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

Assisted childbirth could have been an early behaviour that fostered the right conditions for compassion, altruism, trust and other social exchanges that would become the behavioural foundations of our cultural domestication. Even if helping a mother to deliver entailed nothing more than being present to obscure, distract or confuse a potential opportunistic predator, these behaviours could have been the basis for reciprocal relationships with others in the group. Moreover, the stress and relief associated with a potentially dangerous birth could have triggered emotions that foster motivations to shape behaviours. Those who sought and offered assistance could have passed on such traits to their own offspring, thus increasing the likelihood of this cooperative behaviour becoming an established social pattern in the species.

In the same way that domesticated dogs seek assistance, when faced with a problem, our earliest ancestors began to look to others for help. Childbirth as shared emotional experience in the evolution of social behaviour may be highly speculative, but for anyone who has witnessed a birth for the first time, the extent of the experience is unexpected, surprisingly emotional and often beyond reason and control, suggesting that it triggers behaviours that lie deep in the history of our species to help others.

Brain size and behaviour

Considering all the problems that giving birth to big brains seems to entail, we are still left with the question, ‘Why did our ancestors evolve much larger brains about 2 million years ago?’ One possibility that is consistent with the argument we began with is that a larger brain enabled animals to move around and keep track of where they have been. 22If you look at the animal kingdom, different patterns of feeding are related to different brain sizes. Primates who eat mostly fruits and nuts have larger brains than those primates who eat only leaves. Leaves are readily available in predictable locations and so require less foraging. Primates who live mostly on leaves have to consume much larger volumes of these low nutritional foods that then have to be broken down by enzymes in the stomach. This is why leaf-eating primates have much larger guts for fermenting the material. It also explains why they have to spend most of their day sitting around and simply eating and digesting.

In contrast, fruits and nuts are more nutritious but they are also sparse, more seasonal and more unpredictable. Coming down from the trees and learning to walk upright meant that foraging over greater distances by our ancestors would become the typical behavioural pattern. Bigger brains would have been necessary to find higher value nutritional foods that would have been necessary to maintain a bigger brain.

This is why fruit-eating primates have to travel much further to satisfy their dietary needs. They also have much smaller guts and proportionally larger brains. Their habitats are more extensive and require greater navigational skills so they are generally more active. Take spider monkeys and howler monkeys, two closely related species that live in the tropical rainforests of South America. The diet of the spider monkey is 90 per cent fruit and nuts, whereas howler monkeys live mostly on the rainforest’s canopy leaves. This difference in diet and the need to forage could explain why the spider monkey’s brain is proportionally twice the size of the howler monkey’s, with a corresponding greater level of problem-solving abilities.

But our early ancestors were not simply foraging for nuts and berries – they were beginning to process food and carcasses with rudimentary stone tools. Animals with large brains are better tool users and humans are experts who far exceed any of the tool-making skills of other animals. Even making the earliest simple stone tools required special skills that are uniquely human. The anatomy of the human hand and the brain mechanisms that coordinate dexterity enabled our ancestors to hold a flint in one hand and knap it into the right shape with the other – a skill so far not observed in non-human primates. 23Animals also tend to fashion tools from what is immediately available and abandon them soon after, whereas our ancestors hung on to their manufactured tools, carrying them around for future use. That requires a level of knowledge, expertise and intelligent planning to develop technology unprecedented in the animal kingdom – one notable exception being the sea otter that is said to carry a stone in its pouch that it uses for cracking seashells!

As unique as human tool use is, a significant increase in brain size occurred between 2 and 1.5 million years ago, and yet the oldest stone tools are between 3 and 2 million years old, predating the expansion of the hominid brain. 24There have been considerable developments in the sophistication of the tools following the expansion of the brain, but the invention of tool technology itself probably did not seem to depend on the significant increase in brain size.

Another class of explanation is required to explain the need to develop larger brains but one that can include changing patterns of both food exploration and hunting. Early humans not only foraged but they also increasingly hunted, which meant that they had to travel further and they had to collaborate. They had to understand each other and cooperate to satisfy mutual goals. They had to navigate a social environment as much as a physical one and this social environment would soon get crowded.

One big family tree

The fossil record shows that modern humans are the last survivors of a branch of the evolutionary tree or genus of the apes known as Homo that emerged during a period of time known as the Pleistocene that began some 2.5 million years ago. Recent discoveries in Kenya reveal that this was a crowded time, with multiple hominid species co-existing. 25Other members that would emerge later out of this branch include Homo hablis, Homo erectus, Homo heidelbergensis, Homo neanderthalensis and Homo floresiensis , nicknamed the ‘hobbit’ because of its small stature. All have become extinct, with floresiensis being the last to disappear, possibly as recently as 12–15,000 years ago. We are Homo sapiens (‘wise man’), who first appeared in Africa some 200,000 years ago. 26

In addition to evidence based on the fossil record, scientists have been able to reconstruct our human past by analysing the human DNA genome and looking for common sequences that reveal our relatedness. By using statistics, they can work out how long it took patterns to deviate to reconstruct our ancestry. One type of DNA, which is found outside the nucleus of cells known as mitochrondial DNA (mtDNA), has been particularly useful because it provides a way of tracing the history of our species and identifying the spread of humans across the globe. In a female, mtDNA is stored in her eggs and mutates at a different rate than cellular DNA. This difference in mutation rates enables researchers to establish various lineages back into the dark prehistory of our species. In 1987, researchers published results of mtDNA analysis and reported evidence that there was a common ancestor who must have lived in Africa around 200,000 years ago who was the ancestor for all modern humans. 27As this was based on the female mtDNA that was passed on to the thousands of her grandchildren, this hypothetical mother became known as ‘mitochondrial Eve’. Just recently, scientists have been able to extract DNA from Homo neanderthalensis to determine that we are related to this extinct subspecies, while also revealing a bit of a prehistoric scandal.

Homo sapiens and Homo neanderthalensis were known to be living close to each other in the same parts of Europe at around 40,000 years ago. Eventually, Homo sapiens became the last survivors. The more ancient Homo neanderthalensis, who first appeared on the scene 700,000 years ago, disappeared in Europe and it was assumed that they had been out-manoeuvred or wiped out by the Homo sapiens from Africa through competition for resources. However, it would now appear that there was some ‘Pleistocene hanky panky’ going on, as British-born palaeoanthropologist Ian Tattersall called it, referring to the genetic evidence of interbreeding. 28Analysis published in 2011 revealed that, on average, billions of people outside Africa have about 2.5 per cent of Neanderthal DNA in their genome. 29Of course, we cannot know whether this interbreeding was cooperative or forced, but it does paint a completely different picture of our species.