Types of Evolution
When we examine evolution as a process, we see certain patterns. It is helpful to discuss evolution in terms of these patterns to answer questions and make comparisons. These patterns include:
- Divergent evolution: This process refers to what is normally thought of as evolution, and what we have been discussing thus far. Divergent evolution occurs when individuals from one population evolve differently. This, as discussed above, can lead to speciation. For example, the brown bear and the polar bear had a common ancestor. Migration of the bears, leading to geographic isolation, resulted in adaptation to different environments. Divergent evolution often results in individuals having homologous structures, structures that have been adapted differently to perform different functions.
- Convergent evolution: When environments are similar or identical, the same selective pressures will be placed on the organisms that live in these environments. Therefore, different species in one environment (or two similar environments) will evolve similar structures to function in the environment. These structures are called analogous structures. One striking example of this is seen in sharks (fish), whales (mammals) and penguins (birds): although very distantly related, all have developed similar structures (fins) that allow them to function in the same environment (the ocean).
- Coevolution: Organisms that share an environment often evolve together due to the selective pressures placed on one or more species in the environment. Thus, one species often changes in response to the change in another species.