Evidence of Evolution

1. Evidence of Evolution Chapter 17

2. Impacts, IssuesMeasuring Time • Evidence of events that happened millions of years ago – such as meteor impacts – lead to inferences about evolution of life on Earth

3. 17.1 Early Beliefs, Confounding Discoveries • Belief systems are influenced by the extent of our knowledge • Beliefs that are inconsistent with systematic observations of the natural world tend to change over time

4. Naturalists and Biogeography • Aristotle was one of first naturalists – people who observe life from a scientific perspective • In the late 1800s, Alfred Wallace and others were pioneers in biogeography – the study of patterns in the observation of species

5. Patterns in Biogeography

6. Comparative Morphology • Comparative morphologists study body plans and structures among groups of organisms • Some organisms are outwardly similar, but different internally; others differ outwardly, but have similar internal structures • Some organisms have vestigial parts with no apparent function

7. Vestigial Body Parts

8. coccyx limb bud Fig. 17-3, p. 261

9. Geology • Geologists found identical sequences of rock layers in different parts of the world • Different layers held different fossils – evidence of earlier forms of life • Cumulative findings from biogeography, comparative morphology, and geology led to new ways of thinking about the natural world

10. Fossils

11. 17.2 A Flurry of New Theories • By the 1800s, many scholars realized that life on Earth had changed over time, and began to think about what could have caused the changes

12. New Evidence and Old Beliefs • Catastrophism • Georges Cuvier proposed that many species that once existed became extinct due to catastrophic geological events unlike those known today • Gradualism • Jean-Baptiste Lamarck proposed that individuals changed in response to their environment, and passed those changes on to their descendents

13. Reconsidering Old Beliefs • Theory of uniformity • Lyell’s book, Principles of Geology, proposed that gradual, repetitive geological processes shaped the Earth over great spans of time • Lyell’s insights shaped Charles Darwin’s thinking during his five-year voyage on the Beagle

14. Voyage of the Beagle • Darwin observed unusual fossils and diverse species in a range of habitats

15. Beagle and The Galapagos Islands

16. 17.1-17.2 Key ConceptsEmergence of Evolutionary Thought • Long ago, naturalists started to catalog previously unknown species and think about the global distribution of all species • They discovered similarities and differences among major groups, including those represented as fossils in layers of sedimentary rock

17. 17.3 Darwin and Natural Selection • Darwin’s observations of species in different parts of the world helped him understand a driving force of evolution – natural selection

18. Old Bones and Armadillos • Darwin observed similarities between fossil glyptodons in Argentina and the armadillo

19. A Key Insight – Variation in Traits • Darwin’s observations: • Populations can produce more individuals than their environment can support • Some versions of a trait might enhance an individual’s ability to survive and reproduce in its particular environment • Example: Finches in the Galapagos Islands

20. Finches in the Galapagos Islands

21. Natural Selection • Natural selection • Differential survival and reproduction among individuals of a population that vary in details of shared, inherited traits • Adaptive trait • Any trait that enhances an individual’s fitness (ability to survive and reproduce in a particular environment)

22. Principles of Natural Selection

23. Stepped Art Table 17-1, p. 265

24. 17.4 Great Minds Think Alike • Darwin’s insights into evolution were made possible by contributions of scientists who preceded him • Alfred Wallace independently developed the idea of evolution by natural selection

25. Alfred Wallace • Wallace drew on his own observations of plant and animal species and proposed that natural selection is a driving force of evolution

26. 17.3-17.4 Key ConceptsA Theory Takes Form • Evidence of evolution, or changes in lines of descent, gradually accumulated • Charles Darwin and Alfred Wallace independently developed a theory of natural selection to explain how heritable traits that define each species evolve

27. 17.5 About Fossils • Fossils are remnants or traces of organisms that lived in the past • They give us clues about evolutionary relationships • The fossil record will always be incomplete

28. Fossils • Fossils • Remains of bones, teeth, shells, seeds, spores, or other body parts • Trace fossils • Evidence of an organism’s activities (nests, trails, footprints, burrows, bore holes, eggshells, feces)

29. Fossils

30. Fig. 17-9a, p. 267

31. Fig. 17-9b, p. 267

32. Fig. 17-9c, p. 267

33. How Do Fossils Form? • Organisms or traces are covered in sediments or volcanic ash • Inorganic compounds dissolved in water slowly replace minerals in bones and hard tissues • Pressure and mineralization transform remains into rocks

34. Fossil-Containing Sedimentary Rock • The oldest fossils are usually in the deepest layers of sedimentary rocks

35. The Fossil Record • The fossil record will never be complete • Geologic events obliterated much of it • Slanted toward species with hard parts, dense populations, wide distribution, long periods of time • Substantial enough to help reconstruct patterns and trends in the history of life, and establish some lines of descent (lineages)

36. 17.6 Dating Pieces of the Puzzle • Researchers use predictable radioisotope decay to estimate the age of rocks and fossils • Radiometric dating • Reveals the age of a material by determining its radioisotope and daughter element content

37. Radioisotopes • Radioisotope • A form of an element with an unstable nucleus • Decays into atoms of another element • Example: uranium 238 →lead 206 • Half-life • The time it takes for half of a radioisotope’s atoms to decay into a daughter element

38. Half-Life

39. parent isotope newly formed rock daughter isotope after one half-life after two half-lives Fig. 17-11, p. 268

40. parent isotope newly formed rock daughter isotope after one half-life after two half-lives Stepped Art Fig. 17-11, p. 268

41. Animation: Radioisotope decay

42. Carbon 14 Dating

43. Animation: Radiometric dating

44. 17.7 A Whale of a Story • New fossil discoveries are continually filling the gaps in our understanding of the ancient history of many lineages

45. New Links in the Ancient Lineage of Whales

46. New Links in the Ancient Lineage of Whales

47. New Links in the Ancient Lineage of Whales

48. 17.5-17.7 Key ConceptsEvidence From Fossils • The fossil record offers physical evidence of past changes in lines of descent • We use the property of radioisotope decay to determine the age of rocks and fossils

49. 17.8 Putting Time into Perspective • Geologic time scale • The chronology of Earth’s history • Measured by radiometric dating and fossils in similar sequences of sedimentary rock layers around the world

50. The Geologic Time Scale