Is the Semi-Permanent "Gunpowder Empire" Historical Scenario Plausible? Perhaps Not...
Riffing off of yesterday's: : "'Gunpowder Empire': Should We Generalize Mark Elvin's High-Level Equilibrium Trap?"...From The Quarterly Journal of Economics via Brad DeLong:
A generation ago Michael Kremer wrote a superb paper: Michael Kremer (1993): "Population Growth and Technological Change: One Million B.C. to 1990", Quarterly Journal of Economics 108:3 (August), pp. 681-716 http://tinyurl.com/dl20160727a.
Kremer saw human populations as growing at an increasing rate over time. Population reached approximately 4 million by 10000 BC, 50 million by 1000 BC, and 170 million by the year 1. Population then reached 265 million by the year 1000, 425 million by 1500, and 720 million by 1750 before the subsequent explosion of the British Industrial Revolution and the subsequent spread of Modern Economic Growth.
Michael Kremer then developed this association between higher global population levels and faster population (and global real GDP, and global total factor productivity) growth into a "two heads are better than one" theory of long-run economic growth....MORE
POPULATION GROWTH AND TECHNOLOGICAL CHANGE: ONE MILLION B.C. TO 1990*
MICHAEL KREMER
The nonrivalry of technology, as modeled in the endogenous growth literature, implies that high population spurs technological change. This paper constructs and empirically tests a model of long-run world population growth combining this implication with the Malthusian assumption that technology limits population. The model predicts that over most of history, the growth rate of population will be proportional to its level. Empirical tests support this prediction and show that historically, among societies with no possibility for technological contact, those with larger initial populations have had faster technological change and population growth.
Models of endogenous technological change, such as Aghion and Howitt [1992] and Grossman and Helpman [1991], typically imply that high population spurs technological change. This impli- cation flows naturally from the nonrivalry of technology. As Arrow [1962] and Romer [1990] point out, the cost of inventing a new technology is independent of the number of people who use it. Thus, holding constant the share of resources devoted to research, an increase in population leads to an increase in technological change. However, despite its ubiquity in the theoretical literature on growth, this implication is typically dismissed as empirically undesirable.
This paper argues that the long-run history of population growth and technological change is consistent with the population implications of models of endogenous technological change. The first section of the paper constructs a highly stylized model in which each person's chance of being lucky or smart enough to invent something is independent of population, all else equal, so that the growth rate of technology is proportional to total population. The model also makes the Malthusian [1978] assumption that population is limited by the available technology, so that the growth rate of population is proportional to the growth rate of technology. Combining these assumptions implies that the growth rate of population is proportional to the level of population.
Figure I plots the growth rate of population against its level from prehistoric times to the present. The prediction that the population growth rate will be proportional to the level of population is broadly consistent with the data, at least until recently, when population growth rates have leveled off. The data, which are listed in Table I and discussed in Section IV, are drawn from McEvedy and Jones [1978], Deevey [1960], and the United Nations [various years]. While they are obviously subject to measurement error, there can be little doubt that the growth rate of population has increased over human history. Assuming that population has historically been limited by the level of technology, this much faster than exponential population growth is inconsistent with growth models which either assume constant exogenous technological change or generate it endogenously.
The model outlined in Section I is similar to that of Lee [1988], who combines the Malthusian and Boserupian interpretations of population history to generate accelerating growth of population. Lee adopts Boserup's [1965] argument that people are forced to adopt new technology when population grows too high to be supported by existing technology. However, this view is difficult to reconcile with the simultaneous rise in income and rates technological change over most of history, since it implies that increases in income should have led to reduced effort to invent new technologies. In contrast, this paper argues that even if each person's research productivity is independent of population, total research output will increase with population due to the nonrivalry of technology. As Kuznets [1960] and Simon [1977, 1981] argue, a higher population means more potential inventors. Lee's model and the simple model of Section I each make different functional form assumptions about the effect of population on technological change and of technology on population. While these restrictive assumptions make the models tractable, they limit their ability to match certain features of the data, such as the recent decline in population growth rates....MUCH MORE (37 page PDF)
