What led to the birth of human civilization? How did a naked ape manage to invent complex cultural forms such as language and art? One possibility is that something happened inside the mind, that a cortical switch was flipped and homo sapiens was suddenly able to paint on cave walls. But that doesn’t seem to be the case, as UCL anthropologist Ruth Mace explains in a recent Science article:
Traits such as the creation of abstract art, improvements in stone and other tools, long-distance “trading,” and the manufacture of musical instruments mark the emergence of modern humans who behaved much as we do (see the figure). These material expressions of the modern condition emerged much later than did anatomically modern humans. Some aspects of behavioral modernity first appeared in southern Africa, possibly as early as 90,000 years ago, only to disappear again and reappear in Eurasia ~45,000 years ago. The timing of these events makes a biological change in cognitive capacity a somewhat unlikely explanation.
What, then, led to the birth of “modern human behavior”? A new paper by Adam Powell, et. al. argues that the crucial shift was increasing population density. The main evidence for this effect comes from genetic studies of the late Pleistocene, which demonstrate that “densities in early Upper Paleolithic Europe were similar to those in sub-Saharan Africa when modern behavior first appeared.”
The larger implication is that the birth of human culture was triggered by a new kind of connectedness. For the first time, humans lived in dense clusters, and occasionally interacted with other clusters, which allowed their fragile innovations to persist and propagate. The end result was a positive feedback loop of new ideas.
While it’s very nice to have some statistical evidence for this idea (even if I can’t pretend to understand the “Bayesian coalescent inference” method used by the scientists to calculate the population densities in the late Pleistocene), it’s worth pointing out that the density explanation isn’t particularly new. In The Economy of Cities, Jane Jacobs forcefully argued against the “dogma of agricultural primacy,” which assumed that farmers and agricultural innovations made civilization possible. Jacobs argued that the dogma was exactly backwards, and that it was the density of urbanesque clusters which generated the innovations that made farming possible. As Jacobs writes: “It was not agriculture then, for all its importance, that was the salient invention…Rather it was the fact of sustained, interdependent, creative city economies that made possible many new kinds of work.” After all, you can’t learn how to grow food until you’ve got a system for transmitting knowledge, which is why population density is so essential.