If you have been following this blog along with others, like GNXP, you can tell that the field of ancient DNA and population genetics is chaotic. It seems like every week we are adding more layers of genetic data in attempt to uncover the relentless and complex pattern on how we peopled the Earth. A Brief History of Everyone Who Ever Lived: The Stories in Our Genes by British geneticist Adam Rutherford is an introduction to the world of current population genetics for the layman. Think of it like a primer, a review, or summary of everything we know now. In the book, Rutherford, describes how our genomes reveal the sexual contacts of our ancestors with other hominids (Neanderthals and Denisovans in particular), and how culture, technology and disease have interacted and changed our genomes.
Speaking from the BBC studio in London where he hosts the weekly radio and Podcast program Inside Science, Rutherford gives us a rundown on the history of population genetics, and paleoanthropology. It kind of all started 2009, when DNA was extracted from the bone of a Neanderthal and now from that we have the whole genome sequence of a human species different from us. Since then we have found Neanderthal DNA contains Homo sapiens DNA and Homo sapiens DNA contains Neanderthal DNA. It got even crazier a year later, when the tip of a little finger bone and the molar tooth of a teenage girl were found in a cave in Russia in a place called Denisova. That proved enough to get the full genome out of this creature, which turned out not to be Homo sapiens, not Homo neanderthalensis, and not anything we were aware of!
We now call these people the Denisovans. They’re a human species but are not us, not Neanderthals, and not one that was previously known. We don’t yet have anything more than fragments of fossils. From the knowledged we have gained of ancient DNA studies, we know see that we interbred with the Denisovans, and they interbred with us. The further east you go today, the more Denisovan DNA you see in living people and the less Neanderthal. Interestingly, when you analyze the amount of DNA of the three species that we know interbred (Denisovans, Neanderthals, and Homo sapiens), it doesn’t quite add up, which makes us confident that we also carry the DNA of another human species for which we have no bones and no DNA. The shadow of another human species—its trace—is inside us all right now.
With this increasing granularity, we are seeing how genetics makes a mockery of race. The characteristics of normal human variation, the things we see and we use to determine broad social categories of race—such as black, Asian, or white—are mostly things like skin color, morphological features, or hair texture, and those are all biologically encoded. As we look into the full genomes from people all over the world, those differences represent a tiny fraction of the differences between people. If you take someone from Ethiopia and someone from the Sudan, they are more likely to be more genetically different from each other than either one of those people is to anyone else on the planet. There is more genetic diversity within Africa than in the rest of the world put together, making race not a thing, at all.