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Reconstructions

Scientists can't decide if shoulders of giants were broader or just better organized

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The people who lived in Tasmania 8,000 years ago were pretty sophisticated, technologically speaking. They made bone tools, boomerangs, nets for catching a variety of prey and warm clothing to protect themselves from blustery weather. But when Europeans came upon that island, off Australia’s southern coast, just a few centuries ago, they found some of the most primitive hunter-gatherers in the world — subsisting without seaworthy vessels, sewn clothing or bone tools of any kind.

What happened to the Tasmanians over the intervening millennia is a favorite mystery of anthropologists, because it looks like human history in reverse: Over the course of a few thousand generations, Homo sapiens developed tools, skills and social structures that have enabled the species to go from scratching out a living in isolated African populations to dominating the global ecosystem. How on Earth did we do it?

It could be that a sudden and dramatic advancement in human capacity for thinking and communicating, such as the development of language, spurred the rapid expansion of the species out of Africa and around the world. Or it may be that Homo sapiens is not so special in its mental abilities vis-à-vis extinct relatives like the Neandertals, but instead that social organization and living in large, stable groups gave humans an advantage in developing and preserving innovations.

One way to try to resolve that debate is with a little math. Anthropologist Joseph Henrich of the University of British Columbia was thinking about the Tasmanian question in 2004 when he wrote an equation showing how the isolation of the island after the last Ice Age, which ended about 10,000 years ago, might have led to a gradual loss of technological prowess. Because sea level was lower during the Ice Age (a lot of water that’s now in the oceans was locked up in polar glaciers instead), what is now the island of Tasmania was connected to the Australian mainland. When the seas rose and the Tasmanians were left in their own little world, maybe they didn’t even have a sufficient talent pool to preserve the technologies they already had.

Since then, Henrich’s equation, published in American Antiquity, has been applied to the much bigger question of how H. sapiens came to dominate the globe. At its core are two numbers meant to get at how culture gets transmitted. The first number, symbolized by alpha, is meant to describe the ease of accurately transmitting a skill from one generation to the next. Assuming that a young person would seek out the most skilled teacher possible for any given skill, that number is usually negative because, on average, a neophyte is never going to match a master of the craft. But occasionally, there will come a prodigy who can replicate a technique with even better results than the teacher.

The second number, beta, is meant to encompass the room for experimentation and serendipity in a given skill. If beta is big, there’s a greater likelihood that doing it your own way will result in a better outcome than the previous generation’s efforts.

Obviously, the more people you have in a society, the greater the chances that one of them will have a combination of skill and inspiration to surpass those who came before. As a population shrinks, it will tend to lose technologies that are more complex (high alpha) and that leave less latitude for variation in technique (low beta). That seems to be what happened in Tasmania.

Henrich’s model may also explain why humans were able to outcompete Neandertals in Europe and any number of competitors in Stone Age Asia. Larger groups and social structures may have been all it took to put Homo sapiens on the road to world domination, he suggests.

But now, a pair of researchers from the University of Tokyo has used Henrich’s math to come to the exact opposite conclusion. Ingenuity, not social structure, has been the secret to humankind’s success over the last 50 or 100 millennia, they argue in a paper to appear in the August issue of Theoretical Population Biology.

Yutaka Kobayashi and Kenichi Aoki make a few embellishments to Henrich’s original equation. They tweak it so people aren’t lumped into arbitrary generations, but learn continuously throughout life. And the researchers combine alpha and beta into an “innovativeness” measure. With those modifications, a fivefold increase in innovativeness leads to rapid advances in cultural complexity, even in a population of just a few hundred people. In their analysis, boosting innovativeness turns out to be a much more potent source of technological advancement than population size.

This debate over human cultural development may seem esoteric, with all its mathematical abstractions meant to represent real human behavior. What, after all, is a fivefold increase in innovativeness? But behind the math is a fundamental dispute about what it means to be human: whether it’s what’s in our heads and how we use it to manipulate the world around us, or it’s how we organize ourselves into groups that pass knowledge from one generation to the next.

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