Let's try a different tack.

Scientists have linked the hormone Oxytocin (http://en.wikipedia.org/wiki/Oxytocin) to the feeling of 'bonding' that men and women feel immediately after sex, as well as in breast feeding, labour, etc etc.

[It's worth noting that the presence of Oxytocin in men during/around orgasm occurred in a proportion of the sample that was not of statistical significance.]

Perhaps asking men and women whether or not there is a social/hormonal/whatever bond that occurs during and after sex might yield different answers. Males, according to this research, aren't as needy/clingy/etc.