A Brief History of Everyone Who Ever Lived: The Stories in Our Genes

by Adam Rutherford

The truth is that we all are a bit of everything, and we come from all over. Even if you live in the most remote parts of the Hebrides, or the edge of the Greek Aegean, we share an ancestor only a few hundred years ago. A thousand years ago, we Europeans share all of our ancestry. Triple that time and we share all our ancestry with everyone on Earth. We are all cousins, of some degree. I find this pleasing, a warm light for all mankind to share. Our DNA threads through all of us. Ancestry is messy and difficult. Genetics is messy and mathematical, but powerful if deployed in the right way. People are horny. Lives are complex. A secret history is truly hidden in the mosaics of our genomes, but caveat emptor. No scientific test exists that will tell you where the DNA that you would come to inherit was precisely located in the past. Human history is replete with the fluid movement of people, and tribes and countries and cultures and empires are never, ever permanent. Over a long enough timescale, not one of these descriptions of historical people holds steadfast, and only a thousand years ago your DNA began being threaded from millions from every culture, tribe and country.

Genetically, two black people are more likely to be more different to each other than a black person and a white person. In other words, while the physical differences are clearly visible between a white and a black person, the total amount of difference is much smaller than between two black people. If everyone on Earth was wiped out except for one of the traditional racial groups, say, eastern Asians, we would still preserve 85 per cent of the genetic variation that humankind bears.

Tay–Sachs is not a Jewish disease. It’s seen at roughly the same frequency in Cajuns in Louisiana, and French Canadians in Quebec. There’s no such thing as a Jewish disease, because Jews are not a genetically distinct group of people.

August Weisman tested a similar idea in an experiment in which he cut off the tails of sixty-eight mice over five generations. Of 901 pups born, none of them was born without a tail. He wasn’t really testing use of a trait, but nevertheless was asking whether evolution might follow an acquired trait. Of course, as geneticist Steve Jones enjoys pointing out, the Jews have been performing a version of this experiment for a few thousand years, and so far a boy without a foreskin is yet to be born.

Are humans still subject to an evolution by the forces of selection? Yes we are, though its grasp on us is weakened and slowed compared to every other species in our 4-billion-year family tree. We are animals: we are special. Are we still evolving? The answer is unequivocal. Evolution is change plus time. We’ve seen it in our deep and recent past, sometimes demonstrably the result of positive natural selection, and often just an unopposed drift through time. An unchanging species is already extinct. As long as we keep making new ones, human beings most beautiful and most wonderful have been, and are being, evolved.

What a senseless phrase is ‘curiosity killed the cat’. To be incurious is to be inhuman. We did look inwards into the hidden kingdoms of anatomy, then cells, and now genes. We also looked up to the skies, and down into the ground and seas, and into the invisible worlds of the atoms, and subatoms, and now the quantum realm. We are the explorers, and science is exploration.