Intelligence is notoriously difficult to define, however most experts agree that it is the ability to adapt and function effectively within a given environment. This definition is broad, and also allows us to consider that other animals posses “intelligence”.

Ecological explanations for human intelligence

Compared with other animals, primates in general have larger brains, and in order for us to fully understand human intelligence, we must first ask why the primate we have evolved from started off with such large brains?

Ecological explanations suggest that solving the problems of efficient foraging led to an increase in brain size. Evidence from fossils tell us that early primates were arboreal (tree living) and frugivorous (fruit eaters), and so solving the issues that come attached to having to move within their environment lead to larger and more cognitively evolved brains. Richard Byrne stated that early primates were effective at producing detailed cognitive maps as a result of this need to forage for food.

Around 14 million years ago, equatorial Africa began to shrink, opening up vast grasslands and savannahs. Consequently our ancestors had to begin to explore a wider range of food substances like meat. Whether the primates were “elbowed out” of the jungle environment by competitors, or whether they were better able to move on land than other species is strongly debated, however regardless of which event occurred, this change played a crucial role in human evolution

Then around 6 million years ago the common ancestor of humans and the chimpanzee split. The chimpanzees remained as they were, and the others became fully adapted to living in open plains. Becoming more fully adapted meant becoming:

• More upright
• More cooperative

Both in order to fashion tools and engage in group hunting.

The main premise of this explanation is that the evolution of human intelligence consists of two stages, the demand for foraging and the demand for hunting, both of which provided the problems that natural selection solved via creating a bigger, more intelligent brain.

Social complexity explanations for human intelligence

There are various different hypotheses surrounding this concept, however all of they agree on the key idea that predicting and dealing with the behaviour of others in a social group is the primary cause of our increased level of intelligence.

Nick Humphrey was the first to introduce this idea. He suggested that the most intelligent species (dolphins, chimpanzees, elephants) are, almost invariably, the most social. So it is not the problems of the physical environment but social ones that caused the evolution of intelligence.

This idea was developed by Richard Byrne and Andy Whitten, who composed the Machiavellian intelligence hypothesis. This hypothesis said that individuals can best achieve their own aims by predicting and manipulating the people they encounter. This supported the claim that the driving force for a large intelligent brain is the ability to read the minds of other people in the group and use this information to your advantage. The most important feature of this hypothesis is the ability to “impute states of minds to others”. In context, when we tell the truth, we simply report the facts of how things are. However to deceive and lie, we must first be able to work out what the other person is thinking. So once we possess the ability to glean insight into another person’s mind, we will have an advantage in being able to predict the actions of others, be it hostile or friendly.

Overall the social explanation of intelligence defines it as our ability to predict the actions or mind sets of other people. Evolution in this sense is not about getting nicer, but is about winning the competition in order to pass genes on, which is why the more social animals have become more intelligent and have effectively won the competition over the years to the point where humans have evolved to become a dominant species.

The function of the neo-cortex

The social explanation also has scientific evidence regarding the neo-cortex, the outer layer of the brain. Robin Dunbar observed primates and noted that the increase in brain size compared to other mammals is largely down to an increase in the size of the neo-cortex. He established that:

• The larger the social groups of primates, the more time they spend grooming each other
• The larger the social group, the larger the neo-cortex

Putting these facts together, Dunbar suggested that grooming helps to maintain social bonds, and a larger neo-cortex is essential to recognising individuals and interacting with them in a large social group.

It is worth noting that the neo-cortex is the part of our brain that deals with higher functions such as decision making and predicting the outcome of our actions – in other words this is the part of our brain responsible for our intelligence

So on this basis we can see that the more social animals such as dolphins or elephants become more intelligent as a result of the development of the neo-cortex, which is needed for them to recognise and interact with individuals in their larger social groups. This supports the social explanation for the evolution of human intelligence, and its scientific validity means this hypothesis is strongly supported.