Visiting the relatives
David Reich is an ancient DNA expert who has written a book "Who We Are and How We Got Here". I wasn't sure if I wanted to wade all the way through the book. Fortunately, he has given a good summary in an interview (see link below for both).It is easy to think of human evolution as being some kind of smooth flow of development from an ancient ancestor in Africa to our modern form. But progressive developments in genetic analysis is opening up new perspectives on this.
At first, we thought of 'our stream' as being quite separate from the Neanderthals who we encountered. The Neanderthals had branched off from our ancestors in the distant past and established themselves in parts of Europe not yet settled by 'us'. On encountering our species, they could not compete and died out. These hairy cavemen could not speak due to a lack of structures in their head that enable speech. They could only grunt, like primates.
But genetics established that, far from dying out, 'our' branch and Neanderthals had interbred and we all, with some exceptions of groups who stayed in Africa were 'part-Neanderthal'. So, the picture changed from one of the complete removal of one group to an 'overlay' of 'new blood'.
Not longer after the Neanderthal discoveries, new ancient species of humans were found in many locations across Asia and Oceania - denisovans, habilis the tool makers, erectus large brain, ergaster, floresiensis, heidelbergensis, rudolfensis, antecessor. Clearly, the branches of 'homo' were many and varied and emerged quite independently in time and location.
So, why are we the sole survivors. Reich believes that it just turned out that way. As waves of one type swept across the landscape, either the less competitive species was extinguished or subsumed. This happened again and again until modern humans remained.
Variations in modern humans was no more 'organised' than the competing ancestors. Some groups in isolation became distinct, to their ultimate detriment. Other welcomed diversity and thrived.
It might be intuitive to think that the human genome and the ultimate survival of 'our' line was a product of inter-breeding and one group dominating anther, probably violently. Was it survival of the strongest? The most populace?
Reich reveals what ancient DNA tells him and us. The arbiter of who lived and died was the plagues that beset nearly every population in nearly every era. Plagues changed the dynamics of power and fortune dramatically. This might give us pause for reflecting on the 'plague' we have lived through. Has the impact on our economy and our modes of living been irrevocably changed such that the centres of power will collapse?
Reich gives us no answers to these questions. In fact, the interview is really about asking the questions that are likely to frame future study.
Interviewer: If you're right that a lot of the brain size had already been accumulated before this with Neanderthals, then they should have been pretty smart hundreds of thousands of years ago. But they're not expanding out. Then something happened 60,000 years ago. Then this group that descended from the people in sub-Saharan Africa just explodes all across the world. Something seems like it changed. What do you reckon it was?
Reich: This is outside my area of expertise. I'm being very much like a scientist right here. I'm very sympathetic to the idea that it's hardly genetic. I think that this is cultural innovation. It's very natural to think that this is cultural innovation. Humans sometimes develop a new technique of storing information, sharing information, and so on. For example, writing allows you to record collective knowledge in a library, computational knowledge, large storage devices, and so on and so forth. Language, conceptual language, allows you to create a cultural body of knowledge.
There is plenty to chew on in this 2 hour interview, including origins of the caste system and whether agriculture was responsible for disease. It's well worth the viewing.
Links:
David Reich – How One Small Tribe Conquered the World 70,000 Years Ago
Citations:
Reich, D, Who We Are and How We Got Here: Ancient DNA and the new science of the human past, OUP Oxford, 27 Mar. 2018, ISBN-10 : 9780198821250