The War Instinct

In late February of 1991, as I straddled the border between Saudi Arabia and Iraq in my fatigues, I asked myself a question I’ve recently heard from my students: “Will we always have war?” To answer it, I have concluded, we must first decide what we mean by “war.”

Until recently, the term had a deceptively simple definition: war was a period of open and declared armed hostile conflict between two states or nations. But the Sept. 11 attacks and our resulting “War on Terror” show the limits of the traditional concept. War doesn’t require nations at all. In fact, from my standpoint as a biologist, war doesn’t even require humans.

In my view, war is coordinated aggression between two or more groups within a species—any species. The most common triggers are the desires or needs for territory, resources or mates. Ants are a well-known example. Ant wars are most likely to happen after periods of rapid colony growth, when the need for territorial expansion becomes dire. War may thus be an unfortunate, but natural, outcome of overcrowding driven by population growth or territory reductions.

And we don’t need to look far down our evolutionary tree to see the outcome of territorial disputes. Chimpanzees have been known to brutally kill neighbors over resources. The methods employed by our relatives are less like the large-scale combat of ants and more like special ops. Moving with stealth, troops of males penetrate the borders of a neighboring clan and start killing. If war includes killing that goes on sequentially instead of simultaneously, then chimps wage war.

Knowing that ants, chimps and others engage in wars over territory may not add much to our understanding of the basic nature and triggers of war. Indeed, I stood on the Iraqi border in 1991 precisely because Kuwait had oil that Iraq coveted. But knowing that war is not unique to humans, that we didn’t invent it, is darkly informative. It suggests that war stems from a biological trait—and biological traits, as we know, can be overcome. If war were a quirk of evolution and nothing more, we might manage to deposit it on the scrapheap of history.

But with human warfare, both evolution and culture play a role. Our evolved tendencies relate to survival and reproduction, and these things are at least tangible, measurable. Historically, acquiring resources to support these tendencies would have involved personal risk, and thus would have lent itself to some rational cost-benefit analysis. Where we differ from other warring species is in the cultural reasons we slaughter each other: for religion, for honor, for “our way of life.”

Not only do we invent intangible excuses for war, we do something that no other animals do: we have individuals declaring war while leaving the fighting to others. A rational cost-benefit analysis is impossible when what you fight for is immeasurable, and when those who declare war do not incur the risks of those who prosecute it. For humans today, in large part, war is a cultural trait with evolutionary roots. In a world where resources are being depleted, populations are growing and philosophical divides are expanding, we will have to battle both nature and culture if we want to see the end of war.

On an individual level, that battle can be won. After returning from the front lines of the Persian Gulf War, I received my third and final honorable discharge from the U.S. Army—this last one as a conscientious objector. It remains unclear to me, however, if that battle can be won at the collective level.

Moving beyond war depends on our ability to resist evolved tendencies and to reject cultural ones. Resisting evolved tendencies is easier than you might think. Selection maximizes fitness, not happiness, and once you recognize that some biological urges—such as cheating on your partner—are likely to decrease your long-term happiness, you can use your cultural knowledge to make better decisions.

Cultural tendencies are more insidious. We are social animals who form, and defend, groups. When groups collide, group identity often trumps individual identity. And when you believe that what you are fighting for—religion or honor, for example—will ultimately bring you or your family happiness, then fighting may feel worth the sacrifice. As such, my answer to the question “Will we always have war?” is ever the same: “I hope not, but I fear so.”

This article first appeared in the Winter 2014 issue of Tufts Magazine.

Philip Starks, an associate professor of biology at Tufts, studies the social behavior of animals.