Evolution and natural selection review

Key terms

EvolutionThe process by which modern organisms have descended from ancient organisms over time
Common ancestorAn ancestor shared by two or more descendant species
Natural selectionEvolutionary mechanism in which individuals that are better suited to their environment survive and reproduce most successfully
VariationDifference between traits in individuals of the same species
AdaptationA trait that improves an organism's ability to survive and reproduce in an environment
FitnessThe ability of an organism to survive and reproduce
Artificial selectionSelective breeding of organisms to promote the appearance of desirable traits in offspring
Genetic driftA mechanism of evolution in which allele frequencies of a population change over generations due to chance

Darwin's theory of evolution

Charles Darwin developed a theory of evolution to explain the unity and diversity of life, based on the idea of shared common ancestors.

Natural selection

Darwin's theory was based on the mechanism of natural selection, which explains how populations can evolve in such a way that they become better suited to their environments over time.
Light colored mice are more easily seen by predators and are therefore preyed upon more. Dark mice are better adapted to their environment and better able to survive and reproduce.
Natural selection acting on mice population over time.
Individuals have variations within their heritable traits. Some variations make an individual better suited to survive and reproduce in their environment.
If this continues over generations, these favorable adaptations (the heritable features that aid survival and reproduction) will become more and more common in the population.
The population will not only evolve (change in its genetic makeup and inherited traits), but will evolve in such a way that it becomes adapted, or better-suited, to its environment.

Artificial selection

There are other types of selection, in addition to natural selection, that are out there in the world.
Artificial selection, also called "selective breeding”, is where humans select for desirable traits in agricultural products or animals, rather than leaving the species to evolve and change gradually without human interference, like in natural selection.
A timeline showing how dogs became domesticated over a long period of time due to artificial selection.
Dog breeding is a perfect example of how humans select for desirable or fashionable traits. Breeders deliberately mate parents with the hope of producing offspring with specific traits (such as color, size, ear shape, snout length, and so on).

Common mistakes and misconceptions

  • Evolution is not the same as adaptation or natural selection. Natural selection is a mechanism, or cause, of evolution. Adaptations are physical or behavioral traits that make an organism better suited to its environment.
  • Heritable variation comes from random mutations. Random mutations are the initial cause of new heritable traits. For example, a rabbit can't choose to have a different fur color. Rather, a genetic mutation causes a difference in fur color, which may help that rabbit hide better in its environment.
  • Natural selection acts on existing heritable variation. Natural selection needs some starting material, and that starting material is heritable variation. For natural selection to act on a feature, there must already be variation, and that variation must be able to be passed on to offspring.
  • Natural selection depends on the environment. Natural selection doesn't favor traits that are somehow inherently superior. Instead, it favors traits that are beneficial in a specific environment. Traits that are helpful in one environment might actually be harmful in another.