Freud was right: we are attracted to our relatives

Freud said there'd be no need for incest to be such a powerful cultural taboo if people weren't sexually attracted to their relatives in the first place. Given that in-breeding is associated with increased mortality, he argued that the incest taboo had emerged as way to keep our dangerous incestuous desires in check. Evolutionary psychologists take a strikingly different view. Inspired by Edward Westermarck, the Finnish sociologist and anthropologist, they argue that we've evolved automatic psychological processes that lead us to find our relatives sexually aversive, not attractive, thus decreasing the likelihood of in-breeding occurring. Who's right - Freud or Westermarck?

Chris Fraley and Michael Marks asked 74 students to rate the sexual attractiveness of 100 strangers' faces. Crucially, for half the students, each face was preceded by a subliminal presentation of a family member. For the remaining control students, the subliminal presentation was of someone else's family member, i.e. a non-relative.

Westmarckian theory predicts that the non-conscious presentation of a relative will trigger the automatic system that makes relatives seem sexually unattractive, with the knock-on effect that the strangers' faces would be rated as less attractive. Contrary to this prediction, the students who were subliminally presented with a family member actually rated the strangers' faces as more attractive than did the control students.

In a second study, 40 students rated the sexual attractiveness of faces that either had or hadn't been morphed to varying degrees to resemble their own face (a way of simulating genetic relatedness). The students presented with the morphed faces rated them as more sexually attractive than did control students who viewed unaltered faces, and the greater the morphing, the greater the perceived attractiveness. This appears to be consistent with Freud's claim that we really are attracted to our relatives, and it also chimes with past research showing that we tend to marry people who look similar to ourselves - a phenomenon known as homogamy.

For the final study, a group of students once again rated the sexual attractiveness of strangers' faces. This time half the students were told falsely that some of the faces had been morphed to resemble them, as a way to simulate genetic relatedness. The students fed this lie subsequently rated the faces as less attractive than the control students who thought they were simply rating strangers' faces. The finding appears to support Freud's contention that it is the incest taboo that causes us to find people who we think we're related to, less attractive.

Fraley and Marks say their findings are largely in keeping with Freud's writings, whilst being at odds with Westermarckian evolutionary psychology. However, whereas Freud referred to unconscious desires, Fraley and Marks think our attraction to our relatives could be triggered by a kind of human sexual imprinting, according to which our sexual preferences are shaped by our early experiences, or by mere familiarity, or both. The point about familiarity refers to a well established finding in psychology that we tend to find things that are more familiar more appealing.

The influences of imprinting and familiarity are balanced out, Fraley and Marks suggest, by the cultural deterrent of the incest taboo and also by habituation - the tendency for excessive familiarity to breed indifference or contempt. Indeed, the deterring influence of taboo and habituation could explain the finding that people are less likely to mate with a person with whom they are reared, even if that person is unrelated (this is known as the Westermarck effect).

Fraley and Marks call their approach to this topic the evolutionary psychodynamic perspective. 'From this point of view,' the researchers said, 'one reason Oedipus longed for (and eventually married) his mother in the myth of Oedipus Rex is because she was related to him. His desire was possible, however, only because he was unaware of his true relationship to her.'
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Fraley RC, & Marks MJ (2010). Westermarck, freud, and the incest taboo: does familial resemblance activate sexual attraction? Personality and social psychology bulletin, 36 (9), 1202-12 PMID: 20647594