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Book Summary: The Book of Humans: A Brief History of Culture, Sex, War and the Evolution of Us

Author: Adam Rutherford

Substory: Teach a Village to Fish

We’ve seen that there is little physical difference between a woman or man 100,000 years ago, and you or I today. We can see almost certainly that language is older than the onset of the full human package. Our brains are not significantly different from when we were just dabbling with art, and indeed they don’t seem fundamentally different from those artists who were not us, but our cousins the Neanderthals. The symptoms of modernity have been with us for tens of thousands of years longer than its arrival. Evidence is found scattered in Europe and Indonesia by 40,000 years ago. There are examples of modernity in Africa and Australia within a few millennia after it’s seen in Europe as well. These make a genetic basis for the change unlikely, as they are spread over the world with no interaction, no gene flow, between these peoples. If we are to assume that all the humans that spread around the world had emerged from Africa, and were genetically similar, then it’s unlikely that they independently will have enjoyed the same DNA mutations that triggered the arrival of a complex mind. If the Palaeolithic people of the world were biologically similar, the question is this: why did it take so long to become modern when we were physically ready for thousands of years?

There are many pieces of this puzzle that remain elusive. These are areas of research that are beginning to blossom, such as theory of mind, and the nature of consciousness. They are questions that have languished in fascinating philosophical realms for decades and centuries, and are beginning to be examined with the more precise scientific tools of the twenty-first century. We inch towards a better understanding of those areas as they become entwined with neuroscience.

There’s one idea that I think is crucial, that has been emerging in the last few years, but is not yet discussed widely, though I hope it will be soon. It is that population size and structure changed, and with those changes, modernity followed. The full package came about because of how we organised our society.

The first clue to this theory is that populations seem to grow larger at the time of the onset of modernity, in multiple locations. We see it in Africa 40,000 years ago, and at a separate time in Australia, more like 20,000 years ago. These expansions may be in line with the local environment, simply that as the climate changed, life became easier. They might also be a manifestation of our huge migrations. No other creature has moved permanently in such a short period of time – within 20,000 years of leaving Africa, we had settled in Australia.

We also see the opposite effect: a loss of cultural sophistication in societies whose populations do not grow, migrate or are cut off from a bigger populace. For example, Tasmania became an island around 10,000 years ago, as the last Ice Age thawed and the seas rose, and was separated from mainland Australia by what Europeans named the Bass Straits. The indigenous people of Tasmania managed to maintain a tool kit of only twenty-four pieces in that isolation, and lost the skills to make dozens of others over thousands of years in the Neolithic. Indigenous Australians on the mainland developed more than 120 new tools during the same period, including multi-toothed bone harpoons.

In the Tasmanian archaeological record, we see the gradual disappearance of fine bone tools, the loss of the ability to make cold-weather clothing, and perhaps most significantly, the degradation of fishing technology. Hooks and spears for catching cartilaginous fish vanish from archaeology, as does evidence of fish bones (although they did continue to forage and eat crustaceans and sessile molluscs). When Europeans arrived in the seventeenth century, the indigenous people expressed both surprise and disgust at the colonisers’ skill at catching and eating large fish, yet 5,000 years earlier it was a key and thriving part of their diet and culture.

Scientists who are interested in the full package have developed models to try to understand how the cultural transmission of skills is affected by the size and structure of a population.1 In this way, they can test how and why we see the hallmarks of modern behaviour come and go, and eventually stay in the archaeological record. These are effectively equations that model how an idea or skill is passed around in a community. They plug in hypothetical numbers for the size and density of a population, and a skill level for an imagined expert task – maybe knapping an arrowhead, or tooting a flute – and then they run simulations that work out how that skill level can be transferred between people. Mathematical models of this sort are pretty technical, but what they are effectively doing is saying: ‘Here are people with a very particular set of skills, which can be taught to others. How does the size of a population affect the efficiency of teaching?’

The answer appears to be ‘enormously’. Larger populations enable the transfer of complex cultural skills with far greater efficiency than smaller ones. The maintenance of skill levels is heavily dependent on population size (which is also affected by migration). According to the models, small populations, especially isolated ones, will lose skills through an inefficient transmission. When populations grow, they accumulate culture more readily. Only we do this. Though there is a smattering of other examples of cultural transmission in other animals, we do it all the time.

I don’t think that demographics is necessarily an obvious link to how we became who we are, which might be why it has been relatively neglected. But when we look at what humans are, it makes perfect sense. We are social, meaning that we depend upon the interactions with others for our own well-being. We are cultural transmitters, meaning that we pass on a wealth of knowledge that is not encoded in our DNA. We do this horizontally, not just vertically, meaning that we teach to people who are not our children, but are our peers, and may not even be genetically close kin. And we are highly skilled and creative, but that expertise is not distributed evenly throughout our populace – some people have skills that others don’t, and when we need to find out how to do something, we ask an expert.