The evolutionary origins of human nature

On this week's Science Saturday John Horgan interviews Richard Wrangham. The second half of the conversation focuses on Wrangham's new book, Catching Fire: How Cooking Made Us Human. I've heard pieces of the arguments mooted in the back & forth before, but it looks like in this book they're all brought together. Humans are a large animal with a very small gut, so we need to maximize the bang-for-the buck when it comes to what we eat. Unlike gorillas and to a lesser extent chimpanzees we just aren't able to process enough low quality vegetable matter to keep ourselves going. Part of this also might be due to the fact that we have some serious energetic needs, our outsized brains require a lot of energy to keep them chugging along (as anyone with low blood sugar can tell you), and I also recall that our bipedal locomotion isn't quite as efficient as that of the typical mammal's at high speeds. Due to the topic it's no surprise that they spend a fair time talking about the Raw Food movement. Wrangham's thesis that we're primed to consume cooked food because of our evolutionary background is obviously at odds with the theories which Raw Foodists propose (i.e., that in our "natural" state we didn't cook foods). This is similar to some vegetarians who assert that man is naturally a plant eater. The very fact that we tend to crave meat and cooked foods would tend to argue against that, but there is plenty of evidence that humans have been omnivores who used fire to preprocess their food for a long time. But, the very difficulty of consumption of raw foods, or a high vegetable diet, is probably what makes them often a good choice for someone who wants to lose weight in an affluent society. In world with a surfeit of nutritional intakes putting foods on your plate which are relatively hard to digest (high fiber, etc.) and have a lower caloric intake per unit is a way to modulate consumption naturally (taking advantage of the very unnaturalness of what one is consuming).

Despite the interesting data and theories in Wrangham's new book, I found the the first half of the discussion of more interest, as it focused on the ideas originally presented in Demonic Males: Apes and the Origins of Human Violence. I really can't reiterate how awesome I think this book is. Like The Blank Slate, Sociobiology and Guns, Germs, and Steel it is a narrative filled with many compelling arguments, and the power of its exposition is such that whether one accepts many of the assertions is besides the point. It changes how you view the whole question, and even if one dissents from the conclusion it serves as a reference against which one must formulate an argument. Like Wrangham I believe that some level of intergroup violence was probably the norm for most of human history. He disputes revisionist anthropologists who question the old consensus that hunter-gatherers are particularly prone to interpersonal and intergroup violence, but to me that is somewhat secondary consideration. Inter and intraspecific conflict and competition, and cooperation, are part of nature in most species.

The weights of these various parameters can vary, naturally. Humans are an extremely social species, but we have plenty of data that between group dynamics can lead to an eliminationist, or less ominously, assimilationist, conclusion. When societies are at the Malthusian limit the Four Horsemen make an appearance. When societies are not at the Malthusian limit, such as those groups which are the wave of demographic advance, between group dynamics may be less characterized by zero-sum thinking. Behavioral economists will tell you that the human default seems to be a zero-sum assumption, and this makes sense from a biological perspective as for most of history populations have not been on a wave of demographic advance (note that shifting from hunting & gathering to agriculture resulted in demographic expansion because the per unit amount of energy that humans could extract from an acre of land increased by orders of magnitude with agriculture, so groups were temporarily well below the new Malthusian limit). In the period after 1800 economic growth has been extremely fast in relation to the human norm, and this has resulted in sea change in expectations of standard of living, but nevertheless in most democratic societies the electorate exhibits a bias toward zero-sum assumption in terms of possibilities of wealth generation.

In any case as Wrangham notes it is wrongheaded to caricature his argument as genetically determinist as he acknowledges that there has been change over time. Steven Pinker's next book is presumably about the decline in violence from antiquity to the present. Even among the ancients there were shifts in the norm, the tale of Iphigenia in Greek mythology reflects the reality that human sacrifice was practiced during the Bronze and Dark Ages, but no longer during the Classical period. Though there might have been genetic changes in average personality type, the fluctuations over even short periods suggest that other dynamics are necessarily at play. Consider the relative peace of Europe in the 19th century in the wake of the Napoleonic Wars. Human institutions change and evolve and channel the basal biases of our nature. Short term variation in the nature of violence can be tracked to shifts in institutions or historical experiences. During the early phase of the wars in the wake of the French Revolution the armies of the Republic repelled invasions by other European powers. Though some scholars assumed this was a function of the élan of the citizen conscripts, quantitative historians have shown that one variable was an overwhelming predictor of which armies won: the number of men under arms.* The aristocratic monarchies of Europe had to match France's state under arms, which naturally resulted in even greater numbers of men killed as massive armies clashed. After the bloodletting the elites and populace of Europe had little taste for war, and the Age of Metternich commenced. During this period the propensity toward belligerence was put under leash by both humans and their institutions.

Explanation for why large scale societies vary in violence, and why there are secular trends in terms of the Zeitgeist, need not appeal to biology, but can accept basic biological imperatives and impulses which manifest in smaller scale societies where the institutional scaffold is less constraining. Behavior genetics tells us that even on the scale of individuals a great deal of life outcomes seem path dependent, or simply unpredictable, even for identical twins. Here you see that even with common genes and upbringing much is not determined. It seems strange to assume that basic impulses naturally must lead to a particular behavior outcome necessarily, and, that that outcome is somehow morally preferable. The irony is many who label others genetic determinists seem to be awfully skeptical of the power of human institutions to modulate the outcomes contingent upon a basic psychological template.

* Interestingly the same historians have calculated that the presence of Napoleon Bonaparte as the commanding general was worth 30% more troops!