It’s no secret that the media have a tendency to hype studies of individual genes, exaggerating the potential behavioral or health impacts. Genetic testing services such as 23 and Me have also been accused of contributing to this problem. It’s particularly tempting to do this when a recently published study isolates a clear genetic marker for a certain trait.
Case in point is a recent piece by Richard A. Friedman in the New York Times Sunday Review, titled Infidelity Lurks in your Genes. The spark for the article was a study of Finnish twins and siblings showing that women with certain variants of AVPR1A–a gene for a hormone called arginine vasopressin (AVP) or antidiuretic hormone (ADH)–have an elevated incidence of ‘extra pair bonding’, which is to say sleeping around.
The study, which is not even new–it had been released last fall–enjoyed a lot of press and Friedman’s piece was very popular, because–let’s face it–the title was brilliant and the highlighted study produced impressive results, published in the prestigious journal Evolution and Human Behavior. The study focused on 7400 Finnish twins and their siblings who had been in a relationship for at least a year.
[The researchers] found that 9.8 percent of men and 6.4 percent of women reported that they had two or more sexual partners in the previous year. His study, published last year in Evolution and Human Behavior, found a significant association between five different variants of the vasopressin gene and infidelity in women only and no relationship between the oxytocin genes and sexual behavior for either sex. That was impressive: Forty percent of the variation in promiscuous behavior in women could be attributed to genes.
Data in animals confirm that these two hormones are significant players when it comes to sexual behavior. An intriguing clue came from the pioneering work of Dr. Thomas R. Insel, now the director of the National Institute of Mental Health, who studied the effects of vasopressin and oxytocin in a little rodent called the vole. It turns out that there are two closely related species of voles: montane voles, which are sexually promiscuous, and prairie voles, which are sexually monogamous and raise their extended families in burrows.
“Our research clearly shows that people’s genetic make-up influences how likely they are to have sex with someone outside their main partnership, said Dr Brendan Zietsch, research fellow at the university’s school of psychology, who led the study. “Isolating specific genes is more difficult because thousands of genes influence any behavior and the effect of any individual gene is tiny. But we did find tentative evidence for a specific gene influencing infidelity in women. More research will be needed to confirm this finding.’’
Sleeping around depends on numerous, non-hereditary factors
But before you start asking your lawyer whether testing positive for any of the implicated vasopressin gene variants might get you a better deal in your divorce, consider that the implications of the study are doubtful for a bunch of reasons, some of which Friedman, a professor of clinical psychiatry at Weill Cornell Medical College, pointed out himself. Friedman advised caution caution on the following grounds:
As Dr. Zietsch points out, there are so many other factors that are necessary for promiscuous encounters, like circumstance and the availability of a willing and able partner. Although this is the largest and best study on this, it’s not clear why there was no relationship between the vasopressin gene and promiscuous behavior in men.
Friedman later explained that the study should not be interpreted to mean that possessing an infidelity gene variant of AVPR1A should give anyone a reasonable excuse for engaging secretly in “extra pair bonding”. And so, despite the winning headline, the actual message is that all of the various social factors dominate, even if there is some real genetic contribution to the behavior.
There are also some potential problems with the study. One problem appears if one scrolls through the study to the methods section, which explains how the sexual behavior data were acquired: the subjects were asked. Basically, they had to report on their relationships and their number of sexual encounters and sexual partners in and out of marriage. In behavioral studies, self-reporting is often not reliable, particularly with a sensitive topic.
Furthermore, as science writer John Horgan pointed on in reviewing the issue on the Scientific American blog, the study authors themselves cited previous studies showing no connection between extra pair bonding and the AVPR1A gene. So the entire issue is plagued with contradictions. That may be reason for further investigation, but as for making the AVPR1A gene the focus of a swarm of news stories, that may have been a little premature.
David Warmflash is an astrobiologist, physician and science writer. Follow @CosmicEvolution to read what he is saying on Twitter.