Infidelity and number of sexual partners are both under moderate genetic influence and the correlation between these two traits is strong (47%). The resulting genetic correlation between the two traits was .47, so nearly half the genes impacting on infidelity also affect number of sexual partners.

First of all, here’s a link to the full Pdf.

Second of all, I’m highly skeptical about the validity of this study. Aside from the fatal exposure to sampling bias involved in studying a social taboo, it’s more-so the deliberate neglect of certain obviously valuable additional data points that raise the biggest red flags to me. Their entire approach seems geared towards arriving at a certain conclusion (which they can pat themselves on the back as having achieved) to produce a study that gets a lot of attention with a controversial summary, like the snippet used for this post here. Yes, clickbait exists in academia as much as in popsci as much as in tabloids. More attention drawn to your lab = more free exposure = more grant money to do further research.

An elementary understanding of genetics makes obvious the fact that if there’s a link to be had here, it’s not going to be a direct link. Rather, the link will involves a whole host of genetic variables (dozens or hundreds) that ultimately determine the relative probability that someone will commit adultery. Some of which are much more easily attained than others.

For starters, some easily attainable additional metrics could have included: A Big 5 personality evaluation; Evaluation of self esteem; questionnaire on childhood family life (“were your parents together or divorced? What was their relationship like? Was there known to be infidelity on behalf of either or both parents? How were you treated as a child?”); etc. These should all be of course analyzed for correlation with age of the twins respondent. Obviously, people change as they get older and younger respondents will presumably be more insecure, more freshly informed by adolescent experiences, etc.

Further, and this could be done also within a thoughtfully designed written questionnaire, would be an evaluation - in addition to self reported number of sexual partners (which, that obviously is going to be incredibly unreliable) - regarding the relative sexual interests / intensity of desire of each participant - aka ‘libido’. This would be harder for a participant to fudge completely the way they can the number of partners. I know there’s standardized psych evaluation tools out there for this. I’m talking questions like “how often do you think about sex? How much of a distraction is it? Ideally, if your partner was able and willing, how often would you like to have sex?” With questions like this, a respondent could try to sway their answers one way or another due to whatever mental hang ups they have going on, but they still wouldn’t know how the “average” person would be expected to respond. This way you could calculate a gradient of correlations across all respondents.

Lastly, for those that had had an affair and admitted to it, why not ask like “How long had you been together? We’re you generally satisfied by your partner? When in the relationship did this happen? How many times? We’re you shitfaced drunk one night a month after meeting the significant other and having a fight, or was your affair premeditated and carefully hidden for years?”

These things make a big difference. Obviously.

A little more challenging to do, but certainly worth the effort considering - well because when doing research the goal is learn something useful - would be to have blood samples submitted by each respondent to get a direct, empirical hormone assay panel. No brainer. Not terribly expensive, a little bit of effort required for logistics, but this would make the genetic data actually useful. In more ways than one.

Anyways, look do I think genes have a causal role in the probability of someone to be unfaithful? Fucking absolutely. I’d bet my life on it. It’s a no brainer. But did this study teach us literally anything useful? No. I don’t recognize any of their data points as being meaningful in any sort of interesting way. The whole thing is just underweight and full of questionable omissions (like my examples above) that I’m sure would have rendered p statistically insignificant.

Would these results replicate if the study was rerun? Probably. But we’d still not have learned anything at all.