Some years ago, I was in a conversation with my wife reminiscing on my younger years when I was in the Marine Corps. At times, she could be quite taken aback at stories of the various antics Marines got into, particularly with how we treated one another. Casual interaction often involved talking with each other in ways that most people would consider vicious insults, or horseplay that would in most contexts probably be referred to as assault. On one occasion she asked me, “Why were you guys always so awful to each other?” And my immediate response was “For the same reason monkeys poke each other in the eyes.”

On the off-chance that this doesn’t clear things up for you, let me elaborate. 

I had recently read a book called Games Primates Play: An Undercover Investigation of the Evolution and Economics of Human Relationships. The book looks at social behavior among various primates and illustrates how that behavior is also reflected within human institutions and norms. One form of behavior common among primates is loyalty signaling, and alliance building, by means of the infliction of minor harms. 

For example, some monkeys take it in turn to deliberately expose vulnerable parts of themselves to another, and allow that other monkey to prod, poke, or grip these areas. Afterwards, the routine is repeated in the other direction. The effective signal here is, “If I had wanted to, I could have just inflicted a devastating injury on you, but I did not. And I allowed you to be able to inflict a devastating injury on me, but you did not either. Now we know that we can trust each other, because we both just had a perfect chance to cause serious harm but didn’t do so.” The book included, among other illustrations, pictures of monkeys taking it in turn to poke each other in the eyes as part of this routine. 

A similar cultural norm was always in effect in the Marines. The unspoken understanding was “You can insult me in the most over-the-top ways imaginable and I will not be upset – indeed, I will laugh along with you. And I can do the same to you, and you’ll laugh along with me too.” In the same way, the norm regarding the rough-and-tumble aspect of Marine culture showed the same signal. As was once put by Max Uriarte, the Terminal Lance himself:

The phenomena associated with birthdays in the Marine Corps is second to none. Mention it’s your birthday, someone else’s birthday–even your mother’s birthday–and you will be literally physically assaulted. The birthday in the Marine Corps is a dangerous time, lay low for the day and hope no one remembers tomorrow; lest ye find themselves in a world of angry, blind rage. In a way, this angry hurricane of fist and contusion is the Marines’ way of showing their affection for their fellow companion.

I recall my 21st birthday. October 11th, 2007–Iraq. While I assure you my beating was substantial, I remain confident that it was ultimately out of affection.

While these antics are taken to further extremes in the Marine Corps than it is among normal (civilized?) people, the same ideas apply. When you get to know someone and they fall into the realm of “casual acquaintance,” the social norm is to be polite, overlook flaws, pretend not to notice potentially embarrassing gaffes, and so forth. But when you move into friendship, things change. Friends tease each other, they make fun of each other, they jokingly highlight embarrassing gaffes rather than pretend not to notice, they play practical jokes, and so on. And often, making a move like this is how one signals to another that the relationship has moved from casual acquaintance into real friendship.

I’m sure I’m not the only one who has, at times, felt like such a transition had occurred, and made the first move into “poking friendly fun” at the other person, only to have that person become genuinely upset, making me realize that perhaps they and I hadn’t grown as close as I had thought. (It can’t be just me, right?) And this is also why such behavior is taken to relative extremes in the military. In the Marine Corps, people needed to be able to stick together in extreme, high pressure environments with life-and-death stakes. That kind of cohesion requires that people can’t have walls up against each other – so day to day life greatly depended on regularly demonstrating that all walls were down. So no matter how viciously you insulted me or I insulted you, we would both be laughing about it together over beers at the barracks later that night. 

And therein lies the other side of the coin – signaling of this sort doesn’t really send much of a signal if it doesn’t have at least the potential to cost something. Attempting to signal friendship by engaging in behavior that’s indistinguishable from the polite, anodyne behavior among acquaintances sends an invisible signal. Sometimes, signals are misread, and jokes or actions are taken that cause people to become genuinely upset. But if that risk wasn’t there, there would be no signal. 

Over the course of my life, I’ve witnessed a number of top-down pushes, both formal and informal, to try to replace these mildly antagonistic forms of friendship signaling in favor of a kinder, gentler society. But if the thesis of Games Primates Play is right, it may not be the case that the kinder, gentler social interaction serves as a real substitute for building social cohesion, because these ideas are deeply embedded in our evolved psychology.

If a monkey committee decided that eye-poking was needlessly antagonistic behavior and prevented monkeys from engaging in these behaviors, the end result would not be a greater level of social cohesion among that troop. It would lead to a breakdown of the social order on which the troop relies. And there’s a real possibility that the modern push to move social environments into “kinder, gentler” places where mildly antagonistic behavior is forbidden may backfire. Rather than strengthening social bonds, it may only serve to weaken the fabric that keeps social bonds strong.