Natural+Selection+Note

Natural Selection
The process whereby some individuals in a population have higher levels of //reproductive success// than others.

Therefore, over many generations a species changes as different traits become "popular" (beneficial), i.e., survival of the luckiest

Factors such as //predators//, //parasites//, and //competition for resources// act as a **selective pressure**


 * Selective Pressure** is any //environmental// condition that selects ("chooses") //for// certain characteristics //and// it selects //against// other characteristics.

e.g 1. In a forest with tall tress young trees that are small and able to survive in shade will live long enough to grow and pass on their alleles (genes). In the next generation the alleles responsible for being able to survive in shade will increase in frequency in the population.

Over time the tree population will be better able to survive in the shade because of selective pressure that favours shade-tolerance

e.g. 2. Ability to digest milk in adult humans. Only a small proportion of humans can do so, and, that ability evolved in societies where dairy was readily available.