|
|
Rates of Evolution
|
Lecture 10
2/27/98
|
| | Today, we continue our investigation of evolution by focusing on the rates of speciation. |
| | We will use this discussion as a back drop for looking at the Cambrian Explosion |
| | Earths history shows periods of slow evolution punctuated by periods of rapid evolution |
| | The rate of evolution is dependent on at least three different things |
| | rate of environmental change |
| | Once structures and/or behaviors evolve it is difficult to change them radically |
| | Seven major animal groups appear in short period of geologic time |
| | Additional groups appear, but do not survive long |
| | By comparison, the rest of the earths history is one of slow evolution |
| | Speciation typically occurs when a small population is isolated from the main gene pool |
| | Selection that each population experiences varies. |
| | Over time genetic variability between the two populations grows to a point of where they can no longer interbreed |
| | Two primary factors govern the rate of speciation |
| | a positive force, providing new genetic material |
| | a negative force, removing mutations that are not beneficial |
| | Selection can be viewed as competition between individuals |
| | Competition between members of the same species |
| | Competition between members of different species |
| | new species form in a "filled" environment |
| | leads to normal rates of evolution |
| | new species form in an empty environment |
| | competition between species is minimal but increases with time. |
| | differences are preferentially selected for |
| The role of environmental change |
| A look back at the Cambrian Explosion |
| | Development of the SuperWorms |
| | Oxygenation of the upper sediments |
| | Escape to the surface (Base of the Cambrian) |
|
|
