Wednesday, April 22, 2009

Understanding the "Egalitarian Revolution" in human social evolution

Inspired by the previous bloggpost, here is some other news about a recent publication in this research laboratory. In the lastest issue of Trends in Ecology & Evolution I have a so-called Research Update about a recently published model by theoretical evolutionary biologist Sergey Gavrilets and colleagues which deals with the evolution of cooperation in humans. One striking aspect of humans that makes us different from our closest relatives, the great apes, is that our society is less hierarchical and hence more egalitarian, and the evolutionary transition from a great ape society to ours is something that took place during the Pleiostocene and this transition is often called "The Egalitarian Revolution".

The TREE-article comments uponGavrilets et als' new model that aims to explain this evolutionary transition, as well as some recent experimental studies by behavioural economist Ernst Fehr who have done some elegant work on human cooperation and "altruistic punishment". Here is the Abstract for my TREE-article:

"Humans are unique among animals in cooperating in large groups of unrelated individuals, with a high degree of resource sharing. These features challenge traditional evolutionary theories built on kin selection or reciprocity. A recent theoretical model by Gavrilets and colleagues takes a fresh look at the ‘egalitarian revolution’ that separates humans from our closest relatives, the great apes. The model suggests that information from within-group conflicts leads to the emergence of cooperative alliances and social networks."

One of the original articles discussed in this TREE-paper, the model by Sergey Gavrilets et al., was originally published in PLoS ONE, under the title "Dynamics of alliance formation and the Egalitarian Revolution." I had the pleasure of being an academic editor of this highly interesting piece of work. Here is the abstract for that paper:


Arguably the most influential force in human history is the formation of social coalitions and alliances (i.e., long-lasting coalitions) and their impact on individual power. Understanding the dynamics of alliance formation and its consequences for biological, social, and cultural evolution is a formidable theoretical challenge. In most great ape species, coalitions occur at individual and group levels and among both kin and non-kin. Nonetheless, ape societies remain essentially hierarchical, and coalitions rarely weaken social inequality. In contrast, human hunter-gatherers show a remarkable tendency to egalitarianism, and human coalitions and alliances occur not only among individuals and groups, but also among groups of groups. These observations suggest that the evolutionary dynamics of human coalitions can only be understood in the context of social networks and cognitive evolution.

Methodology/Principal Findings

Here, we develop a stochastic model describing the emergence of networks of allies resulting from within-group competition for status or mates between individuals utilizing dyadic information. The model shows that alliances often emerge in a phase transition-like fashion if the group size, awareness, aggressiveness, and persuasiveness of individuals are large and the decay rate of individual affinities is small. With cultural inheritance of social networks, a single leveling alliance including all group members can emerge in several generations.


We propose a simple and flexible theoretical approach for studying the dynamics of alliance emergence applicable where game-theoretic methods are not practical. Our approach is both scalable and expandable. It is scalable in that it can be generalized to larger groups, or groups of groups. It is expandable in that it allows for inclusion of additional factors such as behavioral, genetic, social, and cultural features. Our results suggest that a rapid transition from a hierarchical society of great apes to an egalitarian society of hunter-gatherers (often referred to as “egalitarian revolution”) could indeed follow an increase in human cognitive abilities. The establishment of stable group-wide egalitarian alliances creates conditions promoting the origin of cultural norms favoring the group interests over those of individuals.


  1. I am Alex Hermitage and I love Barry Nervous!

  2. Fuck off Barry Nervous!