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An incest taboo is any cultural rule or norm that prohibits acts of sexual relations between relatives. Many cultures allow sexual and marital relations between aunts/uncles and nephews/nieces. In some instances, brother-sister marriages have been practiced by the elites with some regularity. This poses the question of the origin of the incest taboo as a universal characteristic of culture, and the question has often been framed as a question of whether it is based in nature or nurture. Parent-child and sibling-sibling unions are almost universally forbidden. One line of explanation sees the incest taboo as a cultural implementation of a biologically evolved preference for sexual partners with whom one is unlikely to share genes, since inbreeding may have detrimental outcomes. Another school argues that the incest prohibition is a cultural construct which arises as a side effect of a general human preference for group exogamy, which arises because intermarriage between groups construct valuable alliances that improve the ability for both groups to thrive. According to this view the incest taboo is not necessarily a universal, but is likely to arise and become more strict under cultural circumstances that favour exogamy over endogamy, and likely to become more lax under circumstances that favor endogamy. An explanation for the taboo is that it is due to an instinctual, inborn aversion that would lower the adverse genetic effects of inbreeding such as a higher incidence of congenital birth defects (see article Inbreeding depression). Since the rise of modern genetics, belief in this theory has grown. Some[clarification needed anthropologists reject this explanation. The increase in frequency of birth defects often attributed to inbreeding results directly from an increase in the frequency of homozygous alleles inherited by the offspring of inbred couples. This leads to an increase in homozygous allele frequency within a population, and results in diverging effects. Should a child inherit the version of homozygous alleles responsible for a birth defect from its parents, the birth defect will be expressed; on the other hand, should the child inherit the version of homozygous alleles not responsible for a birth defect, it would actually decrease the ratio of the allele version responsible for the birth defect in that population. The Westermarck effect, first proposed by Edvard Westermarck in 1891, is the theory that children reared together, regardless of biological relationship, form a sentimental attachment that is by its nature non-erotic. Melford Spiro argued that his observations that unrelated children reared together on Israeli Kibbutzim nevertheless avoided one another as sexual partners confirmed the Westermarck effect. Joseph Shepher in a study examined the second generation in a kibbutz and found no marriages and no sexual activity between the adolescents in the same peer group. This was not enforced but voluntary. Looking at the second generation adults in all kibbutzim, out of a total of 2769 marriages none were between those of the same peer group. However, according to a book review by John Hartung of a book by Shepher, out of 2516 marriages documented in Israel, 200 were between couples reared in the same kibbutz. These marriages occurred after young adults reared on kibbutzim had served in the military and encountered tens of thousands of other potential mates, and 200 marriages is higher than what would be expected by chance. Of these 200 marriages,however, only five were between men and women who had been reared together for the first six years of their lives, which might argue against the Westermarck effect. A study in Taiwan of marriages where the future bride is adopted in the groom's family as an infant or small child found that these marriages have higher infidelity and divorce and lower fertility than ordinary marriages. A result which was argued to be consistent with the Westermarck effect. One objection against an instinctive and genetic basis for the incest taboo is that incest does occur. Anthropologists have documented a great number of societies where marriages between some first cousins are prohibited as incestuous, while marriages between other first cousins are encouraged. Therefore, the prohibition against incestuous relations in most societies is argued not based on or motivated by concerns over biological closeness. Other studies on cousin marriages have found support for a biological basis for the , current supporters of genetic influences on behavior do not argue that genes determine behavior absolutely but that genes may create predispositions that are affected in various ways by the environment including culture. #incest #exogamy #endogamy #cousinRelations #taboo #gene #geneExpression #GeneticsLecture #WestermarckEffect #inbreeding #Cancer #GeneticExamQuestionsSolutions #sexualRelations #geneticCode #chromosome #GeneticsExamQuestionsSolutions #genotype #gen
