Welcome, Child Seven Billion
History shows we have nothing to fear from growing population.


Robert Zubrin

So the question is: What causes the advance of technology? Well, clearly, technology does not come from the land, it comes from people. It is the product of human work. The most general way to measure human work is in terms of person-years. So let’s graph the growth in technology (using GDP per capita as a proxy measure) against human person-years expended, from the year 1 AD to the present. The results are shown in Figs. 4 and 5. (I’ve used two graphs to show this to avoid the necessity of using logarithmic scales, which are harder to read.)

Fig. 4: Growth of technology with respect to person-years, 1 AD to 1875

The growth of human technology worldwide from the time of the Roman and Han Empires to the late nineteenth century basically breaks down into three periods: that before 1500, that from 1500 to 1800, and that after 1800.

From 1 AD to 1500, technology does grow, but only at a very slow rate of 17.5 percent over 460 billion person-years, or an average of 0.035 percent per billion person-years. Between 1500 and 1800, the pace picks up substantially, with GDP per capita increasing by 58 percent in 200 billion person-years, or 0.23 percent per billion person-years, a more than sixfold increase over the preceding period. Then, around 1800, technology takes off, with GDP per capita growing 116 percent over the next 90 billion person-years. As shown in Fig. 5, this growth continues, showing a 4,700 percent increase over the entire 500 billion person-year span from 1800 to 2010, for an average growth rate of 0.8 percent per billion person-years.

Fig. 5: Growth of Technology with respect to person-years, 1400–2010

These results make perfect sense. Before 1500, there really wasn’t a world economy in any substantial sense, because long-distance trade and communication was so limited. Rather than a world economy, what existed was a number of disparate civilizations including European Christendom, the Islamic world, India, China, Mexico, and Peru, each with their own economy. Important innovations made in one civilization could take centuries or even millennia to propagate to the others. Thus, for example, it took hundreds of years for such important Chinese inventions as paper, printing, and gunpowder to reach Europe, and thousands of years for European domesticated horses, wheeled vehicles, and numerous other technologies to reach the Americas. Thus, the relevant inventive population size driving the advance of each civilization was not the whole world population, as small as it was, but the much smaller population of the civilization itself.