The evolution of the human brain in comparison with the rest of animals, specifically with primates, is still a mystery that is constantly being investigated. It has given rise to numerous debates since the English naturalist Charles Darwin presented his theory of evolution to the world in 1859.

One of the assumptions with more weight that try to explain this difference is the theory of Machiavellian intelligence, which relates the evolution and development of the brain with the level of social development of each species.

What is the theory of Machiavellian intelligence?

Unlike other animals, human beings have experienced infinitely superior brain development, with the cognitive and behavioural consequences that this entails. Even in comparison with primates, the human brain is considerably larger and more complex .

Although it has not yet been possible to establish with complete certainty what is the cause of these abysmal differences in brain development, there are many theories that attempt to explain this phenomenon that gave “homo sapiens” the ability to develop a much more complex mind.

Some of them propose that brain development is a response to the capacity to adapt to changes or alterations in the environment. According to these hypotheses, subjects with a greater capacity for adaptation and who were able to overcome and survive the adversities of the environment, such as environmental or meteorological conditions, have managed to disseminate their genes, giving rise to progressive brain development .

However, there is another theory with much more support from the scientific community: the theory of Machiavellian intelligence. Also known as the social brain theory, this assumption postulates that the most important factor in brain development is social competition.

Broadly speaking, this means that those individuals with more skills for life in society were more likely to survive. Specifically, these skills, which are considered to be Machiavellian, refer to social behaviors such as the ability to lie, mischief, and insight. That is, the most astute subjects with more social skills achieved much greater social and reproductive success.

How was this idea forged?

In the research work “Social behaviour and evolution of primates” published in 1953 by the researchers M. R. A. Chance and A. P. Mead, it was first suggested that social interaction, understood as part of an environment of competition for status within a social structure , could be the key to understanding brain development in hominid primates.

Later, in 1982, the Dutch researcher specialized in psychology, primatology and ethology Francis de Waal, introduced the concept of Machiavellian intelligence in his work Chimpanzee politics , in which he describes the social and political behaviour of chimpanzees.

However, it was not until 1988 that the theory of Machiavellian intelligence as such was developed. Thanks to the background that links the concepts of brain and social cognition and Machiavellian intelligence, psychologists Richard W. Byrne and Andrew Whiten, researchers at the University of St. Andrews in Scotland, have produced a compendium of research published under the name “Machiavellian intelligence: social experience and evolution of the intellect in monkeys, apes and humans”.

In this work the researchers present the hypotheses of Machiavellian intelligence, which tries to transmit the idea that the mere need to be more perceptive and astute than the rest of the individuals generates an evolutionary dynamic in which Machiavellian intelligence, in the form of the use of social cognition skills, would give rise to a social and reproductive advantage .


Brain development and social intelligence

Although at first glance it may seem complicated to associate the level of intelligence or brain development with a phenomenon of a social nature, the truth is that the hypothesis of Machiavellian intelligence is supported by neuroanatomical evidence .

According to this theory, the cognitive demands and requirements due to an increase in social interactions, which in turn comes from the gradual increase in the number of individuals in a society, caused an increase in the size of the neocortex, as well as in its complexity.

From the perspective of the hypothesis of Machiavellian intelligence, the increase of the complexity and size of the neocortex is a function of the variability of the behaviours that the subject can carry out in interaction with his society. This specification is especially relevant since it explains the differences in the development of the neocortex between primates and humans in comparison with other animal species.

Furthermore, numerous works and studies support the idea that the dimensions of the neocortex increase as the size of the social group increases . Furthermore, in the specific case of primates, the size of the amygdala, an organ traditionally linked to emotional responses, also increases as the size of the social group increases.

This is because for social integration and success it is necessary to correctly develop the skills of modulation and emotional regulation, hence the consequent increase in the size of the amygdala.

The study of Gavrilets and Vose

In order to test this hypothesis, the researchers from the University of Tennessee, United States, S. Gavrilets and A. Vose carried out a study in which by designing a mathematical model, the development of the brain of people could be simulated based on the theory of Machiavellian intelligence.

To do this, the researchers took into consideration the genes responsible for learning social skills . They concluded that the cognitive abilities of our ancestors increased significantly over only 10,000 or 20,000 generations, a very short time span considering the history of mankind.

This study describes brain and cognitive development in three different phases that occurred throughout human history:

  • First phase: the social strategies created were not transmitted from individual to individual.
  • Second phase: known as the “cognitive explosion” phase , in which a high point in the transmission of knowledge and social skills was manifested. It was the moment of greatest brain development.
  • Third phase: called the “saturation” phase . Due to the enormous expenditure of energy involved in maintaining an increasingly large brain, its growth was stopped, remaining as we know it today.

It is necessary to specify that the authors themselves report that their results do not necessarily prove the hypothesis of the theory of Machiavellian intelligence, but rather that the mechanisms or phenomena that produced this growth may coincide with the historical temporal moment in which it is hypothesized that they occurred.