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Human evolution: why we’re more than great apes

Palaeoanthropologists have used the anatomical signs of bipedalism to identify our earli­est ancestors, demonstrating our shared genetic heritage with great apes. However, despite this shared history, human evolution set out on a trajectory that has led to significant distinctions from other primates.

In this shortened excerpt from Human Evolution: Our Brains and Our Behavior, evolutionary psychologist Robin Dunbar explains the link between culture and the human brain—and how that connection distinguishes us from other primates.

We share with the other great apes a long history, a largely common genetic heritage, a similar physiology, advanced cognitive abilities that permit cultural learning and exchange, and a gathering and hunting way of life. And yet we are not just great apes. There are some radical differences. The least interesting of these, although the ones that almost everyone has focused on, are the anatomical differences, and in particular our upright bipedal stance. In fact, most of these traits are just bits of early remodeling to allow a mode of travel that became a route out of certain extinction as the Miocene climate deteriorated and the tropical forests retreated. Much of the rest of the debate has hinged around instrumental behaviors like tool-making and tool use. But in reality these are cognitively relatively small beer – even crows make and use tools, with a brain that is a fraction the size of a chimpanzee’s. The substantive difference lies in our cognition, and what we can do inside our minds. It is this that has given us Culture with a capital ‘C’, culture that produces literature and art.

Over the last two decades, a great deal of research has been done – and even more ink spilled in learned journals – arguing the case for culture in animals, and especially in the great apes. The field has even coined a name for itself: panthropology, the anthropology of Pan, the chimpanzee. It should come as no surprise that behaviors and cognitive abilities that characterize modern humans are also found in some form in our nearest relatives. That is in the nature of evolutionary processes: traits seldom arise completely de novo out of the blue. In most cases, they arise as adaptations of existing traits, which become exaggerated or radically modified under the influence of novel selection pressures. We shall examine some of these later. For the moment, the important point to establish is that, yes, humans and chimpanzees share the ability to transmit behavioral patterns socially by cultural learning, and, yes, we can reasonably argue for culture in chimpanzees and other great apes, but the reality is that what apes do with their cultural abilities simply pales into insignificance by comparison with what humans do. This is not to belittle what monkeys and apes do, but rather to identify the substantive issue that seems to get overlooked in all the brouhaha and excitement: humans somehow raised the whole game by a great deal more than just a couple of notches. How did they do this, and why?

There are probably two key aspects of culture that stand out as being uniquely human. One is religion and the other is story-telling. There is no other living species, whether ape or crow, that do either of these. They are entirely and genuinely unique to humans. We know they must be unique to humans because both require language for their performance and transmission, and only humans have language of sufficient quality to allow that. What is important about both is that they require us to live in a virtual world, the virtual world of our minds. In both cases, we have to be able to imagine that another world exists that is different to, and separate from, the world we experience on an everyday basis. We have to be able to detach ourselves from the physical world, and mentally step back from it. Only when we can do this are we able to wonder whether the world has to be the way it is and why, or imagine other parallel worlds that might exist, whether these are the fictional worlds of story-telling or para-fictional spirit worlds. These peculiar forms of cognitive activity are not trivial evolutionary by-products, but capacities that play – and have played – a fundamental role in human evolution.

What underpins all this cultural activity is, of course, our big brains, and this might ultimately be said to be what distinguishes us from the other great apes. Seen on the grand scale of the last six million years, hominin brain size has been on a steady upswing in which brains trebled in size from their ape-like beginnings among the australopithecines to the brains of modern humans. This seems to suggest that there has been continuous upwards pressure for bigger and bigger brains over time. However, this does not necessarily mean that the selection pressure for larger brains has been increasing steadily over time. In fact, the continuous increase over geological time is an illusion, created by pooling specimens from the different species together. Separating the species out gives a pattern that is more suggestive of punctuated equilibria: each new species generates something more akin to a rapid increase or phase shift in brain size when it first appears, and then brain size stabilizes across time.

To a large extent, the trajectory that defines our pathway over these 6–8 million years reflects the dramatic changes in brain size and organization that mark out the sequence of events that makes up this story – the speciations, the migrations, the extinctions, and the cultural novelties that litter the timeline of hominin evolution. Associated with these changes in brain size are a number of other core traits, some of which we can infer from the archaeological record and some of which we know reliably only from modern humans. Some are anatomical, some behavioral or cognitive, but all have to be fitted into a single seamless sequence against both the changes in brain size (and hence group size) and the constraints of time, as well as the archaeological record. It is this triangulation between the different sources of information that makes our task possible, since it allows us much less room for speculative maneuver than has hitherto been the case. We cannot assemble the pieces of the jigsaw in any random order and simply make up some plausible story for the particular pattern we happen to favor. Instead, our approach will allow us to provide principled reasons for assembling the pieces in a particular order – or at least arriving at a limited number of alternative possible ways of doing so.

Read entire article at OUPblog