Patterns of Evolution

directional selection

for a extreme trait against other extreme

stabilizing selection

for moderate traits against both extremes

distributive selection

for both extreme traits against moderate traits

mutation

change in genetic material (DNA)

what causes mutations?

by chance or enviormental factors

useful mutations

maintained in the population

migration/gene flow

the movement of individuals in/out of population

allopatric speciation

a barrier causes two new groups to form

Adaptive Radiation

over relatively fast time, species may split into separate species from one original ancestor

Extinction

when all members of a species die off or fail to reproduce

Gradualism

species slowly & steadily change through a series of small changes

Punctuated Equilibrium

 long periods of stability in a species are “punctuated” by periods of rapid evolution