Principles of Evolution

1. Principles of Evolution Chapter 15

2. Objectives • Be familiar with the concept of evolution • Understand what mechanisms contribute to the evolution of species • Describe the forms of evidence that support evolution as a process

3. Evidence for Evolution • Evolution is best described as genetic change occurring within a organisms over time • Evolution is supported by several types of evidence including • Fossil • Comparative Anatomy and Development • Biochemical evidence

4. Evolutionary Evidence • Fossil Evidence • A Fossil is the historic remains of a formally living organism e.g., footprint, droppings, or bones • Fossils buried deeper in the ground are presumed to be older due to stratification of sediments. • By examining the fossil evidence, scientists can visualize repeated extinction events followed by proliferation of new organisms. • Mass extinctions occur about every 26 million years

5. Evolutionary Evidence • Embryonic Development • Phylogeny tends to recapitulate ontogeny or; the relatedness of two organisms may be reflected in their development and anatomy. • Homologous structures within species reflect common genes. Homologous means the structures and develop by similar processes during formation. • Vestigialstructures (those that have lost their function, e.g., appendix, male breast, tailbone) also reflect common ancestry. (Snakes with hips) • Closely related organisms share a similar embryological development e.g. all vertebrates develop a notochord (backbone) and pharyngeal (gill) pouches.

6. Evolutionary Evidence • All living organisms share a similar biochemistry (DNA, ATP, RNA, Enzymes). • The relatedness of two organisms is reflected in their biochemistry; the closer the relationship, the closer the AA or base sequences. • Species that are not believed to be closely related have greater differences in their biochemistry

7. What Causes Evolution To Occur? • Genetic Change • Mutations can give rise to new alleles • Crossover, Independentassortment and Fertilization result in the recombination of genetic material • Natural Selection: Some organisms survive and reproduce at a higher rate than other organisms. • Result of the inheritance of particular characteristics • Genetic Drift: A chance event that shapes the genetic makeup of a group of organisms

8. Natural Selection (p270-272,292-295) • Survival of the fittest • Four Criteria must be met • Genetic variation of members within a population • Inheritance of differences between individuals • Differential Adaptedness: adaptations reflected in the differences • Differential Reproduction: better adapted individuals are more likely to reproduce or transfer their genes to next generation. First proposed by Charles Darwin after reading the paper of Alfred Wallace

9. Natural Selection can change populations in 3 ways a) Directional Selection: b) Diversifying Selection: c) Stabilizing Selection:

10. Genetic Drift (286-289) • Genetic Drift: change in allele frequencies within a gene pool due to chance. • As population gets small some genotypes may not participate in random mating events. This may increase the frequency of expression of some traits. • Founder effect – island species • Bottleneck effect – Cheetah, Elephant Seal