UNIT 07 / REVIEW

Natural Selection

Evolution has no plan. Neither did your last answer, apparently.

Active recall activities40 original questions · 7 topics

MAKE THE CONNECTION · SIMPLIFIED MODEL

Variation

Selection

Differential reproduction

Allele change

Use this overview to connect processes. Review the details below for mechanisms and exceptions.

01 / Natural selection

Heritable variation plus unequal reproductive success can change allele frequencies. Fitness is contribution to future generations in a particular environment.

Common trap: Survival is one component of fitness, not the entire definition. Surviving without reproducing contributes no alleles to the next generation.

02 / Hardy-Weinberg

For two alleles, p+q=1. Under Hardy-Weinberg assumptions, genotype frequencies are p², 2pq, and q².

Common trap: Do not plug the dominant phenotype frequency straight into p². Dominant-looking individuals may be homozygous or heterozygous.

03 / Genetic drift and gene flow

Genetic drift is chance change in allele frequency, especially important in small populations. Gene flow transfers alleles between populations.

Common trap: Drift is not a synonym for selection. Ask whether reproductive differences were associated with a trait or resulted from sampling chance.

04 / Evidence of evolution

Independent fossil, anatomical, developmental, geographic, and molecular evidence supports shared ancestry and evolutionary change.

Common trap: A similar function does not prove close ancestry. Evolution can arrive at comparable solutions in separate lineages.

05 / Phylogeny

Relatedness depends on the most recent common ancestor. Rotating branches around a node does not change a tree’s relationships.

Common trap: Do not count how many centimeters separate the tips. Read the branching pattern, Professor Talon begs you.

06 / Speciation

Speciation involves divergence of populations and reproductive isolation. Geographic separation can reduce gene flow but does not guarantee a new species.

Common trap: A river splitting a population is the start of a possible process, not automatic proof that two species appeared overnight.

07 / Origins and extinction

Evolutionary models distinguish the origin of organic molecules, heredity, cells, and later diversification. Extinction changes which lineages and niches persist.

Common trap: Evolution is branching history, not a march toward humans or an unavoidable increase in complexity.

Keep going

Original review notes informed by standard biology principles. Check the official AP Biology framework ↗ and OpenStax Biology 2e ↗ for further reading.