How to Argue With a Racist: What Our Genes Do (and Don't) Say About Human Difference

by Adam Rutherford

Go back a few centuries further and we reach a mathematical certainty referred to as the genetic isopoint. This is the time in history when the entire population is the ancestor of the entire contemporary population today. For the people of Europe, the isopoint occurs in the tenth century. In other words, if you were alive in the tenth century in Europe, and you have European descendants alive today, then you are the ancestor of all Europeans alive today (we estimate that up to 80 percent of the population of tenth-century Europe has living descendants). Another way to think of it is like this: One branch of a family tree of two first cousins crosses in a shared grandparent; one branch of all European family trees cross through one individual in 1400 CE; at the isopoint, all branches of all family trees cross through all people for that population.