The Evolutionary Arc of Human Warfare

As part of the Evolution of Human Wisdom Research Project, I’ve found myself reading scholarly works with a slightly different perspective than I used to. For example, a recent study confirming that Neanderthals made their own jewelry is both a significant methodological achievement but also an indicator that different human populations experimented with multiple ways to be human. I was thinking about how my perspectives have changed when I saw a new paper from Nature, suggesting that humans are inherently violent as they inherited this behavior from their mammalian ancestors. Can this project, which was designed in part to study how we became symbol users, help to shed light on this and other studies which seem to suggest humans are evolved to be violent?

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We often think of wisdom as a good thing, but is it also the basis for war? After all, however repugnant we find warfare, it is also at some level a type of cooperation. My colleague, Agustin Fuentes, has already blogged about it, and others have pointed out both pros and cons of the study. Scholars from anthropology to zoology have weighed in on the question, with two camps forming. One says that we inherited war from our ancestors, while the other argues that war is a recent human invention, only becoming common after the origins of cities. But what does the paleoanthropologist say?

When was the first murder? Of course, we have no archaeological evidence for the first time someone was intentionally killed, but we do have evidence from the Pleistocene of activities that may qualify as homicide, interpersonal violence, and even cannibalism. One of the earliest examples of what may be interpersonal aggression comes from Swartkrans in South Africa, where scientists reported cut marks on an australopithecine from over 2 million years ago. This fossil shows signs of being defleshed.[1] Was this an aggressive act? Perhaps. It could have also been part of a funerary practice. The latter may seem unlikely, as it perhaps makes these australopithecines seem “too human.” But, is that a good enough reason to suggest that there could not be a significant cultural practice? Most anthropologists would favor the aggressive act, and maybe even suggest it is an example of cannibalism, but without more contextual information, it is hard to say.

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There is, at some level, no shortage of early human fossils that show signs of violent deaths. One of the most interesting ones is a cranium from Sima de los Huesos, Spain, which has two fractures that are said to be due to blunt force trauma.[2] But, we need to be careful in how these fractures and other marks on the bone are interpreted. Taphomomy is the study of what happens to a bone from the time the animal dies till it is studied by a scientist. One difficult aspect of this is equifinality, which is when two different processes have the same outcome. Teasing apart what the actual cause of a broken bone was is quite difficult in the best of circumstances. For these reasons, it is often hard to know for certain what these surface modifications mean.

Sites such as Jebel Sahaba, Sudan (14,000 – 12,000 years ago) or Nataruk, Kenya (10,000 years ago) record multiple individuals, many of whom show signs of violent death. From a historical perspective they are indeed old. However, from a paleoanthropological perspective, these sites are actually fairly recent, occurring well after anatomically modern humans evolved in Africa 200,000 years ago. In some sense, perhaps the debate about if we are violent or not comes down to how we view the past. If we see humanity as something fairly recent, only taking hold once people settled down and built villages and cities, then it looks like the archaeological evidence shows violence is in our distant past. However, if you instead take the evolutionary arc approach, looking at how humans have changed over the deep time of human evolution, we can see that both violence and cooperation have evolved as different aspects of the human niche.

This fits with some of the work we’ve been doing here, trying to understand how and why humans began to use symbols. What is striking is that these early glimmerings of such artifacts are associated with non-anatomically modern humans. If these objects, such as the engraved clam shell from Trinil[3] or the eagle talon necklaces from Krapina[4], were found with classically defined Homo sapiens, then they would be seen as indictors of symbolic thought. But, they are often dismissed as ‘one-off’ examples of behaviors that did not take hold.

Yet, for some reason scholars have no problem pushing warfare and violence back into the Early Pleistocene. Human population densities were most likely fairly low throughout the Early and Middle Pleistocene. Much like the record for violence, the record of symbolic expression may be partially due to the fact that our ancestors were living in highly structured populations, with a low amount of gene flow between them. If there is limited gene flow, there would be limited movement of ideas, concepts, and artifacts. Similarly the need for warfare, as opposed to intragroup violence, would be less.

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Perhaps, the question—“if we are violent or not?”—is the wrong one to ask. As I’ve been telling colleagues all week, submitting an article titled “the phylogenetic roots of human cooperation” probably wouldn’t receive much attention. Yet, just as we are capable of awful things, so too are we able to help others in ways that are not connected to our fitness. Care of conspecifics is as human a trait as interpersonal violence, and has deep roots in the Pleistocene.[5] This project has taught me that theologians and anthropologists both have a lot to gain by taking a more nuanced perspective on our origins as a social species. What makes us humans is our shared evolutionary legacy, something which has both violent and peaceful aspects. If we emphasize one over the other, we will miss important behaviors that are at the root of our own wisdom.

[1] T.R. Pickering, TD White, N.Toth, “Brief Communication: cutmarks on a Plio-Pleistocene hominid from Sterkfontein, South Africa,” Am J Phys Anthropol 111 (2000): 579–584.

[2] N. Sala, J.L. Arsuaga, A. Pantoja-Pérez, A. Pablos, I. Martínez, R. M. Quam, et al., “Lethal Interpersonal Violence in the Middle Pleistocene,”  PLoS One 10 (2015): e0126589. doi:10.1371/journal.pone.0126589.

[3] J. Joordens et al., “Homo erectus at Trinil on Java used shells for tool production and engraving,” Nature 18 (2014): 228–231. doi:10.1038/nature13962.

[4] D. Radovčić et al, “Evidence for Neandertal Jewelry: Modified White-Tailed Eagle Claws at Krapina,” PLoS One 10 (2015): e0119802. doi:10.1371/journal.pone.0119802.

[5] P. Spikins, “How Compassion Made Us Human: The Evolutionary Origins of Tenderness, Trust and Morality,” (South Yorkshire: Pen & Sword Books Ltd; 2015).