Hormone study finds monkeys in long-term relationship look strangely human

by David Tenenbaum Monkeys in enduring relationships show a surprising correspondence in their levels of oxytocin, a key behavioral hormone, according to research published online June 28 in the journal Hormones and Behavior. While measuring oxytocin in the urine of 14 pairs of cotton-top tamarins, Charles Snowdon , a University of Wisconsin-Madison professor of psychology, observed a wide range of hormone levels. But he also saw a striking correspondence among the couples: When one mate had a high level of oxytocin, so did the other, and vice versa. Furthermore, partners with a high level of oxytocin performed correspondingly more cuddling, grooming and sex, while those with low levels of oxytocin spent less time on these relationship-building activities. The hormone oxytocin was originally studied for its role during childbirth, when it helps cement the mother-child emotional attachment. More recently, it has been linked to many other attachments. "Only in the past 20 years have we started to think more broadly about oxytocin's social function in forming and maintaining long-term relationships," says Snowdon.