Homo hybridus
We are all hybrids
Olga Orlova, "Trinity Variant"
Why are there only us Cro-Magnons left of all the kinds of people who existed on Earth? This is an important question, the answer to which would give us an understanding of how humanity will be able to survive in the future, and it has become one of the central ones in the new book "Human Evolution. Bones, Genes and Culture" (Corpus, 2022), written by a married couple consisting of doctors of Biological Sciences — Head of the Department of the Faculty of Biology of Moscow State University Alexander Markov and ved. nauch. sotr. Elena Naimark of the A.A. Borisyak Paleontological Institute of the Russian Academy of Sciences. He talks to them about it Olga Orlova.
Olga Orlova: So, you have already published the third book devoted to human evolution — "Bones, Genes and Culture". And in it, as in the previous two (Human Evolution. Book 1. Monkeys, Bones and Genes; Book 2. Monkeys, Neurons and the soul), presents new knowledge about ancient people. However, at the same time, there is a lot of information about ourselves in the book. For example, I was struck by a fact from a 2020 study that got into this book. You write that geneticists have discovered a section of the genome in humans that increases the likelihood of severe covid by two times. And it turned out that this part of the genome belongs to Neanderthals. Moreover, what is strange if in Africa and It turns out that there are quite a few such people in East Asia, then in Europe they are already 8%, and in Bangladesh as many as 38% of such people. And this is far from the only thing that is told to us about our ancestors, but at the same time it says something important about ourselves. And what other knowledge about ancient people in the process of writing this book turned out to be a revelation for you about our modernity?
Alexander Markov: Thanks to the achievements of science, especially such a completely new science as paleogenetics, in recent years we have learned an amazing lot about our origin, about our history. Now science has invented such methods that allow us, quite unexpectedly for all of us, to penetrate into the secrets of the deep past, our past, where, as it seemed, it would never be possible to look at at all.
Elena Naimark: Personally, while working on this book, I was most surprised by how quickly knowledge in this field of science is accumulating. Right at some magical speed. And, in addition, the appearance of an incredible number of some magical methods that allow you to say things that could not even be imagined before. The hypothesis of human origin — in Africa or in Asia? Where did humanity originate? Previously, we thought, based on the data on anatomy and paleoanthropological findings, that, most likely, it would be Africa. This hypothesis about the exit of modern humanity from Africa has been dominant for decades, but in the last five years a huge amount of new data has appeared that demonstrate the great diversity of humanity in Northeast Asia. Why there? Because we just didn't know how to test this hypothesis. Now we have such an opportunity.
O.O.: Does science allow it now?
E.N.: Now we have time to test old hypotheses, new hypotheses, and compare them, and this is amazing.
O.O.: There is a topic related to hybrids in your book. You give various examples that suggest that Denisovans, Neanderthals, and Cro-Magnons interbred with each other. For example, Danny from Denisova Cave is described as a hybrid of the very first generation. Her mother is a Neanderthal, and her father is a Denisovan. According to other findings, it is clear that Sapiens, Neanderthals and Denisovans met, interbred, in general, these crosses constantly occurred on the territory of Eurasia, and then it did not go further. Why?
E.N.: It's probably not quite right to say that things didn't go any further, because we are all hybrids. About 2-3% in some populations, 7% among the peoples of Southeast Asia, Papuans - they generally have a lot of these same impurities. Humanity in general is prone to interbreeding. If there is a place and time, then there will definitely be some crosses. And depending on whether these species, subspecies or forms are close, some kind of genetic heritage will remain in the descendants. The fate of this legacy depends, of course, on the quality of genes, on drift, on many, many genetic factors, but why not stay with us, if there are some genes that protect against diseases, why not save them from this alien import? Of course, let's keep it.
O.O.: Wait. Here is the section from the Neanderthals that now gives people a severe form of covid, on the contrary, it is harmful.
E.N.: Well, there is also some form that gives us immunity, including innate.
A.M.: Viruses evolve very quickly, new ones appear all the time. And the immune proteins that protect us from these viruses are also evolving very quickly. Therefore, different populations have a different set of these proteins.
O.O.: So the piece that was left from the Neanderthals, at some point, on the contrary, protected us from something?
AM: That's right, he was protecting against some other virus, which, apparently, was especially plentiful somewhere in Bangladesh. And in China, for example, may have had coronavirus epidemics before, in some former times. And there this Neanderthal variant, harmful, which does not help well from the coronavirus, may have been eliminated by selection, so it is not found there, in China. And there were some other viruses in Bangladesh, where the frequency of occurrence of this Neanderthal variant increased. After all, the mixing of gene pools occurred rather unevenly. Non-African humanity received 2% of the genes from Neanderthals, and 98%, sorry, from Sapiens. Somehow, it's very uneven. And geneticists have shown that when this hybridization took place — somewhere in the Middle East about 55 thousand. years ago, the most important hybridization of Sapiens with Neanderthals happened — at first there was more Neanderthal DNA in the population of our ancestors than now — not 2%, but 3%. But a significant part of these impurities were harmful to us and were eliminated by selection. And, characteristically, the more important a gene is for human life, for development, the less Neanderthal inclusions it has on average. And in the least important parts of the genome, on the contrary, the maximum amount of Neanderthal impurities was preserved there. What does this mean? That our species, Sapiens in Africa and Neanderthals in Europe and Western Asia, have lived separately for too long and they have accumulated in noticeable quantities poorly compatible genetic variants. Hybrids could appear: they met, crossed, hybrid offspring appeared. But this hybrid offspring, on average, had reduced fitness compared to pure forms. This partial genetic incompatibility, which has already been, apparently, is the main reason why, having met, Sapiens with Neanderthals and Denisovans did not merge completely. And those others, after all, died out, and we survived, retaining 2% and 5% of their genetic admixtures.
E.N.: But then, when this humanity arrived on the territory of Eurasia and began to actively explore it, there began a constant mixing, separation, differentiation and hybridization of everyone with everyone. For example, let's take the European population, it is closest to us. How do we imagine this? Here we have a tall blonde, if we talk about a man, or a blonde with blue eyes, with light skin, all that sort of thing. And we imagine that this is the population of Northern or Eastern Europe. But in fact, this type is a product of mixing very many migration waves. Where did we get blonds from? And they came from the territory near Lake Baikal, this is Central Siberia. That's where the blond hair gene appeared.
O.O.: Who would have thought of that today?
E.N.: Who would have thought that our blondes — they come from there, from Baikal? Or from the territory of Lake Baikal, so to speak. We know that all modern Europeans have more or less fair skin. Was she like that? Nothing like that. It was introduced by the migration wave and is a product of hybridization with people who came from the Black Sea region, from the Caucasus, with the culture of the so-called Yamnik, who invented carts, harnessed horses to them and went to travel all over the Volga steppes and further east. And as a result, they ended up somewhere in the north of Sweden, Germany, and some other current countries. Last of all, they gave birth to the Celts in Britain. This is the last territory they inhabited. And how can we say who we are now? Now there is no idea of rigidly fixed races, but there is an idea of constant displacement, mixing and the formation of new and new hybrids.
O.O.: Let's go back to the key question related to human evolution. We started with the fact that there were many ancient types of people, but in the end only we remained. We have displaced the others. Still, why?
A.M.: A terribly interesting and important question, indeed. It would seem that when all this was happening, in the Middle Paleolithic, Sapiens, Denisovans and Neanderthals had about the same level of development, well, give or take. It was, as they say, the Middle Paleolithic. Similar stone tools — similar in level of complexity, technology of making stone tools. Some glimpses of art, some decorations, the use of paints were already beginning to appear. This was all the case with Neanderthals in general, and with Sapiens in Africa.
O.O.: So the chances were equal?
AM: They were close, at least it would seem. But something happened. And something still gave an advantage to one of the three species, namely the sapiens that came out of Africa. And there, just at the time when the Sapiens ousted everyone, 40-50 thousand. years ago, there was a great cultural revolution among the Sapiens, this Upper Paleolithic revolution, when suddenly culture began to develop much faster than it did before. There are paintings, flutes, much more complex composite tools. A cultural explosion begins. Why? Why is it exactly with Sapiens and at this time? Maybe it was the Sapiens who, in the course of cultural evolution, first developed something in culture that allowed several groups to agree, somehow unite. That is, Neanderthals seem to have lived in small groups. A group of hunter-gatherers cannot be large, because a large group is simply not able to feed itself by hunting and gathering. The groups were necessarily small. But these groups could all be at enmity with everyone, eat each other, kill, compete for any reason, and could, on the contrary, change brides and grooms, remember family ties and somehow coordinate their own actions. For example, if we worship the same idol, speak the same language, then we seem to belong to the same community. Perhaps the ability to unite several groups of hunters, to gather in some larger community like a tribe, first appeared in Sapiens. And this would, of course, give them a huge competitive advantage over other species that were represented only by disparate warring groups.
E.N.: It seems to me that another interesting fact can testify to the commonality of culture, which has become known only very recently. There was a study of rock carvings all over Europe and in general all that there is, the entire pool of these rock carvings. It was not the rock carvings themselves that were studied, but the signs that accompany them. Crosses, some lines, zigzag or smooth lines, some icons, circles with hooks. So, it turned out that there are very few such types of accompanying signs, about thirty types. And interestingly, they are uniform in all drawings, in all caves, in all locations.
O.O.: And this is not only in Europe?
E.N.: Everywhere. And it's amazing. Anthropologists make a very cautious assumption that these may be the beginnings of some kind of proto-symbolic writing or a reflection of some symbolic language. But the fact that they are the same everywhere suggests that this people was able to unite and use some common symbolic signs.
AM: There is also a line of thought such that this advantage of sapiens, which allowed to displace all other species, was due to some unexpectedly rapid development of the language. Here is something in the speech, in the language has changed. Noam Chomsky has long been developing these ideas and a number of other scientists — that the advantage of sapiens was somehow connected with language. Whether there was some kind of this grammar universal - not universal, innate — not innate, but the ability to build some specific relationships between statements that can be very different and can be nested, i.e. you can say "I see a cat", you can say "You know that I see this cat", or you can say "Vasya remembers that you knew that I see this cat." And so indefinitely you can create a variety of designs. That is, if you know how to say "Let's go hunt a deer", and there is a word for a mammoth, then you can easily say "Let's go hunt a mammoth". And maybe the Neanderthals, let's say, haven't had that yet. They had some more primitive language, for example. And most importantly, our brain was the same size as the Neanderthals, but different in shape. The dynamics of development in ontogenesis, in childhood, is different. Our brain is different from the Neanderthal brain.
O.O.: You named two versions. Maybe one accompanied the other? This ability to unite and the ability to some kind of common communication system. And this arose because the Cro-Magnons had a slightly different brain, different from the Neanderthal, or vice versa, the Cro-Magnons' brain became different because some new neural connections were formed, because they could unite, they had a common communicative system of signs? What is primary here?
AM: This is a chicken and egg problem. This is a single process, inseparable, coevolution of the brain and culture. That is, the evolution of the brain affects the development of culture, the development of culture simply affects the evolution of the brain with the most terrible force. This theory, which in recent years has begun to enjoy great attention among anthropologists, is well deserved.
E.N.: There was a study devoted to complex tool activity, when, for example, we need not just to hit another stone with a stone, but to take a stick, tie some kind of chopper to it, and with this stick we can split an object very accurately. This stick with a chipper attached is a composite tool, and it is much more difficult to use it. The brain had to adapt to the use of such complex objects. To do this, some new circuits were improved in the brain and, perhaps, some new circuits were installed. Interestingly, when analyzing complex linguistic constructions with subordinate sentences, which Alexander spoke about — such as "I know that you saw a cat that Vasya saw, who drank milk" — and when using complex composite tools, the same circuits are activated in the brain. That is, everything grows from a single root. Not the root, but, one might say, the nucleus in our brain, which somehow began to serve such a complex activity.
O.O.: So now teachers or parents can tell children: "If you don't read big and fat books, you'll turn into a Neanderthal, you'll come back"? Well, indeed, the book leads to this, ends with this complex link of the role of culture in the development of mankind with the evolution of man. On the other hand, we are now seeing the opposite effect. I just wanted to remind you about one film, it recently appeared, made a lot of noise, it was often discussed. This is a tough satire, a dystopia, one can say, very sad, the film "Don't look up" — "Don't look up"2. The story of how astronomers discover a ten-kilometer comet flying to Earth. A collision with our planet means a catastrophe, the destruction of all earthly life. There is half a year left, and now scientists are trying to reach humanity. However, a society whose modern cross-section is shown with all ruthlessness, on the one hand, is able to calculate the trajectory of the comet and technically prevent this catastrophe, and on the other hand, it is completely incapacitated in intellectual terms. People cannot escape for a thousand different reasons — they underestimate the danger, they are busy with some other things. And it turns out such a paradox that technically people can prevent this catastrophe, but their culture does not allow it. And at the end of the film, the main character, an astrophysicist, played by Leonardo DiCaprio, says sadly: "We had absolutely everything, if you think about it." As a result, people are dying. I want to ask, how do you like this paradox: first, culture allowed us to rise, and now it turns out that it brings us back to some deep archaic past?
A.M.: Yes, it's a good movie. And it's really terrible, Elena Borisovna couldn't even watch it in its entirety from the first time, it was so terrible.
O.O.: Why?
E.N.: Hopelessness, this hopelessness is killing me.
A.M.: Yes, this is despair.
E.N.: Desperate hopelessness is killing me.
O.O.: Was it hard for you as scientists to watch it?
E.N.: It's a shame for humanity.
AM: On the other hand, as paleontologists, we must understand that mass extinctions have happened many times. And not even all the people died there, you saw.
A.M.: Cultural evolution, according to many experts, is a largely blind process, just like biological evolution. This is a natural process that follows certain laws of its own. We are a unique species of animals, because we develop precisely at the expense of culture. Other species have rudiments of culture, other animals have small rudiments of culture, but only we have the process of coevolution of genes, brain and culture entered such a self-sustaining autocatalytic phase and fired. He made us what we think are reasonable. But that's probably all in the past. The process has exhausted itself, we have achieved complete domination on the planet. Intergroup cultural selection is an important process that prevents harmful, parasitic aspects of culture from developing in groups. But when there is a weakening of intergroup competition, globalization, when some empire, for example, the Roman Empire, achieves dominance in gigantic territories, it does not have external enemies, culture begins to degrade. This is a completely natural process.
O.O.: So the story that is presented and described in "Don't look up", for example, does it look quite real and convincing from the point of view of cultural evolution?
A.M.: Absolutely. Yes, yes.
E.N.: Well, I would probably add something to what Alexander said. Our cultural evolution still functioned in small groups. We have never been as numerous as we are now. And the quantitative factor becomes very important. Our culture just doesn't know how to work with such masses yet. Our numbers are now becoming the most important evolutionary factor.
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