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 (1891) 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 (collective farms), 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 life revealed 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
Sigmund Freud argued that as children, members of the same family naturally lust for one another (see Oedipus complex), 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.
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 substantial attraction 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.
- Inbreeding, Incest, and the Incest Taboo: The State of Knowledge at the Turn of the Century, Arthur P. Wolf and William H. Durham (Editors), Stanford University Press, 2004, ISBN 978-0804751414. Introduction
- Shepher, Joseph (1983). Incest: A Biosocial View. Studies in anthropology. New York: Academic Press. ISBN 0-12-639460-1. LCCN 81006552.
- Freud, S. (1913). Totem and Taboo in The Standard Edition of the Complete Psychological works of Sigmund Freud, Vol. XIII.
- Shor, Eran; Simchai, Dalit (2009). "Incest Avoidance, the Incest Taboo, and Social Cohesion: Revisiting Westermarck and the Case of the Israeli Kibbutzim". American Journal of Sociology. 114 (6): 1803–1842. doi:10.1086/597178. PMID 19852254.
- Scheidel, Walter. "Evolutionary psychology and the historian." The American Historical Review 119, no. 5 (2014): 1563-1575.
- Bering, Jesse (17 Aug 2010). "Oedipus Complex 2.0: Like it or not, parents shape their children's sexual preferences". Scientific American. Retrieved 18 September 2014.
- Paul, Robert A. (1988). "Psychoanalysis and the Propinquity Theory of Incest Avoidance". The Journal of Psychohistory 3 (Vol. 15), 255–261.
- Spain, David H. (1987). "The Westermarck–Freud Incest-Theory Debate: An Evaluation and Reformation". Current Anthropology 5 (Vol. 28), 623–635, 643–645.
- Westermarck, Edvard A. (1921). The history of human marriage, 5th ed. London: Macmillan.
- Lieberman, D., Tooby, J., & Cosmides, L. (2007). "The architecture of human kin detection", Nature, 445, 727–731.