AP Biology Notes: Evolution

Five Things to Know about Evolution: 

  1. Evolution is shaped by a number of mechanisms, including selective pressures, sources of variation, and random effects, such as genetic drift.
  2. Biological species concept: a species is a reproductively isolated population able to interbreed and produce fertile offspring.
  3. In allopatric speciation, geographically separated populations develop into different species. Sympatric speciation occurs when populations in the same environment adapt to fill different niches. Parapatric speciation occurs with limited interbreeding between two groups.
  4. Evidence for evolution comes from comparative anatomy (homologous and analogous structures), biogeography, embryology, the fossil record, biological classification, and molecular biology (relatives share DNA).
  5. Hardy-Weinberg equilibrium occurs when genetic distribution remains constant in large, isolated, randomly mating populations with no mutation and no natural selection. These conditions rarely (if ever) occur together.

Key Topics–Evolution

Remember that the AP Biology exam tests you on the depth of your knowledge, not just your ability to recall facts. While we have provided brief definitions here, you will need to know these terms in even more depth for the AP Biology exam.

Types of Evolutionary Change

  • Natural selection: Process by which organisms best adapted to their environment survive to pass their genes on through offspring; idea pioneered by Charles Darwin
  • Sexual selection: Selection driven by the competition for mates, in relation to natural selection
  • Selective disadvantages: Characteristics that are bad for survival and/or mating
  • Selective advantages: Characteristics that are good for survival and/or mating
  • Genetic drift: Random evolutionary changes in the genetic makeup of a (usually small) population
  • Gene flow: The process of moving genes between populations as a result of the movement of individual organisms
  • Biological species concept (BSC): Definition of a species as a naturally interbreeding population of organisms that produce viable, fertile offspring
  • Prezygotic barriers: Mechanisms that prevent the formation of a zygote, leading to reproductive isolation
  • Isolation: The separation of some members of a population from the rest of their species; prevents interbreeding and may lead to the development of a new species
  • Postzygotic barriers: Mechanisms that prevent the development of a zygote into a fertile adult offspring
  • Hybrid: An offspring that is heterozygous for one or more gene pairs
  • Geographic isolation: Isolation due to geographic factors (e.g., islands are geographically isolated)
  • Allopatric speciation: Evolution of species that occurs in separate geographic areas
  • Geographic barrier: Any physical feature that prevents the ecological niches of different organisms (not necessarily different species) from overlapping
  • Sympatric speciation: Any physical feature that prevents the ecological niches of different organisms (not necessarily different species) from overlapping
  • Parapatric speciation: Occurs when limited interbreeding and negligible genetic exchange takes place between two populations
  • Extinction: The termination of an organism or species
  • Adaptive radiation: The production of a number of different species from a single ancestral species

Click the button to the right for our full Evolution notes!