones. Fig. 16.9d, p. 244