Brain Size and Egalitarianism
Discussion
Camilla Power:
"The most salient feature of our anatomy distinguishing us from other apes is the extraordinary size of our brains. While a human and chimp mother have a fairly similar body weight, adult humans today have upwards of three times the brain volume of a chimp. Brain tissue is very expensive in terms of energy requirements. Doing the whole job by themselves, great ape mothers are constrained in the amount of energy they can provide to offspring and so apes cannot expand brains above what is known as a ‘gray ceiling’ (600 cc). Our ancestors smashed through this ceiling some 1.5-2 million years ago with the emergence of Homo erectus, who had brains more than twice the volume of chimps today. This tells us that cooperative childcare was already part of Homo erectus society, with concomitant features of evolving cooperative eyes and emergent intersubjectivity.
We can really track the degree of egalitarianism in the societies of descendants of Homo erectus, by measuring the size of brains in these early humans, using the fossil record. From 6-700,000 years ago we begin to see cranial values in the modern human range, three times as large as present day chimps. From half a million years ago, for both African (modern human ancestor) and Eurasian (Neanderthal ancestor) populations, an extraordinary acceleration of brain size is seen. What we find evidenced in the fossil record is materially more energy for females and their offspring. This implies an inevitable gendering of the strategies that enabled this to happen.
Any tendency to male dominance, sexual competition and strategic control of females would have obstructed these unprecedented increases of brain size. While there must have been variability in the degree of dominance or egalitarianism among human groups, we can be confident that those populations where male dominance, sexual conflict and infanticide risks remained high were not the ones who became our ancestors. Our forebears were the ones who somehow solved the problem of great ape male dominance, instead harnessing males into routine support of these extraordinarily large-brained offspring.
One key question is what actually drove the increase of brain size. Brains are wonderful to have if you can afford them. But such large increases of brain size are vanishingly rare in evolution because of the expense. What are these large brains for? One major hypothesis is the Social Brain theory. This relates brain size, specifically the size of the neocortex, across primate species, to the degree of social complexity, the network of relationships that any individual needs to deal with. This can be measured by average group sizes for any particular species, or sizes of coalitions and cliques within social groups. One version of the ‘social brain’ focuses on specifically female group sizes as most critical in driving the evolution of intelligence.
The original idea behind social brain was called Machiavellian Intelligence. Arising in the late 1980s, this switched the focus of understanding the evolution of intelligence from technology and foraging to social relationships. Machiavellian intelligence is a subtle idea that sees animals in complex social groups competing in evolutionary terms by becoming more adept at cooperation, and more capable of negotiating alliances. In this theoretical perspective, then, the significant increases of brain size in the primate order, from monkeys to apes, and then from apes to hominins, result from increasing political complexity and ability to create alliances.
Egalitarianism is difficult to explain using Darwinian theory premised on competition. Andrew Whiten, one of the inventors of Machiavellian intelligence theory, and his student David Erdal saw that Machiavellian intelligence could generate the difference between primate-style dominance hierarchies and typical hunter-gatherer egalitarianism. At a certain point, the ability to operate within alliances exceeds the ability of any single individual, no matter how strong, to dominate others. If the dominant tries, he (assuming ‘he’ for the moment) will meet an alliance in resistance who together can deal with him. Once that point is reached, the sensible strategy becomes not to try to dominate others, but to use alliances to resist being dominated oneself. This was termed ‘counterdominance’ by Erdal and Whiten, and they used it to describe what is found regularly in African hunter-gatherer societies, so-called demand-sharing, an attitude of ‘don’t mess with me’, humour as a levelling device, and the impossibility of coercion since no particular individual is in charge. They saw counterdominance as fundamental to the evolution of human psychology, with competing tendencies for individuals to try to get away with bigger shares where opportunity presents, but, faced with demands from others, to give in and settle for equal shares.
Whiten and Erdal focused on food-sharing as the most visible aspect of hunter-gatherer egalitarianism. But how does sex fit into this model? Whiten and Erdal noted the general hunter-gatherer tendency for monogamy, or serial monogamy, which contrasts with polygyny among propertied farmers and herders. But again we need to go to our biology to see the underlying features of our reproductive physiology that lead to reproductive egalitarianism – the most significant form of egalitarianism from an evolutionary perspective.
Women have evolved a sexual physiology which can be described as levelling and time-wasting. Why? Because if a hominin female really needs extra energy for her hungry offspring, better to give reproductive rewards to males who will hang around and do something useful for those offspring. Our reproductive signals make life hard for males who want to identify fertile females, monopolise the fertile moment and then move on to the next one (a classic strategy for dominant male apes). We have concealed and unpredictable ovulation. A man cannot really tell when his partner is ovulating, and women appear to confuse the issue with all kinds of biochemical signals. On top of that, women are sexually receptive, potentially, for virtually all of their cycle, a much larger proportion than any other primate. The combined effect is to scramble the information for males about exactly when a female is fertile.
From the viewpoint of a dominant male trying to manage a harem of females this is disastrous. While he is guessing about the possible fertility of one cycling female, he has to stay with her, and is missing other opportunities. Meanwhile, other males will be attending to those other sexually receptive females. Continuous sexual receptivity spreads the reproductive opportunities around many males, hence is levelling from an evolutionary perspective.
BaYaka women of the Congo forest have a slogan perfectly expressing their resistance to male philandering: ‘One woman, one penis!’ This serves as their ritual rallying cry against any attempt by a man to form a harem. Basically, hunter-gatherer women are demanding one man each to support their energy requirements and investment in costly offspring.
In farming and herding societies, some men may be able to muster resources, large livestock or land, enabling them to acquire more than one wife, those wives and their children then forming the patriarch’s labour force. This automatically means other men are going without reproductive opportunities. But for immediate-return hunter-gatherers, those who consume all they hunt and gather the same day, men cannot accumulate resources and harem-holding is simply not stable."