Chapter 19
The Evolution of Populations
By Boundless
![Thumbnail](../../../../../figures.boundless-cdn.com/19037/square/figure-19-00-01.jpeg)
Genetic variation in a population is determined by mutations, natural selection, genetic drift, genetic hitchhiking, and gene flow.
![Thumbnail](../../../../../figures.boundless-cdn.com/27357/square/824px-abo_blood_type.jpg.jpg)
Population genetics is the study of the distributions and changes of allele frequency in a population.
![Thumbnail](../../../../../figures.boundless-cdn.com/19038/square/figure-19-01-01.jpg)
The Hardy-Weinberg principle can be used to estimate the frequency of alleles and genotypes in a population.
![Thumbnail](../../../../../figures.boundless-cdn.com/20514/square/coquina-variation3.jpeg)
Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population.
![Thumbnail](../../../../../figures.boundless-cdn.com/27460/square/random_genetic_drift_chart.jpg)
Genetic drift is the change in allele frequencies of a population due to random chance events, such as natural disasters.
![Thumbnail](../../../../../figures.boundless-cdn.com/19041/square/figure-19-02-04.jpeg)
A population's genetic variation changes as individuals migrate into or out of a population and when mutations introduce new alleles.
![Thumbnail](../../../../../figures.boundless-cdn.com/27471/square/1024px-american_robin_close-up.jpg)
Population structure can be altered by nonrandom mating (the preference of certain individuals for mates) as well as the environment.
![Thumbnail](../../../../../figures.boundless-cdn.com/27472/square/evolution_sm.jpg)
Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
![Thumbnail](../../../../../figures.boundless-cdn.com/27333/square/directional selection.jpg)
Stabilizing, directional, and diversifying selection either decrease, shift, or increase the genetic variance of a population.
![Thumbnail](../../../../../figures.boundless-cdn.com/19047/square/figure-19-03-02.jpeg)
In frequency-dependent selection, phenotypes that are either common or rare are favored through natural selection.
![Thumbnail](../../../../../figures.boundless-cdn.com/27474/square/ribbon-tailed_astrapia.jpg)
Sexual selection, the selection pressure on males and females to obtain matings, can result in traits designed to maximize sexual success.
![Thumbnail](../../../../../figures.boundless-cdn.com/20529/square/rphism-in-cepaea-nemoralis.jpeg)
Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.