The Westermarck effect, also known as reverse sexual imprinting, is a psychological hypothesis that people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction. This hypothesis was first proposed by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage as one explanation for the incest taboo. The existence of the Westermarck effect has achieved some empirical support. Observations interpreted as evidence for the Westermarck effect have since been made in many places and cultures, including in the Israeli kibbutz system, and the Chinese Shim-pua marriage customs, as well as in biologically-related families. In the case of the Israeli kibbutzim, children were reared somewhat communally in peer groups, based on age, not biological relations. A study of the marriage patterns of these children later in liferevealed that out of the nearly 3,000 marriages that occurred across the kibbutz system, only 14 were between children from the same peer group. Of those 14, none had been reared together during the first six years of life. This result suggests that the Westermarck effect operates during the period from birth to the age of six. When proximity during this critical period does not occur—for example, where a brother and sister are brought up separately, never meeting one another—they may find one another highly sexually attractive when they meet as adults or adolescents, according to the hypothesis of genetic sexual attraction. This supports the theory that the populations that appear to exhibit the hypothetical Westermarck effect became predominant because of the deleterious effects of inbreeding on those that did not.
Contrasting Westermarck and Freud
argued that as children, members of the same family naturally lust for one another, making it necessary for societies to create incest taboos, but Westermarck argued the reverse, that the taboos themselves arise naturally as products of innate attitudes.
Criticism
Some sociologists and anthropologists have criticized the validity of research presented in support of the Westermarck effect and the contention that it serves as an ultimate demonstration for the viability of natural selection theory in explaining human behaviour. For example, a 2009 study by Eran Shor and Dalit Simchai demonstrated that although most peers who grew up closely together in the Israeli kibbutzim did not marry one another, they did report substantialattraction to co-reared peers. The authors conclude that the case of the kibbutzim actually provides little support for the Westermarck effect and that childhood proximity cannot in itself produce sexual avoidance without the existence of social pressures and norms. However, Austrian historian Walter Scheidel argues that recent research has raised some support for Westermarck's hypothesis, arguing that studies show that cousin-marriage in Lebanon has a lower success rate if the cousins were raised in sibling-like conditions, first-cousin unions being more successful in Pakistan if there was a substantial age difference, as well as reduced marital appeal for cousins who grew up sleeping in the same room in Morocco. Evidence also indicates that siblings separated for extended periods of time since childhood were more likely to report having engaged in sexual activity with one another. American psychologist Jesse Bering cites several studies that seem to contradict the standard view of the Westermarck effect as an innate learning process; instead, it may be a cultural phenomenon. People seem to have sexual preferences toward faces that resemble their parents' or their own. If correct, this would suggest that Freud's idea of the Oedipus complex had some merit to it.
