UCSB husband and wife research team John Tooby and Leda Cosmides know that if they were siblings, they wouldn’t be so hot for each other.

Tooby and Cosmides became particularly sure of this statement last week, when the pair published the results of their recent study about incestuous attraction in the weekly international science journal Nature. The results of the professors’ study demonstrate an evolutionary explanation for an individual’s sexual aversion to their siblings – contesting Sigmund Freud’s widely accepted theory that the incest taboo is simply a social phenomenon.

According to the Feb. 15 Nature article, the results of Tooby and Cosmides’ research reveal that the common lack of attraction between siblings is an evolutionary apparatus, composed of what the study calls “kin detection mechanisms.”

In particular, the researchers found two important detection mechanisms that are responsible for the feelings of disgust associated with the thought of engaging in incest with one’s siblings.

First, the study found that the time an individual spends during his childhood watching his mother care for another child contributes to a sexual aversion between the two children later in life. Secondly, the research revealed that the length of time these two individuals cohabitate with one another also has a significant impact on deterring sexual relationships between them in the future.

Therefore, the article said, incest aversion can even exist among unrelated persons, provided they had spent a substantial amount of time around one another during their earliest years. Unrelated children who have been raised together, then, by nature will still engage their kin detection mechanisms early on in life – precluding any future attraction between the two.

The results of the study are at odds with research on incest conducted by Freud, who argued in the late 19th century that attractions between family members occur naturally in all humans. The attractions, Freud said, are deterred and suppressed by society and the culture-based concept of incest taboo.

Tooby and Cosmides conducted the study by having participants complete a lengthy questionnaire about their attitudes towards siblings. In order to obscure the subject under study, the survey included a substantial number of questions unrelated to the topic of incest.

According to the article, the couple conducted the study because of a mutual interest in shedding light on incest, a topic that has not been the subject of much research within the scientific community. Tooby and Cosmides wanted to understand the reasons why kissing one’s own sibling is not only socially taboo, but is also either physically or mentally unpleasant, the article said.