Evidence supporting theory of evolution

1. Evidence supporting theory of evolution • Analogous structures • Structures similar in form and function. • Develop as a result of convergent evolution?

2. Evidence supporting theory of evolution • Life’s chemistry • Organisms are made of molecules and studying the molecules can help us understand possible relationships. • Example: Proteins • Made of amino acids bonded together. • Similar to a strand of pearls. • More closely related two organisms are, the more closely their proteins resemble each other.

3. Speciation • Speciation: species giving rise to new species. • Some segment of original population must be isolated from the rest. • Reproductive isolation is an essential ingredient. • Occurs via two mechanisms: • Allopatric Speciation • Sympatric Speciation

4. Allopatric speciation • Definition: Speciation that occurs between isolated populations. • Originated in different fatherlands. • Must be geographically isolated.

5. Allopatric speciation • To reach and colonize new area, must realize three opportunities: • Geographic • Physiological • Ecological

6. Sympatric speciation • Definition: Speciation among populations whose ranges overlap. • Occur in same fatherland. • Can occur with species occupying different habitats, but in the same range.

7. Both types of speciation can be occurring at the same time. • Initially population is geographically isolated. • If geographic barrier is removed, populations overlap. • Could still be isolated by differences in preferred habitat, courtship displays, breeding season, preferred.

8. If not isolated by differences, then two populations will merge into one species.

9. Patterns in Evolution • Convergent evolution • Unrelated species living in similar environments and facing similar environmental challenges sometimes evolve similar characteristics.

10. Patterns in Evolution • Divergent evolution • Closely related species living in different environments and facing different environmental challenges sometimes evolve dissimilar characteristics.

11. Patterns in Evolution • Adaptive radiation • Sometimes, several species will evolve from a single, ancestral species.

12. Patterns in Evolution • Coevolution • Evolution of one species affects the evolution of another species. • As predators evolve, prey evolves. As prey evolves, predators evolve. • Example: Cheetahs feed on Thompson’s gazelles • As the speed of one population of cheetahs improves so does the speed of the Thompson’s gazelles .

13. Patterns in Evolution • Gradualism • Evolution may occur as a slow, gradual process of change. • Theory favored by early evolutionists.

14. Patterns in Evolution • Punctuated equilibrium • Evolution may proceed with long periods of relatively little change (stasis) punctuated with short periods of intense change. • Examples: House flies, trilobites, antibiotic-resistant bacteria.

15. Evolution does not always occur • Natural selection can only work on existing variation. • Variation cannot be created on demand. • Some species lack range of variation to support evolution.

16. Results of evolution • Everywhere we look on the Earth, you can find organisms. • Scientists have described 1.5 millions species • Still many species yet to be described. • Predictions indicate there may be 10-100 times as many species as those already described.

17. Darwin’s Theory Debated • Three main criticisms: • Darwin lacked direct evidence for natural selection. • Indirect evidence was unconvincing • Darwin could not explain the source of variation in a population and inheritance of variation. • Answered by an understanding of genetics • What is the rate at which organisms evolve? • Slow and continuous or jerky and discontinuous?

18. Darwin recognizes three special cases of natural selection • Sexual selection explained flamboyant appearance amongst birds. • Sexual selection: female birds choose mates and are attracted to males with extreme features. • Females breed with them and extreme features passed to offspring.

19. Darwin recognizes three special cases of natural selection • Altruism • Individual behavior benefits a social group often at the expense of the individual. • Example: worker bees in a hive • Kin Selection • Individuals help kin raise their young.