1. I got nothin’ witty. Evolutionary Theory

2. How evolution takes place BIG IDEA: The theory of evolution is constantly changed as new evidence is discovered. One thing is known – evolution occurs at the population level. There are five major mechanisms of evolution: There are five major mechanisms of evolution: 1. Gene flow – caused by organisms migrating in or out of a population 2. Mutations – random changes in DNA 3. Natural selection 4. Nonrandom mating – you pick your mate for a reason 5. Genetic drift (next slide) Hardy-Weinberg equilibrium Without these, a population will reach Hardy-Weinberg equilibrium (meaning the percent of each allele will stay the same) and evolution will not occur.

3. Genetic drift This occurs when you have a small population and the genes in the gene pool become skewed as a result. Example one: founder effect Example one: founder effect – when a small population moves to an isolated area and interbreeds within itself (like Darwin’s finches) Example two: bottleneck effect Example two: bottleneck effect – when species numbers dwindle down to a low amount and increase again (like cheetahs)

4. Natural Selection types Stabilizing selection Stabilizing selection (common) – the average form of an organism is selected(ex: birth size) Directional selection Directional selection – one of the two extremes is selected (ex: pepper moths) Disruptive selection Disruptive selection – both extremes are selected – the average selected against (ex: Northern water snake)

5. Speciation Q: How do you know when you have a new species? Q: How do you know when you have a new species? A: When some members of a population can no longer breed and produce fertile offspring with members of the original population. A: When some members of a population can no longer breed and produce fertile offspring with members of the original population. prezygoticpostzygotic sympatric speciation The sexual isolation that arises in this process can be prezygotic (before fertilization) or postzygotic (after). This would lead to sympatric speciation (new species arise within a population) allopatric speciation Speciation can also be caused by geographic boundaries where the organisms can’t breed (allopatric speciation)

6. Evolution types Divergent evolution Divergent evolution – many new species arise from a common ancestor due to unique adaptations (i.e. adaptive radiation). Coevolution Coevolution – two or more species evolving in close relationship to one another. Convergent evolution Convergent evolution – species evolving similarly, despite being separated geographically.