It's not an excuse, but there may be a biological reason that jail-bound Aimee Sword was sexually attracted to the teenage son she gave up for adoption.
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," said psychologist R. Chris Fraley of the University of Illinois, lead author of the study published July 20 in Personality and Social Psychology Bulletin. "It is possible, therefore, as Freud suggested, that incest taboos exist to counter this primitive tendency."
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.
In recent years, Fraley says, contemporary scholars have concluded that Westermarck was right, and Freud was wrong. But based on his study, Fraley argues that the debate may have been settled prematurely.
"There is evidence on both sides now," said psychologist David Schmitt from Bradley University. "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."
In the first experiment, people were shown a series of faces of strangers and asked to rank their sexual attractiveness.
Before each of the faces were shown, half the subjects were subliminally exposed to photographs of their opposite-sex parent, by flashing the images so quickly that they couldn't be processed consciously. The other half of the participants was shown photos of unrelated parents.
People who were primed with images of their own mom or dad were more likely to find the faces in the subsequent photo attractive than did people primed with a random image.
In the second experiment, participants were asked to rank the sexual attractiveness of another set of faces, but this time the faces were morphed to be composites of two different faces.
Unaware that their own faces were part of the morph, half of the subjects were shown faces that were up to 45 percent their own, like an artificial sibling. The other half were shown morphs of faces that were not their own.
The people who saw faces morphed with their own found the images more sexually appealing.
In the third experiment, people were shown morphs that didn't involve their own faces, but half were led to believe the morphs did contain their own faces.
In this case, the people who wrongly believed the morphs contained their own face ranked those pictures as less attractive.
All three 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. Fraley says a subsequent study where the faces to be ranked range in familiarity and the point in life where they were known (early childhood, elementary school) is needed to tell if this is the case.