Seminar Two
Evolution of sexuality
Molecules and pair bonding

“Ovulation can be hazardous to your judgment,” writes Sarah Blaffer Hrdy in her excellent book, Mother Nature: A History of Mothers, Infants, and Natural Selection. A woman may be more likely to be aroused or to fall in love with an actor in a film during the follicular phase of her cycle, when oxytocin levels are high, and may maintain the same strong response to seeing the actor in a film at a later time.

Oxytocin promotes affiliative feelings in humans, as it does in other mammals (oxytocin also induces uterine contractions and lactation). Hrdy reminds us that an awareness of our evolutionary heritage carries a warning to women “to keep an eye on their calendars.”

“Why do you think,” I was asked by an obstetrician-gynecologist friend, “that adolescent girls often get pregnant when they first have intercourse?” His answer, which enlightened and amazed me: ovulation coincides with the time of the month when a woman is “inebriated” with oxytocin. All else being equal, she is more likely to bond emotionally to a sexual partner and overcome sexual inhibitions at this time.

Oxytocin may lower inhibitions to approaching and trusting others. Oxytocin was administered as a nasal spray to nearly two-hundred college students playing an investment game with real money. The startling finding was that oxytocin, but not placebo, caused a large increase in trust and readiness to accept risks arising through interpersonal interactions.