Egalitarian revolution in the Pleistocene?

Also increasing were the abilities to keep track of within-group social interactions, to remember friends and their allies and enemies, and to attract and use allies. At some point, physically weaker members of the group started forming successful and stable large coalitions against strong individuals who otherwise would achieve alpha-status and usurp the majority of the crucial resources. Eventually, an egalitarian society was established. Although some of its components are well supported by data, this scenario remains highly controversial. One reason is its complexity which makes it difficult to interpret the data and to intuit the consequences of interactions between multiple evolutionary, ecological, behavioral, and social factors acting simultaneously. It is also tricky to evaluate relevant time-scales and figure out possible evolutionary dynamics.

A paper published in PLoS ONE today makes steps towards answering these challenges. The paper is co-authored by Sergey Gavrilets, a theoretical evolutionary biologist, and two computer scientists, Edgar Duenez-Guzman and Michael Vose, all from the University of Tennessee, Knoxville.

The researchers built a complex mathematical model describing the process of alliance formation which they then studied using analytical methods and large-scale numerical simulations. The model focuses on a group of individuals who vary strongly in their fighting abilities. If all conflicts were exclusively between pairs of individuals, a hierarchy would emerge with a few strongest individuals getting most of the resource. However, there is also a tendency (very small initially) for individuals to interfere in an ongoing dyadic conflict thus biasing its outcome one way or another. Positive outcomes of such interferences increase the affinities between individuals while negative outcomes decrease them. Naturally, larger coalitions have higher probability of winning a conflict.

Gavrilets and colleagues identified conditions under which alliances can emerge in the group: increasing group size, growing awareness of ongoing conflicts, better abilities in attracting allies and building complex coalitions, and better memories of past events.

Most interestingly, the model shows that the shift from a group with no alliances to one or more alliances typically occurs suddenly, within several generations, in a phase-transition like fashion. Even more surprisingly, under certain conditions (which include some cultural inheritance of social networks) a single alliance comprising all members of the group can emerge in which resources are divided evenly. That is, the competition among non-equal individuals can paradoxically result in their eventual equality.