‘Researchers who wanted to find out why it is not only taboo to kiss your sister, but also disgusting, said on Wednesday they have discovered why in a discovery that challenges some basic tenets of Freudian theory.
The instinct evolved naturally and cannot be taught, John Tooby and Leda Cosmides of the University of California Santa Barbara wrote in their report in the journal Nature. [..]
“This data shows that the degree to which we feel those things is governed by these cues that, for hunter-gatherers, predict whether somebody is a sibling. And it works regardless of your beliefs — who you are told who your siblings are,” she said.’