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What lit the fuse of culture?

A new study has population density sparking 'modern' societies

by Rowan Hooper

In this month’s column, we solve the mystery of the emergence of modern human culture. As a bonus, there’s a bit of good news for Tokyoites — and for those of us who may worry that success is solely down to brainpower.

After I moved to Japan, I gradually adjusted the cultural peculiarities I’d picked up from living in Britain, and made myself more Japanese. Like many foreigners in Japan, I learned to ask questions obliquely; I became far more polite than I had been at home; and I changed my eating habits.

I couldn’t change my genes, of course, but I could change my behavior. So, to some extent, I could adapt to the different cultural environment I found myself in. It’s something that marks humans out from other animals.

Some animals have culture, but ours is far richer. Our culture and our ability to spread it to others, and to learn from others to whom we are not related, is one of the keys to human success.

However, we took a long time to get going.

Modern humans have been around for at least 160,000 to 200,000 years. Skeletons from that period show that anatomically we are very similar now to then. Over all those millennia, the brains of humans didn’t change too much. However, until around 90,000 years ago there is no archaeological evidence of any technology beyond basic stone tools. What took our ancestors so long?

A new study in the journal Science now suggests that it was increasing population density, rather than a mysterious boost in human brainpower, that catalyzed the emergence of modern human behavior.

Since Tokyo is the most densely populated metropolitan area in the world, with around 4,049 people per sq. km, Tokyoites can take heart that, despite the crush, they are in the best place in the world for the transmission of new ideas and skills.

Adam Powell and colleagues at the Centre for the Evolution of Cultural Diversity, at University College London, ran computer simulations of social learning. They first showed that high- and low-skilled groups of people could coexist over long periods of time, and that the degree of skill they maintained depended on local population density or the degree of migration between them.

Then the team used genetic estimates of population sizes in the past, and showed that the density of humans was similar in sub-Saharan Africa, Europe and the Middle East when modern behavior first appeared in each of those regions.

In other words, population size may be the factor that ignites a boom in human culture. It explains why advanced technology and behavior takes off in Europe and western Asia about 45,000 years ago, when human numbers in those parts of the world reached a critical size there — and why it doesn’t appear in eastern and southern Asia and Australia until much later, despite there being some humans present.

“Scientists have offered many suggestions as to why these cultural explosions occurred where and when they did — including new mutations leading to better brains; advances in language; and expansions into new environments that required new technologies to survive,” says archaeologist Stephen Shennan from UCL.

“The problem is that none of these explanations can fully account for the appearance of modern human behavior at different times in different places, or its temporary disappearance in sub-Saharan Africa,” he cautions.

It used to irritate me when I was a child that humans still hadn’t developed the technology to travel to other planets. This study does bring back a little of that irritation.

We took tens of thousands of years to build up population sizes big enough to usefully exchange information — but then we still scrabbled around in the dirt for tens of thousands of years more.

Gradually, though, we started doing things that other animals don’t. We decorated our bodies with beads and tattoos; we made musical instruments, bone artefacts, stone blades and more sophisticated hunting and trapping technology, like bows, boomerangs and nets.

However, just when we really started to work things out, the Dark Ages in Europe came along and held us back. When the western Roman Empire fell in the fourth and fifth centuries A.D., a culture of learning fell with it, and it was at least 600 years until it was recovered.

The loss of the 600 years is annoying. Just imagine what we’ll be able to do in 600 years from now. (Actually, that’s assuming we haven’t cooked ourselves to death through global warming. Perhaps I wouldn’t even be here if there hadn’t been the Dark Ages to delay the Industrial Revolution of the late 18th and early 19th centuries, and the consequent massive, man-made changes in climate.)

As far as we can tell, humans’ brains were the same in Ancient Greece as they are now. Hell, they were the same in prehistoric Africa, some 150,000 years ago. The new work suggests that there was no sudden change, divine or otherwise, that made us what we are now.

“When we think of how we came to be the sophisticated creatures we are, we often imagine some sudden critical change, a bit like when the black monolith appears in the film ’2001: A Space Odyssey,’ ” says another team member, geneticist Mark Thomas.

“In reality, there is no evidence of a big change in our biological makeup when we started behaving in an intelligent way. Ironically, our finding that successful innovation depends less on how smart you are than how connected you are, seems as relevant today as it was 90,000 years ago.”

The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains Your Journey Through Life).”