Larger Populations Triggered Stone Age Learning

Anthropologists have come up with a theory about what kicked off a series of "creative explosions" in human ingenuity during the Stone Age — from about 90,000 to 45,000 years ago — and it doesn't involve some sudden improvement in brain power.

Instead, the flowering of intelligence that brought sophisticated tools, better weapons and art came about because of population density: More people started living in bigger communities.

That's the conclusion, described in the current issue of the journal Science, of a group of scientists at University College London. It's not the first time anthropologists have suggested that intellectual power arose from numbers, not biology. But the British scientists have created a mathematical model that, along with archaeological evidence, shows how inventions might have proliferated faster and more permanently once large communities of hunter-gatherers formed.

A Tipping Point For Learning

"Anything that we teach is going to be susceptible to loss, or to decay," says Mark Thomas, an evolutionary geneticist at UCL, unless there are plenty of people to adopt and carry on a new invention. "So if there are more people in the population, then more complex skills can be maintained in that population without that decay."

Essentially, a group needs to reach a certain threshold population before there are enough good learners and teachers to guarantee that a new skill will be retained.

Thomas says his mathematical model suggests that you need about 200 people living in an area of about 35 square miles to get that kind of learning community. But he says you don't need the math to get the idea.

"If you take random people from around the world, 20 people, and ask somebody to play the guitar, you might get one with a little strum," he says. "But if you take 100,000 people and look for the person who plays the best, on average they're going to be considerably better than somebody from a room of 20 people, right?"

Mixing And Sharing

There's something else that has to have happened for inventions to spread, though — lots of different communities. Human groups tended to trade ideas as well as goods when they ran into each other — if they didn't kill each other first, says Rick Potts, head of the Human Origins program at the National Museum of Natural History in Washington, D.C.

"You can increase population size, but ... you have to subdivide it into groups that can hold on to different innovations, in a sense be different experiments."

So having a minimum number of groups, and migration that brought them together, is another essential part of the hypothesis.

The scientists say their scenario doesn't rule out the possibility that some biological change in the human brain kick-started modern thinking and technology — only that there are other ways it could have happened, without any need for a "magic spark," as Thomas put it, to get the brain rolling.

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