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A Multi-Agent Systems Approach to Gossip and the Evolution of Language

A Multi-Agent Systems Approach to Gossip and the Evolution of Language Inge Slingerland (i.slingerland@student.rug.nl) 1 Maurice Mulder (mmulder@ai.rug.nl) 1 Elske van der Vaart (e.e.van.der.vaart@rug.nl) 1,2 Rineke Verbrugge (l.c.verbrugge@rug.nl) 1 Artificial Intelligence, University of Groningen, P.O. Box 407 9700 AK Groningen, the Netherlands Theoretical Biology, University of Groningen, P.O. Box 14 9750 AA Haren, the Netherlands Abstract In his book Grooming, Gossip and the Evolution of Language, biologist Robin Dunbar (1997) proposes a new way of looking at the evolution of language. According to this view, language evolved to provide a new social bonding mechanism: Gossiping. This allows humans to live in larger groups than other primates, which increasing predation risks forced our ancestors to do. We use a computational multi- agent model to test the internal workings of this hypothesis, with interesting results. Our work provides a fundamentally new kind of evidence for Dunbar’s theory, by experimentally demonstrating that greater group sizes can stimulate the evolution of language as a tool for social cohesion. Keywords: Evolution; language; multi-agent systems. Introduction As humans, we spend a great deal of time talking to each other. Most of this time is also spent talking about each other: Approximately 65% of our conversations focus on social topics (Dunbar, 2004). Given the amount of time we spend on all this gossip, it seems it must serve an important function. According to Robin Dunbar's (1997) theory of the evolution of language, it does: Gossip, he claims, is what allows humans to maintain social coherence in very large groups, and the selective pressure to do so is what drove us to evolve language in the first place. According to this theory, before humans learned to gossip, something else must have kept our groups together. The likeliest candidate is the mechanism still employed by other primates: Grooming. This keeps individuals clean, but it also serves an important social function. The exchange of grooming allows group hierarchies to be established and maintained, alliances to be formed, and apologies to be made (Seyfarth, 1977). For other primates, then, grooming is a very effective form of social glue. The only problem is that for groups comprising many individuals, grooming becomes a very time-intensive way of maintaining social bonds. As group size increases, so does the time primates invest in grooming (Dunbar, 2004). This is because larger group sizes create more ecological competition, as local food sources are more quickly exhausted. This creates fights, which makes effective alliances more important. But the effectiveness of an alliance directly depends on the time the members of that alliance devote to grooming each other (Dunbar, 2004). Of course, primates cannot groom all the time - they also need to eat and look for food. This means that there is an upper limit to the time that can be devoted to grooming, which, according to Dunbar (2004), is about 20% of an individual's waking hours. Consequently, there is a maximum group size in which it is possible to maintain sufficiently strong alliances by means of grooming. According to Dunbar (2004), this maximum group size is approximately 80 individuals. However, somewhere over the course of human history, increasing predation risks forced our ancestors to live in groups larger than that. Modern humans seem to have a natural group size of about 150, which is the typical size of most religious communities and military units (Dunbar, 1993). This figure is known as Dunbar's number, and also follows from his analysis of neocortex size (Dunbar, 1992). By looking at living primate groups, he has found a fixed relationship between the a primate species’ neocortex size and its group size. Dunbar concludes from this that neocortex size determines how many social contacts one can maintain. By extrapolating this measured relationship to humans, the same maximum group size of 150 individuals appears (Dunbar, 1993). However, like other primates, we only spend about 20% of our time on social activities (Dunbar, 2004). Therefore, our social bonding mechanism must be more effective than grooming is. Gossip, or talking about social topics, fits the bill. Like grooming, it is a social activity that allows us to display selective interest in other individuals, strengthening relationships. But it also has a number of advantages over grooming: It can involve more than two participants at once, and it allows individuals to exchange social information, so they can learn about events they did not see themselves (Dunbar, 2004). In short, gossiping makes maintaining of social bonds much more efficient. But gossip also has disadvantages, the primary one being that it is less intimate. The physical aspects of grooming release endorphins, and when people want to share deep feelings and emotions with each other, they tend to do it by touching, rather than talking (Dunbar, 2004). According to Dunbar’s hypothesis, then, at some point in our evolutionary history, we traded much of the intimacy of grooming for the efficiency of gossip, which was necessary to allow our ancestors to live in larger groups. In essence, humans evolved language and large neocortices to be able to talk about each other.