Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past

by David Reich

The time around five thousand years ago coincides with the period in Eurasia that the archaeologist Andrew Sherratt called the “Secondary Products Revolution,” in which people began to find many uses for domesticated animals beyond meat production, including employing them to pull carts and plows and to produce dairy products and clothing such as wool.19 This was also around the time of the onset of the Bronze Age, a period of greatly increased human mobility and wealth accumulation, facilitated by the domestication of the horse, the invention of the wheel and wheeled vehicles, and the accumulation of rare metals like copper and tin, which are the ingredients of bronze and had to be imported from hundreds or even thousands of kilometers away. The Y-chromosome patterns reveal that this was also a time of greatly increased inequality, a genetic reflection of the unprecedented concentration of power in tiny fractions of the population that began to be possible during this time due to the new economy. Powerful males in this period left an extraordinary impact on the populations that followed them—more than in any previous period—with some bequeathing DNA to more descendants today than Genghis Khan.