Chapter 22: Descent with Modifications

1. Chapter 22: Descent with Modifications Barbara Musolf Clayton State University Administration Building A 16-C 678-466-4851

2. Objectives • Develop an historical understanding of the Darwinian Revolution • Natural selection is one of the mechanisms that underlies evolutionary changes in populations. • Proof that natural selection is powerful mechanism is its ability to explain changes in populations. • Understand the difference between hypothesis and theory.

3. Charles Darwin February 12, 1809 to April 19, 1882

4. Darwin’s Theory • The mechanism of natural selection lies behind the evolutionary process. • The adaptation of organisms to their environment leads to the accumulation of genetic traits. • Darwin presented evidence that modern organisms evolved from ancestral species.

5. The Origin of Species 11/22/1859 • Descent with modification (Evolution) explains the diversity of species from the past to the present. • Natural selection is the mechanism underlying adaptive evolution. • Evolution implies ancestral organisms that give rise to new organisms. • Organisms are unified by this descent from a common ancestor.

6. Descent with Modification

7. Natural Selection and Adaptation Ernst Mayr presented Darwin’s logic • Observation #1: Population sizes would increase exponentially if all individuals successfully reproduced. • Observation #2: Populations remain stable in size with the exception of seasonal fluctuations.

8. Natural Selection and Adaptation Darwin’s logic • Observation #1: Members of a population vary in their characteristics • Observation #2: Traits are heritable from parents to offspring

9. Natural Selection and Adaptation Darwin’s logic • Observation #3: All species are capable of producing more offspring than their environment can support.

10. Natural Selection and Adaptation Darwin’s logic • Observation #4: Lack of food or other resources leads to survival of only a few offspring. • Inference #1: Individuals with inherited traits that allow them to survive and reproduce will leave behind more offspring that less fit individuals. • Inference #2: The unequal ability of individuals to survive can lead to gradual changes in the characteristics of a population.

11. The influence of Malthus • Malthus contended that the growth in human populations exceeds the available resources. • All organisms tend to overreproduce • Environmental factors favor some heritable traits over others. • Those with favorable traits tend to produce more offspring.

12. Artificial selection Terminal bud Lateral buds Cabbage Brussels sprouts Leaves Flower clusters Kale Cauliflower Stem Flowers and stems Broccoli Kohlrabi Wild mustard

13. Summary of Natural Selection • Natural selection is the reproductive success of an individual with particular heritable traits within a particular environment. • The population changes over time to adapt successfully to its environment. • Environmental changes can lead to selection of different heritable traits that can give rise to a new species. • Populations evolve NOT individuals

14. The explanatory power of Darwin’s theory of evolution The study of wild guppy populations in the Aripo River system in Trinidad Observation: Brightly colored males are more attractive to females, however they are also more conspicuous and can attract predators.

15. The explanatory power of Darwin’s theory of evolution

16. The explanatory power of Darwin’s theory of evolution The study of wild guppy populations in the Aripo River system in Trinidad, Endler Hypothesis: Intense predation causes selection of male guppies with drab coloration. Test: Transplanted 200 guppies from pike-cichlid ponds to killifish ponds that had no guppies.

17. The explanatory power of Darwin’s theory of evolution • Results: After 22 months and 15 generations…

18. The explanatory power of Darwin’s theory of evolution Drug Resistant HIV: Evolution of HIV to the drug 3TC

19. The explanatory power of Darwin’s theory of evolution • Natural selection is more an editing process than a creative process. • Natural selection depends on time and place, which in the end is a dependency on the conditions of the current environment.

20. Fossil evidence • Change in location of and angle of spines on head

21. Transition to sea life • Hypothesis: Cetaceans evolved from terrestrial species • Predictions can be tested using radioactive dating.

22. Homology • Homologies are similarities found in different organisms that arise because of a common ancestry. • Anatomical homologies such as the arrangement of the forelimb in ALL mammals. • Homologous structures seen during development often have very different functions. • Explains the presence of vestigial limbs on snakes.

23. Homology in mammalian forelimbs

24. Homology in vertebrate embryos

25. Homologies and Evolutionary trees

26. LE 22-17 Convergent evolution and analogous structures NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel

27. Biogeography • Biogeography is the geographic distribution of organisms. • Geography affects the dispersal ability of organisms. • Continental drift • Islands provide the best evidence for an environment’s influence on an organism. • Islands have numerous endemic species. • These species are closely related to species on nearby mainlands

28. Theory • The theory of evolution explains results from many observations and experiments. • Theories stand up to thorough testing, explains many scientific results, and can be observed in nature. • Additions can be made to the theory. Natural selection is likely not the only mechanism operating as an organism evolves.