'The idea that boys want to sleep with their mothers strikes most men as the silliest thing they have ever heard. Obviously, it did not seem so to Freud, who wrote that as a boy he once had an erotic reaction to watching his mother dressing. But Freud had a wet-nurse, and may not have experienced the early intimacy that would have tipped off his perceptual system that Mrs. Freud was his mother. The Westermarck theory has out-Freuded Freud'.
—Steven Pinker, How the Mind Works

For those who haven't heard of this "Phew!" inducing theory, it counters Freud's well known argument that as children, members of the same family naturally lust for one another, making it necessary for societies to create incest taboos, but the Westermarck theory argues the reverse. The incest taboo arises as the product of innate attitudes that essentially exist in preventing inbreeding. 

Basically, children who are around people up to the age of 6 are desentized to later close sexual attraction to those people. Isn't this great!? I heard Freud's theory and have always felt uneasy wondering if just under the surface I'm really just wanting to clamp onto my mom's left boob or something. That going 'out for lunch' and 'window shopping' were thinly veiled slips of the tongue.