Adam Tooze​ wrote recently about the challenge posed by economic statistics both to historical actors and to historians. The upshot is that all national economic statistics must be taken with a pinch of salt. This concern has prompted me to focus on human stature instead of per capita income and output per worker as the carrier of information on global polarization. What I have discovered has astonished me. The picture that emerges suggests that latitude was not in fact all that important until the passage to modernity. Indeed, the empirical evidence reveals that the world got polarized along latitude only in the twentieth century. It suggests that a satisfactory history of global polarization has yet to be written; one that ties the polarization of global living standards to the Second Industrial Revolution.

The basic outline of human statures over the past three hundred years is that until about the mid-nineteenth century the classic premodern pattern held—everywhere we had medium-term cycles characteristic of the Malthusian Trap and a significant settler colonial premium in stature. In 1860-1890, the settler colonial premium vanishes, but global polarization was still modest. It is not until 1920-1960 that we hit the hockey stick in earnest. In the century 1860-1960, Western heights grew 10cm on average; 7cm in 1920-1960 alone. Elsewhere heights grew much more modestly. By 1960, global statures stabilized in the modern pattern—highly polarized along latitude with the Dutch leading the way. Everyday living standards were revolutionized by the Second Industrial Revolution because it was broad-based enough to repeal the Malthusian Law. That’s why the settler premium vanished and we hit the hockey stick. Any explanation of global polarization must take latitude as the point of departure because thermal burdens dictate the work intensity that can be sustained on the factory floor and therefore the cross-section of output per worker.

With this interpretation in mind (premodern 1700-1890, hockey stick 1920-1960, modern regime 1960-) the following estimates make for very interesting reading. Turns out, latitude was not the strongest correlate of stature in premodern 1880; it was cattlehead per capita. (As it presumably had been since the Secondary Products Revolution.) To be sure, latitude was definitely priced in as well. But latitude explained less than 10 percent of the variation. (The percentage of the variation in Y explained by X is just the square of the gradient once we standardize both X and Y to have mean 0 and variance 1.)  Meanwhile, cattle per head explained 37 percent of the cross-sectional variation in 1880. This is evidently the premodern pattern. Given the extraordinary cost of bulk transport, the governing variable for stature was the local availability of protein (meat and secondary). It is astonishing that this premodern pattern persists until as late as 1880. The exit from the Malthusian Trap was indeed very, very slow.

By 1920, the relative positions of latitude and cattlehead per capita had reversed. The latter fell into insignificance. But latitude explained no more than 18 percent of the cross-sectional variation so that everyday living standards were still only modestly polarized. It is only in 1960 (and thereafter) that the coefficient of latitude becomes 0.68, meaning that it singlehandedly explained 46 percent of the cross-sectional variation in stature. This corresponds to the considerably heightened polarization in everyday living standards in the modern era (1960-). Cattlehead meanwhile continues to be priced in (even after controlling for latitude) but explains only a modest 5 percent of the variation. See the estimates reported in Table 1-3 below and Figure 3 above.

Before the turn of the century, latitude was priced into the cross-section of stature but not after controlling for cattlehead per capita. Astonishingly, even per capita income is not a significant correlate of stature (in 1920 and 1960—we don’t have sufficient observations to test this in 1880) once we control for latitude or disease burdens (infant mortality). The evidence can be read off Table 1-3.

The empirical case for the Heliocentric model becomes even stronger once we observe that per capita income and disease burdens (and cattlehead until 1920) are themselves functions of latitude. See Table 4.

What is especially striking is that gain in per capita income is a poor predictor of gain in stature. Change in per capita income in 1920-1960 does not explain gain in stature in the same period (although admittedly, the sample is small). What explains the cross-section of the gain in stature is again latitude. See Table 5. Also compare the bottom-right graphs in Figure 2, Figure 4, and Figure 5.

So the question is not whether but why global living standards are polarized along latitude. Moreover, the weight of the empirical evidence suggests a very late date for polarization in living standards. Before the onset of the global condition living standards were not radically different across the world. As late as 1920, the gradients were modest. Polarization in global stature really and truly obtains only during the mid-century passage, 1920-1960. This is consistent with the modern understanding of global living standards we find in the work of David Edgerton and Adam Tooze. Fascinating that one can read it off the cross-section of stature so clearly.