West does not mention another scaling law that works in the opposite direction. That is the law of genetic drift, mentioned earlier as a crucial factor in the evolution of small populations. If a small population is inbreeding, the rate of drift of the average measure of any human capability scales with the inverse square root of the population. Big fluctuations of the average happen in isolated villages far more often than in cities.

On the average, people in villages are not more capable than people in cities. But if ten million people are divided into a thousand genetically isolated villages, there is a good chance that one lucky village will have a population with outstandingly high average capability, and there is a good chance that an inbreeding population with high average capability produces an occasional bunch of geniuses in a short time.

A substantial fraction of the population of Europe and the Middle East in the time between 1000 BC and 1800 AD lived in genetically isolated villages, so that genetic drift may have been the most important factor making intellectual revolutions possible. Places where intellectual revolutions happened include, among many others, Jerusalem around 800 BC (the invention of monotheistic religion), Athens around 500 BC (the invention of drama and philosophy and the beginnings of science), Venice around 1300 AD (the invention of modern commerce), Florence around 1600 (the invention of modern science), and Manchester around 1750 (the invention of modern industry).

These places were all villages, with populations of a few tens of thousands, divided into tribes and social classes with even smaller populations. In each case, a small starburst of geniuses emerged from a small inbred population within a few centuries, and changed our ways of thinking irreversibly. These eruptions have many historical causes. Cultural and political accidents may provide unusual opportunities for young geniuses to exploit.

But the appearance of a starburst must be to some extent a consequence of genetic drift. The examples that I mentioned all belong to Western cultures. No doubt similar starbursts of genius occurred in other cultures, but I am ignorant of the details of their history.

West’s neglect of villages as agents of change raises an important question. How likely is it that significant numbers of humans will choose to remain in genetically isolated communities in centuries to come? We cannot confidently answer this question. The answer depends on unpredictable patterns of economic development, on international politics, and on even more unpredictable human desires.

But we can foresee two possible technological developments that would result in permanent genetic isolation of human communities. One possibility is that groups of parents will be able to give birth to genetically modified children, hoping to give them advantages in the game of life. The children might be healthier or longer-lived or more intellectually gifted than other children, and they might no longer interbreed with natural-born children.

The other possibility is that groups of people will emigrate from planet Earth and build societies far away in the depths of space.