Do you have the Ashley Madison gene?

| September 2, 2015
This article or excerpt is included in the GLP’s daily curated selection of ideologically diverse news, opinion and analysis of biotechnology innovation.

The Ashley Madison leak story has been dominating headlines, as men around the world find themselves squirming at the revelations. If you are unfamiliar with the scandal, here’s a primer: Ashley Madison is a dating website for people looking to have extramarital affairs. The Canadian based website boasts (or “boasted” might be the correct word) 37 million *profiles* created over the 14 year history of the site million from over 50 countries. Over the past month hackers released the names and credit card numbers of these users in a massive text file 35 gigabytes in size.

The shear size and difficulty of decoding the information means this story is here to stay but even in the five weeks since the initial release the story has provided some interesting and fun revelations. A lot of people are having affairs, or at least fantasizing about it. Many people at major corporations (like ESPN) have accounts through their work emails on the adultery website. Three zip codes in America do not have a single Ashley Madison user. In the coming weeks and month we will certainly see more interesting revelations from this leak.

Maybe the most scintillating stories emerging from the leak thus far have been how celebrities have dealt with the revelation that they had an account. Noted Christian Evangelist Josh Duggar and Vice President Joe Biden’s son Hunter have been on the hotseat and their responses could not have been any different. Duggar issued a publicly apology and more or less took the blame for his actions, calling himself a hypocrite and checking into rehab for sexual addiction. Hunter took the more nonsensical route of blaming “Russian agents” for creating a fake account to discredit him because of his Ukrainian business ties.

Evolving through trading

It may be little solace to the busted but science and evolution may provide a better excuse to use. Most mammals, or animals for that matter, don’t practice strict monogamy and human history is littered with infamous tales of adultery and polygamy. Yet, both practices are often seen as negative behaviors by society. This begs the question: are humans supposed to be monogamous and what do our genes and our evolution have to say about this quandary?

It may seem obvious that having more than one reproductive partner is evolutionarily advantageous. This is partly true as high reproduction rates benefits both the individual and the population by increasing genetic diversitywhich is important in a number of ways. For one it dilutes deleterious mutations in the overall gene pool — people with “bad: genes, such as those that cause diseases are less likely to pass them on. And, it creates novel gene combinations, which increase the chances that one or some of these combinations will be better suited to withstand a change in the environment. There is an overall loss of genetic diversity when a species moves from encouraging multiple partners to just one or a few exclusive partners.

But as all factors in natural selection/evolution there is a tradeoff. In giving up the ability to spread our seed more openly, we must have gained something. Trade offs are everywhere in evolution. One example is that compared to other mammals, we are slow, have duller senses and are comparatively weak. On the other hand our intelligence is unmatched in the Animal Kingdom, allowing us to compensate for our other flaws. Our ancestors probably had ape-like strength but at some point in our evolution we began committing more resources (i.e. energy) to developing stronger brains and less to developing stronger muscles. We selected for brains while trading away brute.

One theory suggests that monogamy evolved in our species because it reduced the chances of infanticide in early human communities. Males stuck to mating with one female and then stuck around to help rear these children because doing so increased the likelihood that those offspring would make it to reproductive age. This isn’t the only theory though. One competing idea is that females may have geographically spread out making it harder for males to find multiple reproductive partners. In this scenario males saved resources from not having to wander hostile tundra looking for mates. Proponents of both theories, although somewhat in conflict, agree that monogamy has been a part of human mating rituals for a long time.

Related article:  Prehistoric 'chewing gum' contains Neolithic girl's DNA, allowing scientists to reconstruct her face

Where we fit on the spectrum

So how did we get from guarding against infanticide to one in 4 married men in America having an Ashley Madison account? Some scientists speculate there may be a single gene that holds the answer to this question. Vasopressin is an important neurohormone that has been implicated in a variety of physiological processes but its primary role is in water retention and constricting blood vessels. Some evidence suggests the hormone is also involved in pair bonding and its receptor is highly expressed in reward circuits in the brain.

In the gene for one of the vasopressin receptors a short sequence can either be present, duplicated or absent. Men who have duplicates of the gene, are more likely to be single or in a marital crisis than those who had one copy or none. Men who have no copies of the sequence were significantly more likely to be in a stable marriage, while men who had one copy were somewhere in between.

When we also look to other primates for an answer we find an interesting dichotomy between primates that are mostly monogamous and those that are polygamous. In monogamous primates, like gibbons, we see a low degree of sexual dimorphism (males and females look very much the same) while in species that display polygamy, like chimps, we see a great deal of sexual dimorphism. In primates sexual dimorphism is generally expressed in size, males are bigger in height and weight. We also see males with larger genitals in those species that practice polygamy.

Where do humans fit on this spectrum? It’s tough to say. We are only slightly dimorphic in regards to size: more than in the monogamous primates but not to the drastic levels we see in polygamous primates. The same is true when comparing relative genital size to that of the two groups of primates. We do practice monogamy so on the behavioral spectrum we appear to be more like the monogamous primates. However, we are more genetically similar to the polygamous ones.

Getting back to Hunter Biden and Josh Duggar, maybe I was wrong. Evolution, genetics and science don’t really offer a definitive explanation for their behavior. Monogamy appears to be a part of our evolutionary story to some extent, and there is some data that monogamy in our ancestral line pre-dates the appearance of the Homo sapiens lineage.

On the other hand, plenty of evidence points to human mate choice as something that varies and is not definitively polygamous or monogamous. In reviewing the literature, the best description I found on the topic of characterizing human monogamy was from a 2011 paper published in Applied Evolutionary Psychology that described our behavior as “serial monogamy with clandestine adultery”–which when you think about it would be a perfect slogan for the next Ashley Madison.

Nicholas Staropoli is a research associate for the American Council on Science and Health. He has an M.A. in biology from DePaul University and a B.S. in biomedical sciences from Marist College. Follow him on twitter @NickfrmBoston

The GLP featured this article to reflect the diversity of news, opinion and analysis. The viewpoint is the author’s own. The GLP’s goal is to stimulate constructive discourse on challenging science issues.

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