Incest is the infraction of the taboo upon sexual relations between any two members of the nuclear family except husband and wife, that is, between parents and children or any sibling pair. The taboo may be extended to include other specific relatives or categories of kin, whose relationship ties may be biological, affinal, classificatory, or fictive, and sexual relations between any two individuals so defined will be treated as incest. “Taboo” is a more appropriate term than “prohibition,” for the incest interdiction, which often lacks any legal sanction, is typically accompanied by a special sense of intense horror. In its most stringent applications the taboo may preclude any overt expression of intimacy by, or interaction between, those affected by the interdiction. Although the incest taboo in some form occurs in every known society, there is great variation among societies not only with regard to the extensiveness of its application and the range of intensity of associated emotions but also in the occurrence of ceremonial and customary abrogations and in the relative frequency of specific types of infraction.
It is agreed that two adults who with consent of one another can have sex with each other but it does not cover the fact that having sexual relationship with a close relative can turn out to have grave consequences. When a person mates with a partner of completely different genes, the chance of passing on recessive genes is only 50%. Many times the genes remain dormant but when a person mates with a partner with common genes, the chance of passing on conditions known as autosomal recessive disorders which is conditions that are inherited through recessive genes, including cystic fibrosis, sickle cell anemia, and albinism—increases significantly.
Some other effects can be increased risk of infertility, birth defects like cleft palates, heart conditions, facial asymmetry, low birth weight, slow growth rate, and neonatal mortality. 40 percent of children whose parents were first-degree relatives were born with autosomal recessive disorders, congenital physical malformations, or severe intellectual deficits were found out in a study. As per the study, when first-degree relatives get into sexual relationship, the risk of their offspring suffering from an early death, serious birth defect, or mental disability increases to almost 50 percent.