While the influence of oxytocin on human bonding remains speculative, there is mounting scientific evidence that it does play a central role.

In animal studies, oxytocin and its close cousin, vasopressin, influence pair bonding, social monogamy and parental behaviours. Human brain and hormonal physiology are very similar to that of other monogamous mammals.

Moreover, studies of humans have found that sniffing oxytocin increases trust, and that oxytocin levels rise when a mate offers comfort or support.

So, Dr. Keroack’s theories of human bonding are likely correct.

However, there is no evidence that extramarital sex causes people to build up a tolerance to the bonding effects of oxytocin.

The bond with a mate, a child and a friend seems to activate the same brain systems, according to fMRI studies. A mother can love her husband and several children, and her interactions with them seem to reinforce that bond, not diminish it.

I do agree with you that the divorce rate in the first years of marriage could be due to problems with bonding. But I think it’s more likely that generations are growing up without the kind of parenting that teaches the hormonal responses that will make them able to form bonds with adults later.