Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

  By the time of Pinker’s synthesis, HG violence was established, and the percentage of their deaths attributed to warfare averaged around 15 percent, way more than in modern Western societies. Contemporary HG violence constitutes a big vote for the Hobbesian view of warfare and violence permeating all of human history.

  Kalahari !Kung hunter-gatherers

  Time for the criticisms:73

  Mislabeling—some HGs cited by Pinker, Keeley, and Bowles are, in fact, hunter-horticulturalists.

  Many instances of supposed HG warfare, on closer inspection, were actually singular homicides.

  Some violent Great Plains HG cultures were untraditional in the sense of using something crucial that didn’t exist in the Pleistocene—domesticated horses ridden into battle.

  Like non-Western agriculturalists or pastoralists, contemporary HG are not equivalent to our ancestors. Weapons invented in the last ten thousand years have been introduced through trade; most HG cultures have spent millennia being displaced by agriculturalists and pastoralists, pushed into ever tougher, resource-sparse ecosystems.

  Once again, the cherry-picking issue, i.e., failure to cite cases of peaceful HGs.

  Most crucially, there’s more than one type of HG. Nomadic HGs are the original brand, stretching back hundreds of thousands of years.74 But in addition to HG 2.0 equestrians, there are “complex HGs,” who are different—violent, not particularly egalitarian, and sedentary, typically because they’re sitting on a rich food source that they defend from outsiders. In other words, a transitional form from pure HGs. And many of the cultures cited by Ember, Keeley, and Pinker are complex HGs. This difference is relevant to Nataruk, that northern Kenyan site of a ten-thousand-year-old massacre—skeletons of twenty-seven unburied people, killed by clubbing, stabbing, or stone projectiles. The victims were sedentary HGs, living alongside a shallow bay on Lake Turkana, prime beachfront property with easy fishing and plentiful game animals coming to the water to drink. Just the sort of real estate that someone else would try to muscle in on.

  The most thoughtful and insightful analyses of HG violence come from Fry and from Christopher Boehm of the University of Southern California. They paint a complex picture.

  D. P. Fry and P. Söderberg, “Lethal Aggression in Mobile Forager Bands and Implications for the Origins of War,” Sci 341 (2013): 270.

  Visit bit.ly/2oeg96t for a larger version of this graph.

  Fry has provided what I consider the cleanest assessment of warfare in such cultures. In a notable 2013 Science paper, he and Finnish anthropologist Patrik Söderberg reviewed all cases of lethal violence in the ethnographic literature in “pure” nomadic HGs (i.e., well studied before extensive contact with outsiders and living in a stable ecosystem). The sample consisted of twenty-one such groups from around the world. Fry and Söderberg observed what might be called warfare (defined by the fairly unstringent criterion of conflict producing multiple casualties) in only a minority of the cultures. Not exactly widespread. This is probably the best approximation we’ll ever get about warfare in our HG ancestors. Nonetheless, these pure HGs are no tie-dyed pacifists; 86 percent of the cultures experienced lethal violence. What are their causes?

  In his 2012 book Moral Origins: The Evolution of Virtue, Altruism, and Shame, Boehm also surveys the literature, using slightly less stringent criteria than Fry uses, producing a list of about fifty relatively “pure” nomadic HG cultures (heavily skewed toward Inuit groups from the Arctic).75 As expected, violence is mostly committed by men. Most common is killing related to women—two men fighting over a particular woman, or attempts to kidnap a woman from a neighboring group. Naturally, there are men killing their wives, usually over accusations of adultery. There’s female infanticide and killing arising from accusations of witchcraft. There are occasional killings over garden-variety stealing of food or refusals to share food. And lots of revenge killings by relatives of someone killed.

  Both Fry and Boehm report killings akin to capital punishment for severe norm violations. What norms do nomadic HGs value most? Fairness, indirect reciprocity, and avoidance of despotism.

  Fairness. As noted, HGs pioneered human cooperative hunting and sharing among nonrelatives.76 This is most striking with meat. It’s typically shared by successful hunters with unsuccessful ones (and their families); individuals playing dominant roles in hunts don’t necessarily get much more meat than everyone else; crucially, the most successful hunter rarely decides how the meat is divided—instead this is typically done by a third party. There are fascinating hints about the antiquity of this. Big-game hunting by hominins 400,000 years ago has been documented; bones from animals butchered then show cut marks that are chaotic, overlapping at different angles, suggesting a free-for-all. But by 200,000 years ago the contemporary HG pattern is there—cut marks are evenly spaced and parallel, suggesting that single individuals butchered and dispensed the meat.

  This does not mean, though, that sharing is effortless for pure HGs. Boehm notes how, for example, the !Kung perpetually kvetch about being shortchanged on meat. It’s the background hum of social regulation.

  Indirect reciprocity. The next chapter discusses reciprocal altruism between pairs of individuals. Boehm emphasizes how nomadic HGs specialize, instead, in indirect reciprocity. Person A is altruistic to B; B’s social obligation now isn’t necessarily as much being altruistic to A as paying the altruism forward to C. C pays it forward to D, etc. . . . This stabilizing cooperation is ideal for big-game hunters, where two rules hold: (a) your hunts are usually unsuccessful; and (b) when they are successful, you typically have more meat than your family can consume, so you might as well share it around. As has been said, an HG’s best investment against future hunger is to put meat in other people’s stomachs now.

  Avoidance of despotism. As also covered in the next chapter, there’s considerable evolutionary pressure for detecting cheating (when someone reneges on their half of a reciprocal relationship). For nomadic HGs, policing covert cheating is less of a concern than overt evidence of intimidation and powermongering. HGs are constantly on guard against bullies throwing their weight around.

  HG societies expend lots of collective effort on enforcing fairness, indirect reciprocity, and avoidance of despotism. This is accomplished with that terrific norm-enforcement mechanism, gossip. HGs gossip endlessly, and as studied by Polly Wiessner of the University of Utah, it’s mostly about the usual: norm violation by high-status individuals.77 People magazine around the campfire.* Gossiping serves numerous purposes. It helps for reality testing (“Is it just me, or was he being a total jerk?”), passing news (“Two guesses who just happened to get a foot cramp during the hairiest part of the hunt today”), and building consensus (“Something needs to be done about this guy”). Gossip is the weapon of norm enforcement.

  HG cultures take similar actions—collectively subjecting miscreants to criticism, shaming and mockery, ostracizing and shunning, refusing to share meat, nonlethal physical punishment, expulsion from the group, or, as a last resort, killing the person (done either by the whole group or by a designated executioner).

  Boehm documents such judicial killings in nearly half the pure HG cultures. What transgressions merit them? Murder, attempts at grabbing power, use of malicious sorcery, stealing, refusal to share, betrayal of the group to outsiders, and of course breaking of sexual taboos. All typically punished this way after other interventions have failed repeatedly.

  —

  So, Hobbes or Rousseau? Well, a mixture of the two, I say unhelpfully. This lengthy section makes clear that you have to make some careful distinctions: (a) HGs versus other traditional ways of making a living; (b) nomadic HGs versus sedentary ones; (c) data sets that canvass an entire literature versus those that concentrate on extreme examples; (d) members of traditional societies killing one another versus members being killed by gun-toting, land-grabbing outsiders; (e) chimps as our cousin
s versus chimps erroneously viewed as our ancestors; (f) chimps as our closest ancestors versus chimps and bonobos as our closest ancestors; (g) warfare versus homicide, where lots of the former can decrease the latter in the name of in-group cooperation; (h) contemporary HGs living in stable, resource-filled habitats with minimal interactions with the outside world versus contemporary HGs pushed into marginal habitats and interacting with non-HGs. Once you’ve done that, I think a pretty clear answer emerges. The HGs who peopled earth for hundreds of thousands of years were probably no angels, being perfectly capable of murder. However, “war”—both in the sense that haunts our modern world and in the stripped-down sense that haunted our ancestors—seems to have been rare until most humans abandoned the nomadic HG lifestyle. Our history as a species has not been soaked in escalated conflict. And ironically Keeley tacitly concludes the same—he estimates that 90 to 95 percent of societies engage in war. And whom does he note as the exceptions? Nomadic HGs.

  Which brings us to agriculture. I won’t pull any punches—I think that its invention was one of the all-time human blunders, up there with, say, the New Coke debacle and the Edsel. Agriculture makes people dependent on a few domesticated crops and animals instead of hundreds of wild food sources, creating vulnerability to droughts and blights and zoonotic diseases. Agriculture makes for sedentary living, leading humans to do something that no primate with a concern for hygiene and public health would ever do, namely living in close proximity to their feces. Agriculture makes for surplus and thus almost inevitably the unequal distribution of surplus, generating socioeconomic status differences that dwarf anything that other primates cook up with their hierarchies. And from there it’s just a hop, skip, and a jump until we’ve got Mr. McGregor persecuting Peter Rabbit and people incessantly singing “Oklahoma.”

  Maybe this is a bit over the top. Nonetheless, I do think it is reasonably clear that it wasn’t until humans began the massive transformation of life that came from domesticating teosinte and wild tubers, aurochs and einkorn, and of course wolves, that it became possible to let loose the dogs of war.

  SOME CONCLUSIONS

  The first half of the chapter explored where we are; the second, how we most likely got here.

  “Where we are” is awash in cultural variation. From our biological perspective, the most fascinating point is how brains shape cultures, which shape brains, which shape . . . That’s why it’s called coevolution. We’ve seen some evidence of coevolution in the technical sense—where there are significant differences between different cultures in the distribution of gene variants pertinent to behavior. But those influences are pretty small. Instead what is most consequential is childhood, the time when cultures inculcate individuals into further propagating their culture. In that regard, probably the most important fact about genetics and culture is the delayed maturation of the frontal cortex—the genetic programming for the young frontal cortex to be freer from genes than other brain regions, to be sculpted instead by environment, to sop up cultural norms. To hark back to a theme from the first pages of this book, it doesn’t take a particularly fancy brain to learn how to motorically, say, throw a punch. But it takes a fancy, environmentally malleable frontal cortex to learn culture-specific rules about when it’s okay to throw punches.

  In another theme from the first half, cultural differences manifest themselves in monumentally important, expected ways—say, whom it is okay to kill (an enemy soldier, a cheating spouse, a newborn of the “wrong” sex, an elderly parent too old to hunt, a teenage daughter who is absorbing the culture around her rather than the culture her parents departed). But the manifestations can occur in unlikely places—e.g., where your eyes look within milliseconds of seeing a picture, or whether thinking of a rabbit prompts you to think of other animals or of what rabbits eat.

  Another key theme is the paradoxical influence of ecology. Ecosystems majorly shape culture—but then that culture can be exported and persist in radically different places for millennia. Stated most straightforwardly, most of earth’s humans have inherited their beliefs about the nature of birth and death and everything in between and thereafter from preliterate Middle Eastern pastoralists.

  The second half of the chapter, just concluded, addresses the key issue of how we got here—has it been hundreds of thousands of years of Hobbes or of Rousseau? Your answer to that question greatly shapes what you’ll make of something we’ll consider in the final chapter, namely that over the last half millennium people have arguably gotten a lot less awful to one another.

  Ten

  The Evolution of Behavior

  At last we reach the foundations. Genes and promoters evolve. As do transcription factors, transposases, and splicing enzymes. As has every trait touched by genetic influences (i.e., everything). In the words of the geneticist Theodosius Dobzhansky, “Nothing in biology makes sense except in the light of evolution.” Including this book.1

  EVOLUTION 101

  Evolution rests on three steps: (a) certain biological traits are inherited by genetic means; (b) mutations and gene recombination produce variation in those traits; (c) some of those variants confer more “fitness” than others. Given those conditions, over time the frequency of more “fit” gene variants increases in a population.

  We start by trashing some common misconceptions.

  First, that evolution favors survival of the fittest. Instead evolution is about reproduction, passing on copies of genes. An organism living centuries but not reproducing is evolutionarily invisible.* The difference between survival and reproduction is shown with “antagonistic pleiotropy,” referring to traits that increase reproductive fitness early in life yet decrease life span. For example, primates’ prostates have high metabolic rates, enhancing sperm motility. Upside: enhanced fertility; downside: increased risk of prostate cancer. Antagonistic pleiotropy occurs dramatically in salmon, who epically journey to their spawning grounds to reproduce and then die. If evolution were about survival rather than passing on copies of genes, there’d be no antagonistic pleiotropy.2

  Another misconception is that evolution can select for preadaptations—neutral traits that prove useful in the future. This doesn’t happen; selection is for traits pertinent to the present. Related to this is the misconception that living species are somehow better adapted than extinct species. Instead, the latter were just as well adapted, until environmental conditions changed sufficiently to do them in; the same awaits us. Finally, there’s the misconception that evolution directionally selects for greater complexity. Yes, if once there were only single-celled organisms and there are multicellular ones now, average complexity has increased. Nonetheless, evolution doesn’t necessarily select for greater complexity—just consider bacteria decimating humans with some plague.

  The final misconception is that evolution is “just a theory.” I will boldly assume that readers who have gotten this far believe in evolution. Opponents inevitably bring up that irritating canard that evolution is unproven, because (following an unuseful convention in the field) it is a “theory” (like, say, germ theory). Evidence for the reality of evolution includes:

  Numerous examples where changing selective pressures have changed gene frequencies in populations within generations (e.g., bacteria evolving antibiotic resistance). Moreover, there are also examples (mostly insects, given their short generation times) of a species in the process of splitting into two.

  Voluminous fossil evidence of intermediate forms in numerous taxonomic lineages.

  Molecular evidence. We share ~98 percent of our genes with the other apes, ~96 percent with monkeys, ~75 percent with dogs, ~20 percent with fruit flies. This indicates that our last common ancestor with other apes lived more recently than our last common ancestor with monkeys, and so on.

  Geographic evidence. To use Richard Dawkins’s suggestion for dealing with a fundamentalist insisting that all species emerged in their current forms from Noah’s ark—how come all
thirty-seven species of lemurs that made landfall on Mt. Ararat in the Armenian highlands hiked over to Madagascar, none dying and leaving fossils in transit?

  Unintelligent design—oddities explained only by evolution. Why do whales and dolphins have vestigial leg bones? Because they descend from a four-legged terrestrial mammal. Why should we have arrector pili muscles in our skin that produce thoroughly useless gooseflesh? Because of our recent speciation from other apes whose arrector pili muscles were attached to hair, and whose hair stands up during emotional arousal.

  Enough. Don’t get me started.

  —

  Evolution sculpts the traits of an organism in two broad ways. “Sexual selection” selects for traits that attract members of the opposite sex, “natural selection” for traits that enhance the passing on of copies of genes through any other route—e.g., good health, foraging skills, predator avoidance.

  The two processes can work in opposition.3 For example, among wild sheep one gene influences the size of horns in males. One variant produces large horns, improving social dominance, a plus for sexual selection. The other produces small horns, which are metabolically cheaper, allowing males to live and mate (albeit at low rates) longer. Which wins—transient but major reproductive success, or persistent but minor success? An intermediate form.* Or consider male peacocks paying a price, in terms of natural selection, for their garish plumage—it costs a fortune metabolically to grow, restricts mobility, and is conspicuous to predators. But it sure boosts fitness via sexual selection.