I think "friendships" are further removed from base evolutionary instincts than sexual relationships are. Your base evolutionary instinct to select for mates is

I think "friendships" are further removed from base evolutionary instincts than sexual relationships are. Your base evolutionary instinct to select for mates is different than the ones we developed to form societies. To put it bluntly, the colloquial prevalence of "thinking with your [genitals]" certainly indicates that people's higher social brain function tends to be clouded more often (reverting to base instinct) when sex is involved. (Obviously, good relationships are based on friendship as well, but by definition the relationships in this study were not successful ones.)