Remember when you were unattached and fancy free? It may never have happened. If you envy your single friends for all of the no-strings, fun sex they’re having, don’t bother. It’s not all as mindlessly meaningless as it seems, according to biological anthropologist Helen Fisher, PhD.

Fisher explains how there’s enough dopamine triggered by sexual activity to actually make a person fall in love with their partner. And, she points out, with an orgasm comes a rush of oxytocin and vasaprezin, brain chemicals associated with deep emotional attachment. So people just happen to fall in love from casual sex?

Maybe not. The data on why hookups happen is intriguing. Fisher cites a study done by Fisher’s colleague Justin Garcia in which a surprisingly large percentage of male and female respondents — about half of them — report that they’d participated in one-night stands with hopes of waking up in a long-term relationship, and many actually did.

On the edge of the bed and love

Garcia’s subsequent studies have found much the same, though the gender percentages shift from study to study, mostly with higher percentages of women looking for a permanent partner. Regardless, lots of people in seemingly mindless hookups are actually looking for more, at least unconsciously.

Also interesting is another study of Garcia’s that suggests there may be a genetic reason some people are more inclined toward promiscuity (and infidelity). Men and women in the study who had a certain variation of DRD4, which is involved in dopamine sensitivity, reported a higher number of one-night stands.