Love, Trust, and Sexual Infidelity

Research on how oxytocin affects our social and sexual behavior.

Posted Dec 09, 2017

Ed Gregory/Pexels
Source: Ed Gregory/Pexels

Oxytocin is a neurotransmitter (hormone) released by breastfeeding women and the infants whom they are nursing. Studies conducted on primates reveal that it is responsible for the bond formed between mother and child immediately after birth, before they have managed to forge a deeper connection. The hormone is also released by both sexes during sexual orgasm and is therefore often called the “love hormone.” Oxytocin is a wonderful evolutionary mechanism that increases the chances that a newborn infant will survive, thus passing on genes from one generation to the next.

Before we have children of our own, many of us marvel at the ability of new mothers to find the energy resources needed to care for a newborn infant after nine exhausting months of pregnancy. They manage to do this within seconds of what is often a difficult and draining childbirth experience, without having had any opportunity to form an emotional bond with their child. This is accomplished partly because the evolutionary development of primates, including humans, has supplied females with a hormone that makes bonding between mother and child completely instinctive. It even enables an infant to understand the importance of finding his mother’s breasts minutes after emerging into the world; infants are born with the instinct to suckle their mother’s milk.

Given the important role oxytocin plays in creating bonds between mothers and infants, it is reasonable to suppose that it also influences other aspects of social behavior in healthy adults. Researchers in Zurich have shown, several years ago, that oxytocin can also induce trust.

Oxytocin is a benign hormone that is harmless when introduced into the body in small doses (this is usually accomplished by using nose drops, similar to the nose drops used to ease the symptoms of the common cold). The Zurich experimenters had two groups of subjects play the trust game (a simple game that requires a player to trust his/her counterpart to sustain a profitable cooperation.) One group received a dose of oxytocin before playing the game, while a control group was administered a placebo containing all the same elements except the active element. The results were surprising. Members of the group receiving doses of oxytocin achieved a much greater level of cooperation and earned more money. In a different research work published in Psychological Science, Einav Hart, Salomon Israel and I showed that oxytocin may also impair our cognitive ability to discover manipulations and ill intentions by others.

But the level of oxytocin in our blood is, probably, also responsible for our sexual fidelity (or the lack of it). This has been revealed by studying the behavior of voles, focusing on two different species of voles. The first one called meadow voles who are of a “love ’em and leave em” type. These voles move on to their next sexual partner as soon as the former one got pregnant. Meadow voles are also known to suffer from some sort of “sexual Alzheimer.” They simply keep no memory of their former sexual partner. In contrast, prairie voles are monogamous. They essentially mate with the same partner for life. They also share nest building and parental roles equally with their partners, and when their partner dies they show distinct signs of grief and depression. The main difference between these two types of vole lies primarily is one gene that controls the receptors of oxytocin and vasopressin in the brain. Among meadow voles this gene appears in a version that practically shuts down these receptors, whereas among prairie voles the gene keeps them on and ready to receive the neurotransmitters. In an amazing experiment at Emory university Larry Young and his team managed to turn playboy meadow voles into family-guy voles by manipulating the gene that controls these receptors. A one-time injection into the brain is all that needed to achieve this dramatic change in behavior. What Young’s experiment implies about us humans is still in the territory of science fiction. Does a stable relationship with our partner depends, to a large extent, on our and our partner’s genes? Shall we see in the near future a cure for sexual infidelity in the form of a one-time injection (some may raise the same question regarding a cure for sexual fidelity)? How can we find out whether we poses a genetic predisposition for sexual infidelity?