Exploring The Genetic Basis of Enlistment

Maybe Uncle Sam wants you because you share genes …

The dividing line between nature and nurture has proved endlessly fascinating – and often contentious — both in and out of the academy. A new study appearing at SAGE Open puts a chit in the nature column as it suggests genes play a leading role in deciding on enlisting in the armed forces.

Based on an analysis of twins data found in the National Longitudinal Study of Adolescent to Adult Health, the authors examined the extent to which genetic, environmental or shared factors could explain whether or not an individual signs up for the U.S. military.

Genetic influences, they found, could account for 82 percent of the variance in lifetime military service, a finding that stood up in supplementary analyses controlling for age and gender. The remaining 18 percent was attributed to non-shared environmental influences.

“I think this paper illustrates one more time that there’s not much we can do to outrun the effects of our genes, in the same way that our environment plays an important role, too,” said Brian B. Boutwell, a criminologist at St Louis University and one of the paper’s four co-authors.

It’s familiar ground for them all. Boutwell, and two of his three military paper co-authors criminologists Kevin M Beaver of Florida State and J.C. Barnes of the University of Texas at Dallas, were co-authors of an edited volume that came out last year, The Nurture Versus Biosocial Debate in Criminology: On the Origins of Criminal Behavior and Criminality, which was structured as a debate and not a definitive answer. (The paper’s fourth co-author was Joseph Schwartz, a criminology and criminal justice professor at the University of Nebraska-Omaha.)

Boutwell, whose own research focuses in part of how genetic factors interact with environmental factors to predict crime, violence and other types of antisocial behavior, spoke with Social Science Space before the SAGE Open paper, “Enlisting in the Military: The Influential Role of Genetic Factors,” appeared online. (SAGE is the sponsor of Social Science Space.)

There is a fairly large literature on what leads someone to enlist, as well much research on improving recruitment, but their study, the authors believe, the first time someone has examined the genetic influence. Their findings in turn may change interpretations of that past research. “Prior research demonstrating family level influences on joining the armed forces, in actuality,” they wrote, “may be capturing a passive [gene-environment correlation]. If it were indeed the case that genetic factors influence selection into the military, then these same factors would inform propensities in the offspring of some parents towards military service.” (Their study, by the way, was not funded by the military or any outside agency.)

It’s not quite the same as saying there’s “combat in our genes,” however, and the authors are careful not to overstate what their data analysis suggests. “Although the results indicate that genetic factors account for more than three-quarters of the variance in military service, these findings should not be viewed as though genes determine who will and who will not service in the military,” they conclude, adding that other research shows how environmental influences can amplify or dampen genetic effects such as the one they show.

For their investigation, the authors drew from a commonly used subsample of 551 twin pairs drawn for National Longitudinal Study in the years between 1994 and 2008. Of the pairs, 217 were from the same zygote, i.e. they shared 100 percent of DNA. Similar methodology and sources, the authors note, have been used to estimate genetic and environmental influences “on virtually every human trait or behavior that can be studied,” and which consistently find genetic factors account for about 50 percent of the variance in the traits being examined.

Social Science Space: It’s obvious why someone would study this issue, but what lead you to study this issue?

Brian Boutwell: The biggest thing for us — and I believe I can speak a little bit for my co-authors on this as well — is that we have a broad interest in human nature and why people do the things that they do, why they make the choices that they make. This includes not just why the engage in illegal action versus why they would not, but also general life decisions: who might they choose for a mate, what might we select for a career.

How does joining the military fit into your previous work, and that of your co-authors, on more antisocial actions?

It certainly intersects in how people arrive at a certain choice in life, or how a set of tendencies or propensities of proclivities guide us and propel in certain directions. We do focus a lot on antisocial behavior, including things that are violent and illegal. In this case, with something like military involvement, the thought process is very similar in that whether we’re talking about an occupational status, or a particular set of behaviors, they aren’t randomly distributed throughout the population. There are certain personality traits that lend themselves to certain behavior.

Your 82 percent figure is pretty eye-opening in terms of genetic influence.

We weren’t necessarily shocked to see a figure that high. Currently, [the United States has] a standing military that is joined on a voluntary basis. So we would expect that individuals who are seeking out enlistment service in the military to some degree are doing so based on their personality traits, their temperament, their natural abilities, all of which through hundreds of twin studies to this point on various topics, all show these traits are influenced to some degree by genetic factors. Since we don’t have a draft or forced military conscription, we might expect that since the environment is held relatively constant that genetically influenced traits might explain more of the variance. And that’s exactly what we saw.

I notice you are being careful not to overclaim based on your findings.
To our knowledge this was one of the first studies that directly estimated the heritability coefficient of military involvement. And being first is something that warrants caution. Now, if the discussion had been about the heritability of behavior in general, there’s no reason, given the degree of evidence in that case, to be cautious.

To borrow a phrase from Stephen Pinker, military service offered us a window into the larger aspect of human nature. This is a very small part — we’re dealing with someone’s choice of occupation. On a larger plain, though, it illustrates that so many important aspects of human social life is influenced in meaningful ways by genetic factors. There’s still some fog over the genetic effects of daily human functioning — deciding what to do for a living, who to get married to. Genetic effects are intimately involved at all steps — as are things from the environment. I think this paper illustrates one more time that there’s not much we can do to outrun the effects of our genes, in the same way that our environment plays an important role, too. That’s not to say we’re ‘wired’ to do one thing or another; that’s not how genes work. But they do provide us a foundation for interfacing with the world.

It’s important to acknowledge that in the same way we acknowledge the importance of the environment. They are both involved in varying degrees to all the things we are interested in as social scientists, whether it’s why someone picks a particular career field or why someone attempts to violently brutalize another member of the population.

There have been peoples, whether they be Spartans or Prussians, who have had a strong martial tradition and ‘bred’ for a military life. Has that had any impact on your thinking?

It’s a reasonable question if we’re just talking about cultures that tend to be fairly militaristic. I don’t know that it informed our study a tremendous deal. But since we used a representative section of U.S. citizens, I don’t know what we’d find in a sample like you’re describing. It is an interesting question from an evolutionary standpoint: a trait that embodied proscribed aggression, acts of warfare, certainly has a long history in the evolution of our species.

There are other career choices that have similarities to the military, whether we’re talking about having a strict hierarchy or offering something for the adventurous. Do you think people can have a firefighting gene or a policing gene?

I think we can think about it more broadly, as temperaments well suited to a certain variety of fields versus temperaments well suited to a different variety of fields. For example, someone who is not averse to hyper-stimulating, hyper-arousing-type situations probably is not going to be put off by military service and the prospect of combat — or law enforcement — to some degree. That is not to say that there is a segment of DNA there to wire someone to be a police officer, but we can say there are personality styles that thrive in a situation like that.

There’s a lots of specialties in the military besides being an infantryman or being focused on combat. You could be a missileer, a pastry chef, an engineer, a bandsman …

That’s something that would be really nice to look at in future iterations. We were a little limited in sample size to be able to dive really deeply into which branch of the armed services someone selects, whether they served as an officer or an enlisted man, how fast they rose through the ranks. Interesting questions, but unfortunately not something we could address in this paper.

Your sample size was due in part to being stuck with twins?

It’s a wonderfully sized sample in terms of what samples are available. It’s certainly capable of doing a lot of meaningful things. We would have needed it bigger if, for example, we wanted to study enlistment in the Air Force versus in the Marines versus the Amy, Navy, Coast Guard.

There’s a large popular literature framed as either that the military is less and less representative of the U.S. population as a whole or that certain populations or regions are providing a disproportionate share of service members. This suggests some backing for your findings. Do you agree?

That might really be tapping into other issues that we weren’t able to get at with our studies. Some of that has to do with not being able to do the fine-grained analysis that you do if you had information about individuals who are enlisting versus individuals who are joining the military after completing an ROTC program in college versus individuals who go to a service academy. Could you see differences emerge across these categories? Possible. And some that might dovetail with what you’re alluding to in terms of a segment of the population being likely to join or be targeted for recruitment. It’s possible, but it would be premature for me to comment with any sort of certainty.

One would reasonably expect that area of the country — urban, rural, South, West — would inform the occupation that they select, the education that they obtain, where they can afford to live. There would still be selection forces at work, but not things we could access in a single twins study.

Could we see some sort of epigenetic effect that is handed down from the ‘Greatest Generation’ – the generation that volunteered in droves to fight in World War II — or some other period where patriotism created a larger-than-normal military?

That’s really a fascinating question. You’ve seen similar possibilities raised from generations that went through famine or severe deprivation and how that could play out two, three, four generations down the road in something like obesity. For military service? I hesitate to speculate too much. Epigenetics is a fascinating field, but how it relates to the intergenerational transmission of social behaviors as a result of altered gene expression is really still in its infancy. … If I were to hazard a bit of a very cautious, informal guess, I wouldn’t expect to see it play out with an increased likelihood of joining the military for generations that have come after the ‘Greatest Generation’.

You and your co-authors suggested there might be recruiting strategies that could wheel off your findings?

One of the broad things that could be extracted from our analysis is that in order to genuinely know if a particular recruiting strategy is effective, you would need to parse out the effects of genes that we’ve observed. Simply because two variables correlate with each other doesn’t imply with any degree of certainty that one is causing the other. So if you have a recruiting strategy that even if it’s increasing the number of individuals seeking out military service, knowing what we know from our study (and hopefully more to come), it should cause at least some pause as to whether these recruiting strategies are having a causal impact.

Is there any reason to think there is something unique to the U.S. military in this regard?
It would depend on many other factors. Is military service conscripted in any way – are you dealing with a culture where everyone has to serve in some way? That will alter your findings. Heritability estimates are subject to change. In our sample, it necessitated that we have a voluntary military service – otherwise you have less variation to deal with. It wouldn’t shock me if the results came out the same way, maybe not a heritability estimate as high as what we found, but something certainly above zero, in other nations.

What’s next?

The next interesting step is we really want to dive more into what these findings represent. For example, are there differences in the heritability estimates for different branches of the armed services? I can’t think of a reason there would be off the top of my head, but really don’t know until these studies are done. I think a fascinating question to ask is if there was a way to dive into occupations within the military that people seek out because they have a higher probability of combat or risk. Or what predicts success for people who rise very quickly?