The dynamics of Machiavellian intelligence

Abstract

The "Machiavellian intelligence" hypothesis (or the "social brain" hypothesis) posits that large brains and distinctive cognitive abilities of humans have evolved via intense social competition in which social competitors developed increasingly sophisticated "Machiavellian" strategies as a means to achieve higher social and reproductive success. Here we build a mathematical model aiming to explore this hypothesis. In the model, genes control brains which invent and learn strategies (memes) which are used by males to gain advantage in competition for mates. We show that the dynamics of intelligence has three distinct phases. During the dormant phase only newly invented memes are present in the population. During the cognitive explosion phase the population's meme count and the learning ability, cerebral capacity (controlling the number of different memes that the brain can learn and use), and Machiavellian fitness of individuals increase in a runaway fashion. During the saturation phase natural selection resulting from the costs of having large brains checks further increases in cognitive abilities. Overall, our results suggest that the mechanisms underlying the "Machiavellian intelligence" hypothesis can indeed result in the evolution of significant cognitive abilities on the time scale of 10 to 20 thousand generations. We show that cerebral capacity evolves faster and to a larger degree than learning ability. Our model suggests that there may be a tendency toward a reduction in cognitive abilities (driven by the costs of having a large brain) as the reproductive advantage of having a large brain decreases and the exposure to memes increases in modern societies.

Fig. 1.

The dynamics of the number of unique memes (a), the average learning ability (b), the average cerebral capacity (c), and the average Machiavellian fitness (d) in 20 runs with a default set of parameter values (L = 16, K = 100, c_max = 32, f_max = 10, ρ = 0.5).

Fig. 2.

The median time to cognitive explosion with ρ = 0.5.

Fig. 3.

The dynamics of the learning ability a (solid line), normalized cerebral capacity c/c_max (dashed-dot line), and viability v (dashed line) averaged over 20 runs shown in Fig. 1.

Fig. 4.

The characteristics of the population 8,000 generations after the cognitive explosion. (a) The average learning ability. (b) The average cerebral capacity. (c) The average Machiavellian fitness. (d) The average number of memes per individual. ρ = 0.5.