In a paper released today in Science Advances, 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.”
The researchers drew their conclusions from a close analysis of archaeological survey data on about 4,000 pre-Hispanic settlements in the Basin of Mexico that date from ancient times through the end of the Aztec era in the 16th century. Among other things, the surveys documented the size, shape, and general measures of all sorts of buildings from these settlements. These included the likes of civic monuments as well as individual homes.
Such details gave Ortman and collaborators an impressive window into urban life from much earlier times. They first looked specifically at the size and volume of monuments in these settlements, with the idea that such buildings reflect productivity of a city—a sort of ancient proxy to modern GDP. If social interactions truly enhanced urban life in a universal way, they would expect to see monument size increase with city size, just as GDP does in urban areas today.
Indeed, they found just that. The chart below shows that monument size (the solid line) grew at a “super-linear scale” in big cities—in other words, faster than the population growth rate (the dotted line). Larger groups of urban laborers built bigger monuments than smaller groups, and built them faster. The researchers attribute the boost in productivity to the collective power of social networks in these cities, given the limited technological advances identified over this period.