Our closest common ancestor

is closer in time than you think it is. From Scientific American:

In 2004 mathematical modeling and computer simulations by a group of statisticians led by Douglas Rohde, then at the Massachusetts Institute of Technology, indicated that our most recent common ancestor probably lived no earlier than 1400 B.C. and possibly as recently as A.D. 55. In the time of Egypt’s Queen Nefertiti, someone from whom we are all descended was likely alive somewhere in the world.

The mechanism here, which is intuitive as soon as you understand it is that the number of branches in your family tree grows exponentially as it goes backwards. But that’s not all:

“Branches of your family tree don’t consistently diverge,” Rutherford says. Instead “they begin to loop back into each other.” As a result, many of your ancestors occupy multiple slots in your family tree. For example, “your great-great-great-great-great-grandmother might have also been your great-great-great-great-aunt,” he explains.

Some other surprising estimates from this article:

• It is estimated that everyone alive today in South America has at least some European ancestry

• It is estimated that “nearly everyone of Jewish ancestry has ancestors who were expelled from Spain beginning in 1492”

Via Max Roser