IN THE TWENTIETH CENTURY, a handful of anthropologists, living with hunter-gatherers, described the workings of societies without leaders, where food seemed to be equally available to all. 
These reports resonated with Rousseau’s visions of primitive equality and Marxist theories about the deep roots of communism. 
Could hunter-gatherers be seen as “living fossils,” showing us how we all once lived — and might one day live again?
In the past decades a lot of new work has been done that is relevant to these questions.
Nobody now believes that modern hunter-gatherers are typical of our way of life in the Palaeolithic. But there’s broad agreement that they can shed light on ancestral conditions — that they’re the best analogue we have. 
While memory of the Conference on Hunting and Gathering Societies is still fresh, I’ll share some current thinking on political organization among hunter-gatherers — particularly the question of how egalitarianism might have evolved.
The egalitarianism papers
In Liverpool there were two presentations on hunter-gatherer egalitarianism — one by Frank Marlowe of Cambridge, and one by me.
Marlowe, using a carefully drawn sample of cultures, showed that lack of social stratification is more common among hunter-gatherers than in societies relying on other types of subsistence (farmers, horticulturalists, or pastoralists).
And among hunter-gatherer populations, those with higher rates of mobility and greater reliance on large game for their diet are less likely to have social stratification.
In other words, while not all hunter-gatherers are egalitarian, those who are, tend often to be mobile and rely on big game.
How typical these features were of our ancestors is a point of contention (to which we’ll return).
In my presentation, I focused on the possible origins of egalitarianism.
Proximate versus ultimate causation
Work on the evolution of egalitarianism, I suggested, might profit from observing a distinction that biologists often make between forces that could select for a behavior and forces that could maintain it once it emerged.
Taking bird migration as an example, the forces that could lead birds in the northern hemisphere to migrate south during winter include genetic disposition and lack of food (ultimate causes), and physiological responses to falling temperature and shorter days (proximate causes). 
Only the “ultimate” forces, it’s generally agreed, could cause the behavior to evolve by natural selection.
In the case of egalitarianism, ultimate mechanisms would cause differential survival in hierarchical versus non-hierarchical groups; and proximate mechanisms would include various ways of keeping the playing field level — for example by knocking down aggrandizers.
Some mechanisms that might account for the evolution of egalitarianism are kin selection (favouring your kin, which could promote egalitarianism if relatedness within the group were high), reciprocity (trading of favours), assortment (associating only with others who had proven themselves in the past), and group selection (treating group members as equals, and competing together against other groups).
Some of these ideas can be eliminated quickly. Kin selection, for example, doesn’t square with what we know about hunter-gatherer band composition. (Band membership tends to be diverse and fluid, and kin biases would be hard to maintain. ) But others are more difficult to evaluate.
Computer simulation seems to be a promising way of investigating how ideas such as these stand up in relation to one another.
Dispensing with all but the most basic features of social life, agent-based models make it possible to investigate the emergence of complex social phenomena from relatively simple rules of social interaction. 
A model created by Gavrilets, for example, begins with “bullies” attempting to steal food from others (a common enough occurrence in primate societies). The model demonstrates how, when other group members intervene to defend the weak from bullying, a social norm of fairness can emerge, and this in turn can lead to a stable mode of egalitarianism.
The challenge remains to integrate models with real-world data — to let the virtual and actual worlds speak to each other.
Not long ago, you had to have specialized training to develop and run computer simulations. But within the last decade, off-the-shelf simulation packages have proliferated, and it’s now possible for anyone with even basic computer literacy to experiment with agent-based modeling, for example with NetLogo.
The presentations generated a lively discussion.
Chris Knight took issue with our lack of attention to gender relations.
How could we attempt to understand egalitarianism without taking relations between men and women into account? he asked.
And Ian Watts asked on what grounds I was calling leveling mechanisms a “proximate” force in the evolution of egalitarianism.
Couldn’t they be a primary force in pushing groups towards egalitarian modes?
These questions stimulated me to think about this problem in a new way.
Reading further on the ultimate/proximate distinction, I realized that something of a revolution is underway in how evolutionary biologists are thinking about causation.
Back in the 1970s, Stephen Jay Gould devoted a book to the history of inquiry into the relationship between evolution and life-course development, showing how the topic has been an enduring source of controversy. 
The most recent cycle of work in this area has led to a rethinking of the ultimate / proximate distinction. 
One of the frame-shifts that this has brought about relates to the idea of the nuclear family versus the extended group as the locus of child rearing.
Hunter-gatherers rely heavily on other members of their groups to share care of offspring, and their kinship and marriage systems seem designed to maximize the availability of helpers. 
Networks of support may be spread wider still by cultivating friendships (think of godparents) — what are sometimes called “social kin.” 
Sarah B. Hrdy’s hypothesis is that
“Novel rearing conditions among a line of early hominins meant that youngsters grew up depending on a wider range of caretakers … and this dependence produced selection pressures that favored individuals who were better at decoding the mental states of others, and figuring out who would help and who would hurt.” 
This ability to read others’ minds and intentions — part of what Hrdy calls “emotional modernity” — would facilitate shared child care; and once care was widely enough distributed, the reproductive success of individuals could begin to be favoured by egalitarian arrangements.
This scenario opens the door to gender relations as a prime mover in the evolution of egalitarianism, as it implies a shift from a situation where mothers bore sole responsibility for child care, to one where others, including men, shared it.
At the same time, the overturning of the proximate/ultimate distinction also makes other hypotheses seem more plausible, for example the idea that being generous with food, and refraining from self-aggrandizement, could be a means of indicating an individual’s fitness (a “costly signal”). 
As the number of competing hypotheses grows, one may start to wonder whether there’s any hope of resolving the question of how egalitarianism might have evolved.
At least three lessons, however, emerge from all this for me:
First, there is no reason to suppose that egalitarianism should have evolved by the same mechanism everywhere.
Like birds and bats, which made similar-looking wings out of very different starting materials, different human groups may have arrived at egalitarian arrangements by different routes.
Working out which mechanisms were most important for different groups, at different times, requires attention to some of the key variables that scholars have identified, for example the importance of big game hunting and degrees of mobility.
Second, we need not assume that hunter-gatherers in the distant past were always egalitarian.
It could be, instead, that we have an ability to shift into egalitarian mode under conditions that favour it — we might be facultative or “fair weather” egalitarians. 
Third, cultural evolution opens up a wide range of possibilities for the emergence of egalitarianism.
While birds migrating south for the winter may be locked into their behavior patterns by genetic control, human culture permits great flexibility.
Acknowledging that “our species is free neither of itself nor its environment,”  the overlay of cultural processes in humans nonetheless creates the possibility of conscious, directional change in political organization.
There’s reason, in other words, for hope that we’re predestined neither for communism nor for tyranny.
 e.g. the Mbuti of the Congo and the Hadza of Tanzania. Mbuti: Turnbull, Colin. 1961. The Forest People. Simon and Schuster; Hadza: Woodburn, James. 1982. ‘Egalitarian Societies’. Man 17 (3) (September 1): 431–451. doi:10.2307/2801707.
 Speth puts it well: “Modern foragers, whether they are isolated and autonomous or not, must nevertheless confront and cope with demographic, social, dietary, and other problems that are common to any human society, past or present, that relies for part or all of its sustenance on wild plant and animal foods.” (J.D. Speth, 1991. In Foragers in Context: Long-term, Regional, and Historical Perspectives in Hunter-gatherer Studies (Vol. 10). Ann Arbor: Department of Anthropology, University of Michigan, p. viii)
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 Hrdy, 2009. Mothers and Others, p. 66
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 This idea of oscillation between egalitarian and hierarchical social structures was suggested by James Woodburn.
 Lancaster, Jane B. 1975. Primate behavior and the emergence of human culture. Fort Worth: Holt, Rinehart, and Winston, p. 1