If you're someone who likes casual sex with multiple partners (and since you reading this blog, chances are you are one of us), you've probably wondered why you like it. And you've probably heard all sorts of possible answers for this why - liberal sexual values, early sexual experience, porn, daddy issues, sexual trauma, low self-esteem... you name it.
While these environmental factors can contribute to some people's sluttiness (a topic for another time), there is one factor that leads to greater interest in hookups and multiple partners that often gets neglected: genetics. Yup, pure old genetics.
We've known for a while that our sexual life history (things like age at first intercourse, age at first pregnancy, age at puberty etc) are partially genetically determined. Now a new genome-wide association study (GWAS) of over 1 million people (the largest genetic study of this kind ever!) identifies no fewer than 117 different genetic variants (SNPs or single nucleotide polymorphisms) that are involved in determining people's lifetime number of sexual partners.
Much of this boils down to our comfort with sexual risk taking.
Hookups with people you don't know well are undoubtedly riskier--emotionally, physically, socially, health-wise--than sex with one long-term partner. But some of us find this kind of sexual risk taking incredibly exciting and rewarding; others find it incredibly aversive and anxiety-producing. This tolerance or aversion to sexual risk is what's (partly) determined by these genes.
General vs domain-specific risk tolerance
Sexual risk taking is not an isolated trait. Our propensity for risk taking in one domain (say, skydiving) is to some extent correlated with our propensity for risk taking in another domain (say, financial investments). If you like to jump out of airplanes, you're also somewhat more likely to make riskier financial investments. In other words, each of us has a general level of risk-taking we are comfortable with, even if it manifests differently in different people.
This has been long established by social science research that simply asks people about their risk tolerance across various life domains. But this new study further confirmed this link on a genetic level. The 80-200 genetic variants involved in the four specific types of risk taking the researchers asked about - drinking, smoking, fast driving, and number of sex partners--overlapped greatly with the 100+ genetic variants involved in people's general propensity for risk taking and sense of adventurousness.
In fact, the genetic overlap between these various risk-taking domains was much larger than the phenotypic (ie. behaviorally expressed) overlap found in surveys. In other words, there is only a weak correlation between people's reported tendency for skydiving versus starting their own business versus doing cocaine, but the genes coding for these different types of risk-taking activities overlap quite a bit.
The study authors interpret this finding to mean that our genes are more responsible for our general level of risk-taking propensity, but our environments are more responsible for the exact ways that this propensity will manifest itself. For example, you and I may have been born with the same general propensity for risk tolerance due to the same risk-taking genes (more or less), but your upbringing and personal experiences may have pushed you more toward risky financial investments while mine may have pushed me more toward sexual adventures.
Using several other genome-wide association samples, this study even found that the genes for risk-taking (general and domain-specific) greatly overlapped with the genes for some basic personality traits: extraversion and openness to experience, and lower neuroticism. And, the risk-taking genes also overlapped with the genes for some psychiatric disorders: attention deficit and hyperactivity disorder (ADHD), schizophrenia, and bipolar disorder. All this all suggests that there is a genetic commonality to all of these psychological characteristics.
How "guilty" are genes, exactly?
Before you conclude that your (or anyone else's) slutiness is fully to blame (or thank?) on your genes, read this: Taken together, the 100+ genetic variants identified as involved in sexual risk-taking accounted for only about 1% of the variation in the number of sexual partners across individuals. In other words, plenty of room for other environmental factors to influence your love of hookups.
[Although, this brings up an old population genetic conundrum: The missing heritability problem. Many twin studies have suggested that the overall heritability of risk-taking (and lots of other psychological characteristics) in the population is about 30-40% (with the rest due to environmental influences). At the same time, studies looking directly at genes (whether individual gene candidates or these genome-wide association studies) have never been able to find evidence of that much genetic influence. If you want to read more about this issue, Wikipedia has a pretty intelligible post about it.]
Wait, but it's not dopamine??
Perhaps the most surprising aspect of this study is that the 100+ risk-taking genetic variants identified in the study were NOT associated with the usual genetic suspects when it comes to risk-taking: dopamine & serotonin (the reward chemicals), testosterone & estrogen (the sex hormones), and cortisol (the stress hormone).
(Although they did find that some of brain regions where the risk-taking genetic variants were most expressed--the reward system--are areas where dopamine and serotonin play important roles.)
Instead, the risk-taking genetic variants the study identified seemed to congregate in parts of the genome responsible for two chemicals: glutamate (the main excitatory neurotransmitter in the brain) and GABA (the main inhibitory neurotransmitter in the brain). These results suggest that the balance between excitatory and inhibitory neurotransmission in the brain may contribute to variation in general risk tolerance across individuals.
There you go. You can partially blame (ie., thank) your genes for your love of hookups.
Take good care, everybody. Remember to love yourselves and find ways in which to support others in our LGBTQ community.