Sunday, February 2, 2014

Oxytocin, monogamy and altruistic punishment

Prairie voles with their litter
Let me introduce you to the prairie vole, a small mammal that has attracted considerable attention in scientific circles for the last decade or so. Prairie voles are rodents with short tails and small ears, and are found in North America from west of the Rockies to east of Appalachia. What is so notorious about prairie voles is that they are strictly monogamous: a male and a female form a bond for life. However, a very close cousin of the prairie vole, the montane vole, is not monogamous at all. In view of that, some scientists decided to find out how the brain of the prairie vole is different from that of the montane vole. They found that female prairie voles have more oxytocin and oxytocin receptors in the nucleus accumbens and the amygdala, which are areas of the brain important in emotions and decision-making. Oxytocin was first recognized as the peptide that induces uterine contractions during labor. More recently, it has been shown to be crucial for many forms of social bonding. For example, it goes up in the blood when a dog is being petted, in both the dog and the human! Back to our friends the voles, scientists went on to genetically modify the montane voles by increasing the production of oxytocin in the brain. And, voila! these montane voles turned out to be as monogamous as their cousins the prairie voles. What about the male voles? Well, in them monogamous behavior seems to be determined by another peptide, vasopressin, which is nevertheless quite similar to oxytocin.

Oxytocin also attracted the attention of researchers of a totally unrelated field: economics. Some unconventional economists decided to put to the test the basic belief of capitalism that market decisions are rational. They found that they are not. Human transactions are based more on trust and empathy that on cold-blooded decisions on what is to lose and what is to gain. For example, people in all cultures engage in something called altruistic punishment: they will go at great length to punish individuals that they perceive as being unfair and untrustworthy. One way they determined this is with an experiment called the “ultimatum game”. In it there are two players. Player one is given a sum of money, say $10, of which he has to offer a certain amount to player 2. If player 2 takes the offer, both get to keep the agreed amount of money. However, if player 2 rejects to offer, both of them lose the money. The results of the ultimatum game are consistent between people of all sexes, religions and cultures: below a certain amount (about $3-4 if the total amount is $10), player 2 decides that player 1 is not treating him fairly and rejects the offer. That means that he is willing to lose 2, 3 or even 4 bucks to punish player 1 for being greedy, that’s why is called “altruistic punishment”. Oxytocin comes into play because when their levels of oxytocin were increased players were more generous in their monetary offers. Testosterone did the opposite. In fact, men are more inclined to altruistic punishment than women.

Oxytocin and vasopressin are now called the “social hormones” because they strongly influence social behaviors like bonding, trust and empathy. However, we should not fall into the simplistic belief that oxytocin makes us good. It has been observed that this neuropeptide is involved in some nasty human behaviors, like xenophobia and intolerance. This is because oxytocin increases both bonding with the members of our group and exclusion of anybody perceived as a stranger. If you think about it, monogamy entails both feeling close to our spouse and rejecting member of the opposite sex that are not our spouse: bonding and exclusion. On the other hand, the role of vasopressin in monogamy in males seems to have more to do with possessiveness and territoriality than with emotional bonding - the male perceives the female as part of his territory and defends her as such. Likewise, altruistic punishment has a good side -like pursuing criminals-, and a bad side -like road rage and other conflicts that get started when we think that somebody is taking advantage of us.