Settlement scaling and increasing returns in an ancient society

The more scientists study urban development, the more they realize that cities are like nothing else in nature.1 The social interactions that occur in a dense setting have a multiplier effect: they create more wealth, greater ideas, and larger buildings, though they can also spread more disease. At a certain point, in ways good and bad, city life adds up to far more than the sum of individual city lives.

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In a paper released today in Science Advances,2 Ortman and collaborators (including Bettencourt) report what they call "striking and exciting" new evidence supporting just that hunch. The researchers report that productivity was greater in large ancient cities just as it is in dense urban areas today—though the nature of that production was monument and building size, rather than modern economic measures like GDP.

The work supports the basic idea of cities as great "social reactors." In dense places, communal assets set in close proximity (such as food gathering or transport networks) free up people to direct energy in more beneficial directions (such as labor coordination or knowledge specialization). Highly dispersed places, where social connections are farther apart, don't reap the same productivity gains.

"One thing that really strikes me is that this research suggests that humans—human groups—do generally benefit from coordinating their behavior at larger scales," says Ortman. "In a sense, there's a reason why the human population is rapidly urbanizing today. This work suggests that overall there really are intrinsic advantages to larger scales of social organization."

  • 1. Scientific Proof That Cities Are Like Nothing Else in Nature

    “People have thought about cities just about every possible way since the Greeks,” says Luis Bettencourt, a physicist with the Santa Fe Institute, the scientific research and education center. “It’s an incredibly rich topic, and I think the curious thing is that we’ve tried to throw every analogy at it. But there’s a sense in which most of them fail somewhere. And to me, what that always meant was that we needed to discover better what cities really are.” 

    You may by now be familiar with some of the mind-bending findings that have come out of the Santa Fe Institute, from Bettencourt and his colleague Geoffrey West and others. Over the last several years, they’ve been processing data that never existed before on all kinds of quantifiable characteristics of cities: the length of road networks, the average income of inhabitants, the number of patents per capita. And they’ve found that all of these characteristics scale with city size: As population grows, so do all of these other factors, in remarkably predictable ways across the globe and throughout time.

    ....

    The idea that cities are governed by some universal rules of math may make it sound like the urban planner has little control. But, in fact, Bettencourt sees the planner’s job to try to steer cities toward that optimal point (G*) on the above graph. Beyond that point, the number of social interactions in a city can still grow, but the cost of them rises faster than the benefit.

    Ideally, as cities grow, all of this means that they should become even more productive, even more powerful. And in this way, at least, they are like one thing in nature. As stars compress matter, they burn brighter and faster the bigger they are. But stars can eventually run out of energy. They’re not open-ended. And they’re isolated systems, where cities rely on food and other resources from beyond their borders.

  • 2. Settlement scaling and increasing returns in an ancient society

    Scott G. Ortman, Andrew H. F. Cabaniss, Jennie O. Sturm, Luís M. A. Bettencourt
    Science Advances 01 Feb 2015:
    Vol. 1 no. 1 e1400066, DOI: 10.1126/sciadv.1400066

    A key property of modern cities is increasing returns to scale—the finding that many socioeconomic outputs increase more rapidly than their population size. Recent theoretical work proposes that this phenomenon is the result of general network effects typical of human social networks embedded in space and, thus, is not necessarily limited to modern settlements. We examine the extent to which increasing returns are apparent in archaeological settlement data from the pre-Hispanic Basin of Mexico. We review previous work on the quantitative relationship between population size and average settled area in this society and then present a general analysis of their patterns of monument construction and house sizes. Estimated scaling parameter values and residual statistics support the hypothesis that increasing returns to scale characterized various forms of socioeconomic production available in the archaeological record and are found to be consistent with key expectations from settlement scaling theory. As a consequence, these results provide evidence that the essential processes that lead to increasing returns in contemporary cities may have characterized human settlements throughout history, and demonstrate that increasing returns do not require modern forms of political or economic organization.