09/12/2009 05:12 am ET Updated May 25, 2011

Evolution and War: Back to Basics

War has been part of the human condition throughout recorded and archeological history. Violent between-group conflict is also part of nature, from epic battles between ant colonies, to the territorial conflicts of lion prides, to the raiding parties of chimps.

Is war part of our nature? That question has been debated throughout intellectual history. Since Darwin, it has been framed in terms of evolutionary theory, since the "nature" of anything requires a consideration of evolution.

Now that evolution has grown into a sophisticated science, it would be nice to think that discussions of war from an evolutionary perspective have kept pace. Alas, a recent article titled "Winning the Ultimate Battle: How Humans Could End War" indicates otherwise. The article is by John Horgan, a respected science writer, cites respected sources, and is published in the respected journal New Scientist. Yet, it fails Evolution 101. I wish that a basic tutorial wasn't necessary, but here goes.

Evolution 101. No organism, not even a virus, is so simple that it behaves the same way under all circumstances. Most behaviors that evolve by natural selection take the form of "do X in this situation and do Y in that situation", rather than "always do X". An obvious example is human skin color. Populations that lived in permanently sunny locations evolved skin that is permanently dark. Populations that lived in locations where sun exposure varies evolved the ability to alter their skin color accordingly -- tanning. Both count as biological adaptations that evolved by genetic evolution.

The fact that tanning is a physiological process rather than a behavior illustrates an important insight that emerged over the last half century of evolutionary research. Behaviors are sensitive to context almost by definition. Even breathing, which we do all the time, is sensitive to the level of C02 in our blood. Part of the accomplishment of early ethologists such as Konrad Lorenz, Niko Tinbergen, and Karl Von Frisch was to show that behaviors evolve by natural selection, just like morphological, physiological, and life history traits. It wasn't until later, however, that evolutionists began to realize that these non-behavioral traits are often like behaviors in their sensitivity to context.

For example, many aquatic organisms have evolved to develop into very different morphological forms, depending upon the presence of chemicals in minute quantities that indicate the presence of their predators. This is called adaptive phenotypic plasticity. It is a biological adaptation that evolves by genetic evolution when species encounter a range of environments requiring different phenotypes during their evolutionary history. All the traits that are traditionally considered "nonbehavioral" (morphology, physiology, life history) can evolve to be phenotypically plastic, in addition to behaviors that have always been known to be sensitive to context.

Adaptive phenotypic plasticity is like a computer program with "if" statements, which branches in different directions depending upon information entered into the program. No evolutionist in her right mind would say that adaptive phenotypic plasticity fails to qualify as a biological adaptation because it is sensitive to environmental context.

Failing the test. Against this background, let's follow Horgan's argument against the innateness of war. He begins with the observation that most people regard war as inevitable, frequently adding that it is "part of human nature" and "in our genes". He then challenges this conclusion by providing evidence that war is not everywhere all the time. I think you can see how he is on his way to flunking Evolution 101. Here is how he supports his argument:

• The work of anthropologist Robert Sussman is used to claim that people are cooperative more often than aggressive. For Horgan, this means that "the urge to wage war is not innate".

• The extensive cross-cultural research of anthropologists Carolyn and Melvin Ember is used to show that the vast majority of human cultures do experience war, but at different frequencies. For Horgan, this provides evidence to support the assertion that "biology alone cannot explain documented patterns of warfare".

• The work of anthropologists Douglas Fry and Brian Ferguson is used to claim the existence of 74 "non-warring cultures" during the recent past and the lack of clear-cut evidence for war prior to 14,000 years ago. For Horgan, this information contradicts "the idea that war is universal".

Here is the bottom line according to Horgan:

"So, rather than being a product of our genes, it looks as if warfare emerged in response to a changing life style. Even then it was far from inevitable, as the variability of warmongering between cultures and across time attests."

I hope it is obvious that Horgan has merely demonstrated that war is sensitive to context, just like any other phenotypically plastic trait. Suppose that the human propensity to wage war evolved by genetic evolution as a hard-wired if-then rule: "Wage war in situation X, otherwise wage peace." Now suppose that a) situation X occurs at a low frequency in hunter-gatherer environments; b) situation X began to occur at a higher frequency with the advent of agriculture; and c) situation X became highly variable across cultures with the advent of agriculture. According to this scenario, warfare is just as innate as our ability to suntan and accounts for all the evidence that Horgan assembles against the innateness of war. Horgan's argument is so lame that if he was a student in my 100-level evolution course for non-majors, I would flunk him.

What's culture got to do with it? Even more lamentable is the way that Horgan creates a dichotomy between "genes", "biology", "innate" and "evolution" on one hand, and "culture" on the other hand, as if human culture lies completely outside the orbit of evolutionary theory. This view is common among postmodernists but is an embarrassment coming from a science writer such as Horgan and the scientists that he cites, to the extent that Horgan properly represents their views.

One of the most exciting growth areas of evolutionary theory is the study of culture as a genetically evolved capacity for open-ended change, as described by books such as Not By Genes Alone: How Culture Transformed Human Evolution by Peter Richerson and Robert Boyd, and my own Evolution for Everyone. To see how modern theories of cultural evolution bear upon the subject of war, let's return to the comparison of some human populations that have dark skin all the time while others have the ability to tan. The reason is because some populations experienced a constant environment while others experienced a variable environment during their evolutionary pasts, with respect to exposure to the sun. Now imagine that humans are not hard-wired to wage war in situation X, in contrast to the scenario that I outlined above. Instead, humans have a more open-ended capacity for acquiring and transmitting behaviors based on their experience, which enables them to adapt to their environments faster than the slow process of genetic evolution.

Continuing the new scenario, imagine that some human populations never experience the environmental conditions that would favor war. War would not evolve by genetic evolution, and it doesn't evolve by cultural evolution either. Other human populations experience the conditions that favor war some of the time. We expect a context-sensitive ability to wage war to evolve by cultural evolution, just as it would evolve by genetic evolution. Finally, if some human populations experience war all the time, we expect them to lose the capacity to wage peace, even if the opportunity arises in the future. That ability would need to evolve by an ongoing process of cultural evolution.

I hope it is obvious that this cultural evolutionary story about war is exactly parallel to the genetic evolutionary story about sun tanning. The capacity of a given culture to "do X" in a given situation depends upon whether that situation has existed during its evolutionary past -- in this case its cultural rather than its genetic evolutionary past. A genetic evolutionary story is still needed, however, to explain our capacity for open-ended cultural change.

If cultures exist that are truly "non-warring", in the sense that they have no capacity to wage war under any circumstance, that would count as evidence against my first scenario but would still exist firmly within the orbit of evolutionary theory according to my second scenario. More generally, those who emphasize the human capacity for open-ended change can pursue their vision better by becoming knowledgeable about evolutionary theory, rather than imagining that they are opposed to it.

Increasing the quality of discourse. It is discouraging that the quality of discourse about the human propensity to wage war is still so low that it flunks Evolution 101. Even worse, the same illiteracy exists for innumerable other subjects just as important for human welfare. In an effort to solve this problem, I have become involved in the creation of a new think tank called the Evolution Institute, which will provide a conduit from the world of contemporary evolutionary theory to the world of public policy formulation. Visit our website to learn about and join our enterprise. Judging from the example that I have recounted here, we have a lot of work to do.