But for a true sense of the rapidity of events, look no further than the Y chromosome. The most comprehensive analysis of the Y yet shows that within 150 years, an evolutionary blink of an eye, the first migrants to make it into Eurasia split into three distinct groups that can still be identified today.

Men inherit their Y chromosome from their fathers. Like all other chromosomes, the Y mutates over time so the more distant the relationship between two men, the more genetically distinct their Y chromosomes. In 2000, biologists used this fact to construct a family tree of all men, which shows how human populations around the world are related.