In the 1830s, around 20,000 Cherokee Indians were uprooted from their traditional territories around the Smokey Mountains in Georgia, Alabama, and Tennessee and forced to begin a long march to a new home in Oklahoma. Infamously, many thousands would die on the trail. As the white settlers had expanded west in search of land and profits, the weaker natives were left with no choice but to take their chances and move, leaving rich and empty territory for the newcomers. This was the “Trail of Tears”, a brutal displacement of an entire people that has more or less been consigned to history.Yet competition, conflict, and war between peoples have not been consigned to history. While major wars between nation states have declined in recent decades, levels of inter-group violence within states in civil wars and between competing non-state actors, armed groups, and criminal organizations has remained at staggering levels.There is a new Trails of Tears, for example, taking place in Europe, as hundreds of thousands of Syrians flee the civil war there, hounded by multiple warring factions behind them and hindered by the increasingly parochial interests of the European states ahead of them. After last summer’s free-for-all migration across the EU’s open borders, one by one countries have erected razor-wire fences and locked down their borders. Thousands have died on this trail too, especially crossing the Mediterranean in flimsy and overloaded boats, in the outflow of territorial aggression that is hauntingly reminiscent of the ordeals of the Cherokee—and all too many other historical examples. Knoxville Workshop on Evolution and WarIn September 2015, a group of scholars gathered in Knoxville, Tennessee, close to the origins of the Trail of Tears, to consider the deep origins and persistence of war. Cognizant of our historical surroundings, we had come together to ask whether new light could be shed on the unending phenomenon of inter-group conflict and war from a different perspective: evolution. The workshop was hosted by University of Tennessee’s National Institute for Mathematical and Biological Synthesis (NIMBioS), whose mission is to bring together cross-disciplinary teams to develop mathematical and biological approaches to understanding a variety of complex systems—of which war is a good example. Our group included anthropologists, economists, historians, modelers, primatologists, psychologists, political scientists, and physicists, including many leaders in these fields such as Richard Wrangham, Kim Hill, and Polly Wiesner, as well as new blood in a competitively selected group of graduate students and post-docs.But what could an evolutionary perspective on war offer that other approaches could not? Two broad themes emerge. First, war may have been evolutionarily adaptive in our past, meaning that, although on the face of it war seems such a costly activity, fighting other groups brought net benefits to Darwinian fitness (reproductive success).[1] If so, then we would expect natural selection to have favored the evolution of adaptations that helped people to prepare, coordinate, and fight more effectively in inter-group conflicts (and this may have occurred via the processes of genetic selection among individuals, and/or as cultural evolution among groups). Hence, an evolutionary perspective may help us understand war as an adaptive strategy, just as it has helped us understand many other “nasty” traits such predation or fighting between individuals. It’s never good for the loser, but it can be a strategy that pays off on the average over the long term for the genes or groups that live on.Second, whether or not war was adaptive in our past, in today’s world it may incur net costs to all involved. Operating on such a large scale and with such lethal weapons, the marginal benefits may be outweighed by its enormous costs for winners and losers alike. But even or especially here, an evolutionary perspective can be helpful to understanding war, because it helps us to explain the conditions under which human beings become more or less motivated to fight. We can make predictions about how many of our evolved dispositions may cause or exacerbate conflict, ranging from well-known biases such as distrust of out-groups and overconfidence, to the desire for status and revenge). An evolutionary understanding of human nature helps us understand the contemporary conditions that encourage people to fight.But What’s New?While there has been a long history of applying biological and evolutionary ideas to warfare (Nazi sympathizers among them, but later on a much more serious group of sociobiology scholars), things are quite different today—and for the better. The gains have been threefold: concepts are better defined, theories are more nuanced, and the evidence is more abundant.First, and in many ways most importantly, “war” is recognized to be a broad term and numerous behaviors and dynamics play into it. Recent scholarship—as exemplified at the conference—has usefully broken down the phenomenon of war into a narrower and more explicit set of phenomena, which in turn makes operationalization possible and evolutionary hypotheses testable. For example, many presentations were actually about how humans manage to overcome the “collective action problem” facing war: although any given individual benefits from their group winning a war, why should that individual risk life and limb in participating? Without cooperation, there can be no war.[2]Second, clearer definitions have enabled greater nuance in theory building. We have a deeper understanding of the adaptive significance of war, and a better sense of why and when it may have been favored by selection. For example, among both chimpanzees and hunter-gatherers, lethal inter-group conflict tends to be restricted to situations in which the attacker has superior numbers and an element of surprise.[3] This is significant because, far from the chaos of modern battles with vast casualties on both sides, an “imbalance of power” makes attacking others both low-risk and effective—two vital criteria if natural selection is going to favor war. Research now draws on the insights of game theory, behavioral ecology, cross-cultural studies, and cultural evolution, rather than simplistic claims of innate aggression or the so-called “killer ape” hypothesis, which is both conceptually fuzzy and basically unfalsifiable—the cardinal sin of modern science.Third—and this is where the rubber meets the road—this scientific maturity has yielded a growing mountain of empirical evidence as to where, when, why, and how much war has been fought among pre-industrial societies around the world. These findings come not just from the accumulation of archeological and ethnographic data, but also from greater methodological rigour, new technologies, and more advanced methods of analysis. Although there are detractors,[4] a plethora of review volumes triangulating on the problem from a variety of disciplines and methods suggest that warfare is widespread among pre-industrial societies.[5] New findings include—importantly—the finding that warfare occurs among hunter-gatherer societies even when they are surrounded by other hunter-gatherer groups.[6] The old idea that inter-group conflict was imported by contact with outsiders has been resoundingly rejected for both chimpanzees and human warfare.[7] And in a stunning recent discovery, a massacre of 12 individuals at a site in Kenya 10,000 years ago has extended concrete evidence of inter-group conflict deep into our history.[8] Other work finds evidence that warfare has been instrumental in the evolution of human civilizations.[9]Although we peer humbly ahead into many remaining puzzles of conflict and violence, we do so on the shoulders of some remarkable giants, whose research now enables a sharper image of the problems of collective action, coalitional psychology, leadership and followership, strategy, social organization, patterns of conflict across human and non-human species, the role of weapons, the costs and benefits of individual participation in war, and cross-cultural variation in patterns of conflict. An added benefit of this approach is the opportunity to integrate these aspects to generate new ideas (for example, mathematical laws of combat developed in social science generate novel implications for the evolutionary advantages of coalitions).[10]These incremental advances do not translate into a simple consensus on why or how war evolved. However, the conference suggested at least a wide consensus that evolutionary theory offers a powerful lens for clarifying the ancient origins of war and provides a coherent deductive framework for explaining the proximate (mechanistic) and ultimate (functional) causes of war.The Varieties of War and the Commonalities of Human NatureOne intriguing aspect of evolutionary approaches to war is its focus on individual behavior. While war takes many forms—gang violence, terrorism, insurgency, rebellion, civil war, inter-state war—an important commonality is that they are fought, and led, by human beings. This makes evolutionary approaches relevant to them all (the cognitive adaptations we all share as human beings irrevocably set the tone and shape of coalitional aggression at all levels of analysis—even in modern international relations). It also suggests important variation in its manifestation that an evolutionary perspective may help to explain. For example, inter-group conflict in our evolutionary history involved small groups of more or less voluntary warriors, united in purpose, and fighting for home territory. Modern mass armies, directed from afar by politicians that are rarely at risk themselves, represent a significant “mismatch” of evolved traits and the costs and benefits that prevail for leaders and followers today. In short, we should expect that evolved traits might easily go awry in large-scale inter-state war, but that they may well remain highly adaptive among small-scale, kin-group conflicts that arise within, say, civil wars. While contemporary wars vary in many ways, there are fundamental evolutionary mechanisms and dynamics at play (such as in-group/out-group bias, collective action problems, coalitionary psychology, and so on) that make an evolutionary perspective relevant to war in all its forms. If we want to understand the beliefs and behavior of people locked in deadly conflict with each other, we first need to consider these traits in their natural context, and that means understanding war in human evolution.The Added Value of an Evolutionary PerspectiveWar is a complex process involving multiple interacting agents and institutions that defies simple explanation. However, the potentially powerful insights of evolutionary theory (the single best theory for understanding the behavior of any organism) is entirely omitted from the toolbox of most contemporary scholars and practitioners of war. This is not to exclude the all important political science, economics, and historical perspectives that have accumulated considerable data and theories on the causes of war already.[11] Nevertheless, evolution offers vital new perspectives and often counter-intuitive theories that add explanatory power over and above existing theories on why people are motivated to fight, and the conditions under which they are more likely to organize to do so.Given the unending list of conflicts around the globe, and the many failures of conflict resolution efforts, evolutionary approaches offer a range of novel predictions and empirical data that shed new light on the old problem of war. Steven Pinker is right that wars between nation states are in decline (at least for the moment), but conflict on the whole continues unabated, expanding in other forms as civil wars, non-state armed conflicts, and terrorism spread, and also finding new forms in cyber warfare and the geopolitics of outer space.[12] With conflicts raging in the Ukraine, Syria, Nigeria, Israel-Palestine, and future ones looming over Kashmir, the Arctic, and the South China Sea, social science theories are failing to fully succeed in explaining, predicting, or avoiding war.In what some hail as the century of biology, we and many leading experts gathered at the conference in Knoxville suggest that the simple step of recognizing humans as evolved organisms with a long history of war can only help, in some way big or small, to understand when and why people fight.References[1] Chagnon, N. A. (2014) Noble Savages: My Life Among Two Dangerous Tribes - The Yanomamo and the Anthropologists. New York: Simon & Schuster.[2] Tooby, J. & Cosmides, L. (1988) The evolution of war and its cognitive foundations. Institute for Evolutionary Studies Technical Report #88-1.[3] Wrangham, R. W. (1999) The Evolution of Coalitionary Killing, Yearbook of Physical Anthropology, 42: 1-30.[4] Fry, D. P. (Ed.). (2013) War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views. New York: Oxford University Press.[5] Allen, M. W. & Jones, T. L. (Eds.) (2014) Violence and Warfare among Hunter-Gatherers. Left Coast Press.[6] Wrangham, R. W. & Glowacki, L. (2012) Intergroup Aggression in Chimpanzees and War in Nomadic Hunter-Gatherers: Evaluating the Chimpanzee Model, Human Nature, 23: 5-29.[7] Wilson, M.L., et al. (2014) Lethal Aggression in Pan Is Better Explained by Adaptive Strategies Than Human Impacts, Nature, 513(7518): 414-417;[8] Mirazón Lahr, M., et al. (2016) Inter-group violence among early Holocene hunter-gatherers of West Turkana, Kenya, Nature 529: 394–398.[9] Turchin, P., et al. (2013) War, space, and the evolution of Old World complex societies. PNAS, 110, 16384–16389[10] Johnson, D.D.P. & MacKay, N.J. (2015) Fight the power: Lanchester's laws of combat in human evolution, Evolution and Human Behavior, 36 (2): 152-163.[11] Levy, J. S., & Thompson, W. R. (2010) Causes of War. Oxford: Wiley-Blackwell.[12] Pinker, S. (2011) The Better Angels of Our Nature: Why Violence Has Declined. New York: Viking.