Selection

Artificial selection, which is even older than agriculture, refers to a conscious effort to use for future breeding those varieties of a plant or animal that are most useful, attractive, or interesting to the breeder. Artificial selection is responsible for creating the enormous number of breeds of domestic dogs, for instance, as well as high-yielding varieties of corn and other agricultural crops.

Selection also occurs in nature, but it is not conscious. Charles Darwin called this natural selection. Darwin saw that organisms constantly vary in a population from generation to generation. He proposed that some variations allow an organism to be better adapted to a given environment than others in the population, allowing them to live and reproduce while others are forced out of reproduction by death, sterility, or isolation. These genetic variations gradually replace the ones that fail to survive or to reproduce. This gradual adjustment of the genotype to the environment is called adaptation. Natural selection was not only Darwin's key mechanism of evolution for the origin of species, it is also the key mechanism today for understanding the evolutionary biology of organisms from viruses to humans. Natural selection leads to evolution, which is the change in gene frequencies in a population over time.

The concept of selection plays an increasingly important role in biological theory. New fields such as evolutionary psychology rely heavily on natural selection to explain the evolution of human behavioral traits, such as mate choice, aggression, and other types of social behavior. A great difficulty in such a theoretically based science is the paucity of experimental or direct evidence for presumed past environments and presumed behavioral responses that were genetically adaptive.