[itchyjunk]

First off, this is too vague of a generalization based on their sample size. It makes for a nice casual read but I can't take it too seriously. Though, I must note, my anecdotal experience also makes me think this is more of a norm.

This also agrees with observed primate behaviors. Males have an incentive to identify potential mates while female have incentive to pick one out of the many available. (Male can impregnate many females in a year, female can only bear one child at a time.)

Friendship and romance also have overlapping characteristics. Example: "bromance" where it's not sexual but outsiders might see characters typically associated with romance.

It's too big of a topic and I would probably write an essay.