Common sense would have us tell that remaining faithful to one’s partner (i.e. monogamy) is a decision based on moral character, right?
Common sense would have us tell that if you commit an act of adultery, you are to blame, right?
But this leads to the question of what constitutes “character” in the first place. Could this too be guided by mechanisms below the radar of consciousness?
Let’s consider the prairie vole. This is a creature that lives in underground burrows. However, unlike other voles and other mammals, prairie voles remain monogamous. They are supremely faithful to their partner. How wonderful and caring and an example to all adulterers! Prairie voles form life long pair-bonds in which they nest together, huddle up, groom and raise their baby voles as a team. Aaaaww how sweet.
But why do they exhibit such faithful behaviour when their very close cousins are more wanton and liable to sleep around?
The answer = vasopressin
When a male vole repeatedly has sex with a female vole, a hormone called vasopressin is released into his brain. The vasopressin binds to receptors in a part of the brain called the nucleus accumbens, and this binding initiates a pleasurable feeling that becomes associated with the female. So whenever he has sex with the female vole, vasopressin is released, he feels supremely good and happy – and this locks in monogamy. Why should he sleep around when there is pleasure to be had from this one, and only one, female. Thus this is pair-bonding. If you block vasopressin the pair-bonding goes away. Amazingly, biochemists can use genetics to convert monogamous prairie voles to polygamous voles.
Does vasopressin matter for human relationships?
In 2008, a team of scientists in Sweden examined the gene for the vasopressin receptor in 552 men in long-term heterosexual relationships. The researchers found that a section of the vasopressin receptor gene can come in variable numbers: a man might carry no copies of this section, one copy, or two copies. The MORE the number of copies of this section of the gene, the WEAKER the effects of vasopressin in the brain. The results were surprising in their simplicity.
Men with more copies of the segment of the gene scored worse for measures of pair bonding. Men with fewer copies of the section of the gene scored higher. Basically, men with fewer copies of the segment of the gene had fewer perceived marital problems, had stronger relationships, and the quality of their marital life was rated as higher by both spouses. Those with two copies of the gene segment were more likely to be unmarried and single, and if they were married, they were more likely to have marital problems.
This does not mean that choices and environment and a whole host of other factors don’t matter. They do – but some men come into the world with a genetic disposition that makes it easier for them to hold a single partner.
Women – if you’re reading this, maybe its a good idea to demand genetic tests of your boyfriends before you decide to say ‘yes’ to their marriage proposal…
Now moving onto divorce!
Evolutionary psychologists have been studying couples (as they do!) and lo and behold they have discovered that when people fall in love, there’s a period of up to three years during which the zeal and fire and infatuation and passion ride at a peak. During those 3 years life is great and your girlfriend (or wife) is the best thing ever! The internal signals in the body and brain are literally a love drug. And then the vasopressin begins to decline. We are programmed (it seams) to lose interest in a sexual partner after the time required to raise a child has passed – typically on average about 4 years!
Foxes do the same. They pair-bond for breeding season, stick around just long enough to raise their offspring to a certain age, and then split. By researching divorce in sixty countries (across religious and cultural and economic boundaries) researchers have found, that in almost all countries, divorce peaks at about 4 years into marriage. Basically, vasopressin (the love drug) sticks around at elevated levels for about 4 years, before levels decline, leading to marital upheaval and moaning insufferable partners!
So next time you get accused of adultery, next time you are unfaithful to your spouse, next time you have a big argument with your spouse over the remote control or the toilet seat – remember, it’s not your fault. It’s the vasopressin!