2.1 modes of selection

• struggle for existence/survival of the fittest → WRONG

Relative fitness

• contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

• how many of genes are getting passed on

  • survive

  • have babies

  • babies survive and have babies

modes of selection

• normal distribution of a phenotype

Directional selection

• conditions favor individuals exhibiting one extreme of the trait

• mean shifts

stabilizing selection

• favors intermediate phenotype and extremes selected against

• same mean, reduced variance

disruptive selection

• conditions favor both extremes of the phenotype, intermediate selected against

• same mean, increased variance

sexual selection

• one sex chooses favorable traits in the other

• female choice because of increased reproductive investment

• members of the same sex compete w/ e/o

  • intimidate, deter, fight

• sexual dimorphism → difference in size/appearance between sexes

artificial selection

• breed for desirable traits