Darwin and Evolution

1. Darwin and Evolution Chapter 17

2. History of Evolutionary Thought • Prior to Darwin, most people had a mindset determined by deep-seated beliefs held to be intractable truths • Biology during preceding century had slowly begun to accept the idea of evolution • Living things share common characteristics due to common ancestry Mader: Biology, 9th Ed.

3. Mid-Eighteenth Century Taxonomy was an important endeavor during mid-eighteenth century • Carolus Linnaeus • Special creation – each species has an ideal structure and function • Fixity of species – each species had a place in the scala naturae(sequential ladder of life) Mader: Biology, 9th Ed.

4. Mid-Eighteenth Century Count Buffon wrote 44-volume natural history describing all known plants and animals • Provided evidence of descent with modification • Influences of the environment, migration, geographical isolation, and the struggle for existence Mader: Biology, 9th Ed.

5. Mid-Eighteenth Century Erasmus Darwin • Suggested common descent based on: • Changes undergone by animals during development • Artificial selection by humans • The presence of vestigial organs Mader: Biology, 9th Ed.

6. Late Eighteenth Century George Cuvier • First to use comparative anatomy to develop a system of classification • Founded Paleontology • Proposed Catastrophism • Hypothesized local catastrophes had occurred whenever a new strata showed a new mix of fossils • After each catastrophe, a region was repopulated by species from surrounding areas. Mader: Biology, 9th Ed.

7. Late Eighteenth Century Lamarck • First biologist to believe evolution occurs • First to link diversity with environmental adaptation • Concluded more complex organisms are descended from less complex organisms • Inheritance of acquired characteristics (Lamarckianism) • Giraffes stretch necks and then pass on long necks to offspring Mader: Biology, 9th Ed.

8. Late Eighteenth Century Charles Lyell • Supported a theory that the earth was subject to slow but continuous cycles of erosion and uplift • Uniformitarianism rates and processes of change are constant Mader: Biology, 9th Ed.

9. Darwin’s Theory of Evolution Mader: Biology, 9th Ed.

10. Darwin’s Theory of Evolution • Occurrence of Descent • Darwin was not convinced of uniformitarianism, but did believe the earth was very old • Enough time for descent with modification Mader: Biology, 9th Ed.

11. Biogeography • Biogeography is the study of the geographic distribution of lifeforms on earth • Darwin saw how similar species in similar habitats • Reasoned related species could be modified according to the environment Mader: Biology, 9th Ed.

12. Galápagos Islands • Tortoises • Darwin noticed tortoise neck length varied from one island to next • Proposed that tortoise speciation on islands could be correlated with a difference in vegetation among the islands Mader: Biology, 9th Ed.

13. Galápagos Islands • Finches • Darwin observed different species of finches on various islands • Speculated that all the different types of finches could have descended from a single type of mainland finch Mader: Biology, 9th Ed.

14. Natural Selection and Adaptation • Natural selection proposed as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation Mader: Biology, 9th Ed.

15. Three Preconditions for Natural Selection • Individuals have heritable variations • Many more individuals are produced each generation than the environment can support • Some individuals have adaptive characteristics enabling increased survival and reproduction Mader: Biology, 9th Ed.

16. Two Consequences of Natural Selection • Increasing proportion of succeeding generations have these characteristics • Populations become adapted to their local environment Mader: Biology, 9th Ed.

17. Organisms Have Variations • Darwin emphasized members of a population vary in their functional, physical, and behavioral characteristics • Believed variations were essential • New variations as likely to be helpful as harmful • Heritable variations allow adaptation to the environment Mader: Biology, 9th Ed.

18. Variation in a Population Mader: Biology, 9th Ed.

19. Organisms Struggle to Exist • Malthus stressed the reproductive potential of human beings • Proposed death and famine were inevitable due to rapid population growth • Each generation has the same reproductive potential as the previous generation • Constant struggle for existence Mader: Biology, 9th Ed.

20. Organisms Differ in Fitness • Fitness is the relative reproductive success of an individual • Most-fit individuals capture a disproportionate amount of resources • In nature, interactions with the environment determine which members of a population reproduce to a greater degree • Artificial Selection Mader: Biology, 9th Ed.

21. Artificial Selection Mader: Biology, 9th Ed.

22. Artificial Selection in Plants Mader: Biology, 9th Ed.

23. Organisms Become Adapted • An adaptation is a trait that helps an organism become more suited to its environment • Product of natural selection Mader: Biology, 9th Ed.

24. The Evidence of Evolution • Fossil Evidence • Fossil record is the history of life recorded by remains from the past • Documents a succession of life forms from the simple to the more complex • Sometimes the fossil record is complete enough to allow a trace of the evolutionary history of an organism Mader: Biology, 9th Ed.

25. Transitional Fossils Mader: Biology, 9th Ed.

26. Mader: Biology, 9th Ed.

27. Biogeographical Evidence • Distributions of many plants and animals across earth consistent with hypothesis that when forms are related, they evolved in one locale and then spread to accessible regions • Marsupials Mader: Biology, 9th Ed.

28. Biogeography Mader: Biology, 9th Ed.

29. Anatomical Evidence • Darwin was able to show a common descent hypothesis offers a plausible explanation for anatomical similarities among organisms • Despite dissimilar functions, all vertebrate forelimbs contain the same sets of bones in similar ways Mader: Biology, 9th Ed.

30. Anatomical Evidence • Homologous Structures are anatomically similar because they are inherited from a common ancestor • Analogous Structures serve the same function, but are not constructed similarly, and do not share a common ancestor • Vestigal Structures are fully-developed anatomical structures developed in one group of organisms, but reduced, and may have no function, in similar groups Mader: Biology, 9th Ed.

31. Significance of Homologous Structures Mader: Biology, 9th Ed.

32. Significance of Developmental Similarities Mader: Biology, 9th Ed.

33. Biochemical Evidence • Almost all living organisms • Use the same basic biochemical molecules • Utilize same DNA triplet code • Utilize same 20 amino acids in their proteins • When the degree of similarity in DNA base sequences are compared, the data suggest common descent • When very similar, suggest recent common descent • When more different, suggest more ancient common descent Mader: Biology, 9th Ed.

34. Biochemical Differences Mader: Biology, 9th Ed.

35. Mader: Biology, 9th Ed. www.dinosauria.com/gallery/joe/joe3.html