Mechanisms of Evolution

Evolution – a change in the population’s gene pool over time These changes can be caused by: Genetic drift Natural selection

The gene pool has changed, evolution has occurred. Genetic Drift – a change in the gene pool caused by chance Ex: A natural disaster removes all but a few members of the population. Result: The remaining individuals have a smaller gene pool, some variations may have been lost. The next generation will lack those variations. The gene pool has changed, evolution has occurred.

Migration will also change the gene pool. Immigration will add genes to the gene pool Emigration will decrease the gene pool

Natural Selection- Overproduction occurs in all species Variations occur in all species Struggle for survival- resources are limited, not all born will survive Survival of the fittest- those best adapted to their environment will survive and reproduce.

How do variations occur? Viruses alter a cell’s DNA Chemicals and radiation can cause mutations If this occurs in the egg or sperm it will be passed to the offspring Sexual reproduction causes a mixing of genes

Fitness: ability of an individual to survive and reproduce - central to the process of Evolution - individuals with low fitness either die or produce few offspring

Adaptation: Inherited characteristic that increases an organisms chance for survival Ex: Speed, Camouflage, Claws, etc.

Evolution is driven by environmental change. As the environment changes, different adaptations will increase fitness. Adaptations that decrease fitness will eventually die out of the gene pool.

Evolution of pesticide resistance in response to selection