Selection

Both natural and artificial selection occur in human beings. If a trait is lethal and kills before reproductive maturity, then that gene mutation is gradually depleted from the population. Mutations with milder effects persist longer and are more common than very severe mutations, and recessive mutations persist for much longer than dominant ones. With a recessive trait, such as albinism, the parents are usually both carriers of a single copy of the gene and may not know that they carry it. If a child receives a copy of this gene from both of the carrier parents, the albino child may die young, may find it difficult to find a partner, or may end up marrying much later in life. This is usually considered a form of natural selection.

Considerable abuse of genetic knowledge in the first half of the twentieth century led to the eugenics movement. Advocates of eugenics claimed some people were more fit and others less fit (or unfit), and argued that the least fit should be persuaded or forced not to reproduce. Eugenicists typically defined as unfit those who were "feeble-minded, criminal, socially deviant, or otherwise undesirable." Coerced sterilization, a form of artificial selection, was practiced on some of these individuals.

SEE ALSO CLONING GENES; EUGENICS; HARDY-WEINBURG EQUILIBRIUM; MULLER, HERMANN; MUTAGENESIS; MUTATION.