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.25 Other 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.27 As 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.28 Analysis published in 2011 revealed that, on average, billions of people outside Africa have about 2.5 per cent of Neanderthal DNA in their genome.29 Of course, we cannot know whether this interbreeding was cooperative or forced, but it does paint a completely different picture of our species.
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.30 Domestication 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.31 Many 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