Bruce Hood - The Domesticated Brain - A Pelican Introduction (Pelican Books)

Homo psychologicus – the social brain hypothesis

Evolutionary psychologist Robin Dunbar at Oxford University has argued that humans evolved large brains to enable them to live in large social groups. 30Domestication in recent human history may have triggered a reduction in brain size over the last 20,000 years, but brains had to initially grow larger during the much longer extent of hominid evolution over the past 2.5 million years in order to live in social groups. This idea, known as the social brain hypothesis , argues that communal living required the development of large brains to navigate the social landscape but not all animals that live in large groups have particularly big brains. If that were so, we would expect the wildebeest that migrate in vast numbers across the plains of Africa to be particularly cerebrally well endowed – which they are not. They form large herds but they are not organized and coordinated by complicated social relationships. So merely living as part of a social group does not adequately explain the increased size of brains. Rather, you have to look at the nature of the social interaction of animals that live in groups to understand why big brains confer social adaptation.

UCLA anthropologist Joan Silk has studied the social organizations of different apes and monkeys and thinks that it is the ability to recognize the relationships between other members, or ‘third-party knowledge’ – a sort-of ‘he knows that she knows’ type of understanding – that is the critical skill for living in social groups. 31Many primates are sensitive to such third-party knowledge. Upon hearing the distress call of an infant monkey, wild vervet monkeys hidden in the bushes will turn towards the mother and the direction of the call, which shows they recognize the mother–infant relationship. In chimpanzees, males form dominance hierarchies that confer all the advantages of fathering more offspring. These chimp gangs are based on allegiances formed by pretenders to the throne who recruit followers through social interactions in much the same way individuals form gangs to rule the school playground. Once in place, the new top boss or ‘alpha male’ has the pick of the females, but he will tolerate attempts to mate from those who helped him establish the new regime.

If today’s non-human primates engage their social skills for power struggles, then it is likely that early hominids did the same. To support his social brain hypothesis, Dunbar analysed the relative brain size of many different animals and discovered that those with proportionately the largest brains are the ones that live in larger structured groups and possess more social skills. Primates in these groups have a larger repertoire of calls that enable them to communicate more complex information, a feat that requires larger brains. 32

This relationship between brain size and social behaviour is found throughout the animal kingdom. It is not only true for social animals such as elephants but also sea-dwelling mammals such as dolphins and whales. It is also true in the bird world. A good case in point is the Corvidae family of crows, jays and magpies. Caledonian crows have bigger brains than the larger chicken and not surprisingly they are also considerably smarter. In fact, when faced with puzzles that are suitable for birds, Caledonian crows outperform many primates, which is why they have been called feathered apes. 33

Longer childhoods are another feature of social animals who invest time raising their young. A chicken is independent by four months after birth and reaches maturity by six months, whereas Caledonian crows are still fledgelings at two years and require continual feeding from the parents. This is why corvid parents pair-bond for life, because it is an evolutionary strategy for sharing the responsibility of raising offspring that take so long to mature. Bigger brains may provide these animals with more flexibility in their problem solving, but they need it to be able to provide for their demanding kids.

Cultural explosion

When our species appeared on the scene some 200,000 years ago in Africa, Homo sapiens lived in organized social groups, communicating through gesture and simple language to enable them to cooperate and coordinate. We know this because the ancestor to both Homo sapiens and Homo neanderthalensis, Homo heidelbergensis, who had been around for maybe as long as 1.3 million years, was already a skilled hunter. In Schöningen, Germany between 1994 and 1998, eight exquisitely fashioned wooden throwing spears measuring 2 metres long were found among the skeletons of twenty horses. They were carved so that the weight was towards the front of the spear, making it fly straighter, similar to the design of a modern javelin. As a boy scout, I unsuccessfully tried to make spears and I doubt many of us today would know what the optimum design is. The Schöningen spears date to around 400,000 years ago, proving that Homo heidelbergensis was sophisticated enough to make a weapon sufficiently lethal to bring down a larger animal. This technological advance could not have suddenly appeared but rather must have been passed on through social learning. Since horses are difficult to corner, a hunting party would be needed to coordinate the attack, suggesting they had the ability to communicate. Given their expert skills in hunting horses, Homo heidelbergensis proves that culture was already present before the appearance of Homo sapiens 200,000 years ago. 34

Soon after the appearance of Homo sapiens , other examples of social learning and culture began to show up in the fossil record. Samples of haematite, a red iron oxide that can be used as pigment for body adornment, have been found in Zambian sites dating to around 160,000 years ago. Ceremonial burials including a man clutching the jawbone of a wild boar have been dated to around 115,000 years. Other graves of the same period contained beads. Why go to this effort unless there was some symbolic meaning for the objects?

As they rapidly spread geographically across the planet, Homo sapiens must have been equipped with a brain capable of much more culture than ever seen before. Based on a statistical analysis of the global data set of mtDNA sequences, it is believed that there was an increase in the Homo sapiens population around 100,000 years ago that would have produced a demographic that was ripe for enabling culture to flourish through the exchange of ideas and migrations of individuals. 35

From around 100,000 to 45,000 years ago, there had been sporadic examples of cultural practices such as ceremonial burials and symbolic behaviour like art and body decoration. However, in Europe around 45,000 years ago, Homo sapiens became anatomically modern humans engaging in all the trappings of primitive civilization. They were as close to us today as we can find in terms of their bodies. They also behaved much more like us than any other ancestor. Around this time there was a cultural explosion as evidenced by the advances in tool technology, elaborate jewellery, symbolic sculptures, cave paintings, musical instruments, talismans and the spread of religious ceremonies and burials. 36Each of these activities was undertaken for a purpose that required a level of social interaction far in excess of anything seen before or remotely present in the animal kingdom. Humans had clearly begun to trade, as many of the raw materials for the artefacts had been transported great distances. In other words, we were already becoming vain. Art and jewellery are primarily made to be seen and admired by others. Making jewellery and creating art took considerable time and effort and would only have been undertaken and appreciated for the social value such activities conveyed. Burials and religious ceremony reflect an awareness of death and thoughts about the afterlife and creators. It may be true that some primates show the behavioural signs of mourning their dead, but modern humans are the only species that engage in death rituals.