The taboo of incest has been discussed by many social scientists. Anthropologists attest that it exists in most cultures. As inbreeding within the first generation often produces expression of recessive traits, the prohibition has been discussed as a possible functional response to the requirement of culling those born deformed, or with undesirable traits. Some biologists like Charles Davenport advocated traditional forms of assortative breeding, i.e., eugenics, to form better "human stock".
In discussing humans, the term inbreeding is often considered highly offensive and judgmental. However, such marriages are not illegal in most of the world. Although it is an undisputed fact that cousin marriages increase the probability of genetic disease, the level of statistical increase varies with the degree of relationship, and the frequency of the marriages. The casual use of the term inbred implies that some degree of degradation exists, when in fact there may be no effect at all.
Some Hindus follow the Gotra system, which prescribes prohibition of marriages among relatives based on a name attached to paternal relatives, to prevent inbreeding. Direct inbreeding is also prohibited in Islam, as described in the Quran (chapter 4, verse 23).