People’s fascination with genealogy is nothing new, but modern biology has seemingly made possible an exact breakdown of the DNA of our ancestors. Apart from the questionable precision of some of these ancestry reports, what this cultural phenomenon reveals is a deep thirst to be able to tell a story about ourselves. But that story is almost inevitably a selective narrative of our past rather than an accurate representation of our biological history, writes Eviatar Zerubavel.

Why do we consider Barack Obama a black man with a white mother rather than a white man with a black father? What are the implications of knowing, as we now do, that chimpanzees are genetically closer to humans than they are to gorillas? Why did the Nazis believe that unions between Germans and Jews would produce Jews rather than Germans? Are sixth cousins still family?