Evolution is a change in allele frequencies over time

The frequency of an allele in a population changes over time - this is evolution.
Natural selection is one method by which evolution occurs. Here's a reminder of how it works:

Individuals of the same species vary because they have different alleles.
Predation, disease and competition (selection pressures) create struggle for survival.
Because individuals vary, some are better adapted to the selection pressures than others.
This means there are differential levels of survival and reproductive success in a population. Individuals are likely to survive, reproduce and pass on their genes than individuals with a different phenotype.
This means that a greater proportion of the next generation inherit the beneficial alleles.
They, in turn are more likely to survive, reproduce and pass on their genes.
So the frequency of the beneficial alleles in the gene pool increases from generation to generation.

	Created by Lucy Nove about 7 years ago

A2 Biology (Populations and Evolution) Note on Variation and Selection, created by Lucy Nove on 02/02/2017.