Research has indicated that people tend to develop an attraction towards others who resemble their kin or themselves.
In a series of experiments where subjects viewed photographs of their opposite-sex parent or a photo morphed with their own face, researchers found that people are turned on by photographs of people who resemble their close genetic counterparts.
"People appear to be drawn to others who resemble their kin or themselves," ABC News quoted psychologist R. Chris Fraley of the University of Illinois, lead author of the study, as saying.
The debate about whether aversions against incest stem from a cultural adaptation to suppress biological urge or a psychological adaptation that evolved by natural selection dates back to the early 1900s.
Psychoanalyst Sigmund Freud proposed the former explanation, and sociologist Edward Westermarck proposed the latter, arguing that there is a critical period while people are growing up during which if they are raised with someone they won't find them attractive.
While contemporary scholars have concluded that Westermarck was right, and Freud was wrong, but in the new study, Fraley argued that the debate may have been settled prematurely.
"There is evidence on both sides now. There is some reason to think that there is something to Westermarck, that there is a critical period, but it may also be that we find and trust and align ourselves with people who have more common alleles," said psychologist David Schmitt from Bradley University.
The experiments support the Freudian idea that we have subconscious mechanisms that make us attracted to features that remind us of our own, and that cultural taboos against incest exist to override that primitive drive.
However, one possible explanation for the results of the study is simply that people's brains tend to process familiar images more easily.
The study has been published in Personality and Social Psychology Bulletin.