While I was writing The Cancer Chronicles, I came to a point, early on, where I wondered how many people had ever been alive in the world. The best answer I could find came from a study by an organization called the Population Reference Bureau: 108 billion.

It is still common to hear that more people are alive today than have ever lived. Or an even more extreme claim: that 75 percent of everyone who ever walked the earth is living today. But that is not even close to being correct.

Carl Haub describes the assumptions that went into his calculations. Modern homo sapiens is widely believed to have made its appearance around 50,000 B.C., so that was year zero for his count.

As more people began to move from a nomadic existence as hunter-gatherers to a more sedentary life as farmers, the world population grew at an increasing pace.

There is actually a specialty called paleodemography, and Haub drew on various estimates to come up with a population of around 5 million in 8,000 B.C.

George Johnson via Discover.