Why Is There Only One Species of Human? - Robin May

So for those of you who have attended my previous lectures in this series, we've been talking a lot about the kind of foundations of evolution, so what is evolution, what are mutations, what is the role of chance in evolution tonight? We're going to change direction and get a lot more personal and just think about evolution in the context of ourselves and in particular the question I want to ask and I'm going to give you a spoiler alert. I'm not going to answer it, um. The question I'm going to ask is why are we alone on the planet, why are we the

only

human

species

and I think if you think about that in such a fleeting moment, you might think it's a completely trivial question, but actually it's not so trivial, and for those of you who are sci-fi fans, there are a lot of great sci-fi movies where you see your hero walk into a bar and there are all these different

species

in the bar. chatting in various languages ​​and ordering drinks um and in fact if you look around the world there are many cases where very, very similar species live alongside Jou um, but as far as I can tell tonight, at least in this room, um if I look around the room I think we're all

human

uh no one's intruding from a different species here and it's not inconceivable to have some kind of parallel planet where we were a mixed species right, I could be giving this talk in multiple languages ​​to multiple different species, all bipedal, relatively intelligent ap-like organisms, um, and they interact with each other, but we don't live like that, so something has happened to make humans the

only

human species on the planet, um and uh, no we know the answer. why, but what I want to do tonight is think a little bit about how we got here and maybe speculate a little bit about the factors that might have driven that evolution and maybe even in the future think a little bit about where we might go from here .

Before we think about why we are the only species, it's very important to think about what a species is anyway, and that's actually not a very simple W question to answer. There are several definitions of what a species is, but perhaps the only one. The most used and most functional is the one proposed by Ern Meyer, who you see here, which is known as the biological species concept, which in essence says that a species is a group of individuals that reproduce together successfully and is important. say successfully, then it's not just about the ability to reproduce, but the ability to do so in a way that maintains the species, so if most of your descendants die, for example, then that's actually not a successful reproduction, it must be able to reproduce. successfully and that group is reproductively isolated from other similar groups, so in other words, you are not reproducing with other species, you are distinct entities and, as we will see later in the lecture, that is actually quite complicated. to define and quite problematic. particularly in the case of humans, but I still think that it is still probably the best example or the best definition that we have of a species and by that definition, Homo sapiens, our own species, is in fact both things that we can all reproduce together um, and there is no Another species with which we reproduce the Gresham College lecture that you are listening to right now gives you the knowledge and insight of one of the world's leading academic experts, so it takes a long time, but because we want to encourage the love of learning.

We think it's worth it, we never make you pay for lectures, although donations are needed, all we ask in return is that you send a link to this lecture to someone who you think would benefit and if you haven't already, do Click on the follow or subscribe button. wherever you're listening now, let's get back to the lecture and that in its own right raises an interesting question and the question essentially is not why we are just one species, but why don't we have another sister species that looks like a They look a lot like us in the planet because many animals and plants do it.

For example, if you are a lepidopterist, if you like butterflies, you will be familiar with these types. These are the Heliconius butterflies and they are a complete Nightmare, huh, because they all look the same, but there are actually many different species, in fact, in this particular diagram, each pairwise comparison is two different species and I don't know, but It is certainly very difficult for me to tell you. They are separate and yet they are distinct, so there are many sister species in this genus and the same applies to many other animals, so I am a bit heavy, not very good and definitely not good enough to tell them apart . these are Clarks and Western GRE or possibly Clarks and Western GRE depending on which direction they are facing um and these are two distinct species of birds uh and yet they are almost impossible to distinguish in the field and in fact these are an American Species In the North, but closer to home, for example in the UK, we have the marsh tit and the willow tit, and you have to be a fairly advanced ornithologist to be able to spot the difference between those two species in the field, so What there are There are many examples of species that are very similar and that live relatively close to each other and yet, we do not walk down the street and enter the supermarket and see something that looks like a bipedal, hairless, intelligent ape, but which is actually not a human, as far as we know, we are alone or we are.

I mean, the first question maybe is whether we've missed something and one of the things that people occasionally speculate about in the press is that maybe we've missed another related species of humans and actually, it's not completely impossible to think in that because even today in the 21st century, in this kind of very developed world that we live in, there are large areas of essentially unexplored wilderness, so in fact, in this 2018 estimate, almost a quarter of the world population. The land surface is still classified as wilderness, meaning it has relatively little habitation or human activity shown here, so perhaps it is possible that there are other species living in these wilderness areas although of course even the wilderness areas are visited relatively frequently by tourists or explorers or Mountaineers or whatever, it seems a little unlikely that there would be large populations of another human being living in those places.

There are some parts of the world, of course, that are completely unexplored and according to recent estimates it is around 2 or 3%. of the world's land surface hasn't really had human access to it, so of course it's possible that there are other species hidden away. The problem is that those 2 or 3% of the unexplored world are largely things like remote mountain tops, in the middle of Antarctica, places that are not compatible with human life or at least human life as we know it now. . It's possible, of course, that there are some species that can live in the middle of Antarctica and wander around happily there and we don't know about them.

Um, but they would look quite different to modern humans. I think it's pretty unlikely that they exist. Never say never, but I'm going to bet some decent money that there probably isn't a second species of humans that we don't have. discovered yet, so what about the second possibility? Perhaps there is a second species lurking right under our noses, and in fact, if you were an alien approaching this planet and looking at the fantastic diversity of humans on it, you might reasonably think that this is not the case. In one species, we have all kinds of different shapes, sizes, colors, cultures, societies, and family structures, and we do all kinds of different things.

I think if you looked at it in another species you could reasonably think that they represent different groups of people and this, of course, was something that early explorers, European explorers in particular, floated around as ideas and, in fact, even quite late in our kind of exploration of the world, people speculated about this, so this, for example, is a picture of Charles Darwin. He came to South America on his trip on the beagle and when he got there in his diary he recorded many interesting interactions, one in particular with the native population of Tiara Del Fego, the fanatics, and in his diary at that time he noted this .

He said that seeing these men one can hardly believe that they are similar creatures and inhabitants of the same world. I came up with this suggestion that maybe they were different and this, of course, this pseudoscientific idea was the horrendous justification used for real tragedies like the enslavement of people in Africa and the eradication of Native American populations, um, in a deliberate genocide by part of the Europeans, the point above all. Although this is completely false, we know and actually knew from the beginning of Europeans' first interactions with native populations elsewhere that we are one species, whether through coercive or sometimes consensual relationships.

We knew that people could have perfectly successful children together and In fact, one of the great revelations of the complete sequencing of our genome today is that many of us, perhaps even in this room, realize that we have a very interesting genetics of all kinds of populations from the past because, as we now know, all humans around the world. world we are one species and we can reproduce together, so we are not overlooking any secret second species within our own group, um and uh, so we also do not have a hidden species somewhere else nor are we overlooking something here, there is a third possibility and the The third possibility is that we may be overlooking a sister species that we talk about all the time, so, as you well know, hopefully we are great apes and, along with the other families of species with the great apes, we all share many characteristics and our closest relatives, as I'm sure you know, are chimpanzees and bonobos, so maybe I'm here saying that we're alone as a species and I'm talking nonsense because maybe these are our sister species and that is a possibility that they seem. a little bit different than us, they're a lot hairier to begin with, but they're actually very, very similar and in fact from genetic data we know that we share something like 98% of our genome with chimpanzees, that's pretty high, So perhaps chimpanzees are actually a sister species to humanity, however, if you look at that level of genetic preservation within humans, the amount is much more consistent, so it's typical, in a room like This, a typical human to human comparison shows 99.9% DNA. identity and even the most diverse humans still share something like 99.6%, so the differences between any two humans in terms of genetics are an order of magnitude smaller than the differences between us and chimpanzees, perhaps most importantly is that chimpanzees, of course, have a sister species, the bonobos, and if we look at them, the genetic distance between them is approximately 4%;

In other words, the difference between a chimpanzee and a bonobo is about the same as the difference between a human and a quite different human of the same species, so these two are in fact sister species. but they are not a direct sister species to humans, the distance is much greater, so no matter which way you look at it, whichever way we take this question, in fact it seems that we are alone, we are the only species of homo the genus the one we're on, uh, which is currently on the planet, so maybe there's not a problem here because maybe in reality we've always been alone, maybe homo came into existence um and we've been a solitary species essentially for our entire life. history um and This question or this suggestion I guess was unproblematic for most of human history, because, of course, for most of human history, certainly in Western Europe at least the predominant rhetoric has been that of biblical creation, so the idea that humans were created as one species has dominion over all other species, so it would make sense from that particular point of view that we were alone because if you are going to create one species to dominate all the others, you probably wouldn't create two because that's going to be problematic, um, and until about the 18th century, this wasn't a particular problem;

However, as Darwin's theory of evolution by natural selection took hold and people began to really understand this principle, they began to increasingly question this idea of ​​why humans should be so different from everything else if species arise by natural selection through diversification so why should human species be different from others? Why haven't we diversified? Why don't we have these sister species and this problem, I guess, was particularly rumbling? in the more learned liberal Victorian society, at least in England at the time, and indeed in many of the learned cities of Europe in particular, and people began to ask questions about some of the artifacts that had previously been reportedparticularly. from mining expeditions and in fact for many decades people searched for stone for buildings for example they had occasionally come across weird and wonderful things that we would now call fossils or archival material sometimes these were animals often they were animals um but They frequently came across things that looked quite human, for example like this skull excavated from a quarry in Jalta in the early 19th century, when they did that the scientific community typically described them as at least archaic humans, so they were humans who have existed. uh for a long time uh there was also something interesting and slightly funny and quite disturbing in some ways uh a kind of exchange if you will, these things were associated with crazy myths, so people say that they are extinct giants um or they were some kind of mythological beasts with heads of 12 or something like that um and there was a sort of roaring circus trade in demonstrating fragments of terrifying monsters that came out of quarries um however we now know scientifically that that was not true um so these things had been found over a period of time but they had always been attributed to Homo sapiens, so people would say These are old archaic humans dead long ago and then in 1856, this part of the skull was found in Germany, in the Neander Valley, and a master of German school successfully identified it as sufficiently distinct from Homo sapiens to be a different species and this. is the species we now know as Neals and once that view was promoted that this was a different lineage of humanity, people went back and looked at other material, including this jalter skull, and realized that this skull was actually much more. similar to this nandal skull than to modern humans and, actually, much of the fossil material that had previously been identified was now found to be nandal material rather than human material, so this, which is also happening in the context at At the same time, for example, when Darh was publishing his book On the Origin of Species, he was entering into this kind of very intellectual debate about the diversification of human evolution, although it didn't really change our view that humans are a species. of solitary species in existence um however in 1891 this rather handsome fellow here with the uh with the nice mustache Eugene DUIs who was a Dutch anatomist was working in what was then the Dutch East Indies now Indonesia um and was particularly interested in some of The remains were found in caves as people moved forward and, in particular, the logging industry when they began to wander into the rainforest, they sometimes came across caves with remains of bones.

He began collecting some of these and sorting them together and realized a collection of skeletons. material um belonged to something that looked very human actually misidentified it and thought it was an extinct species of great ape gave it a different name and published it but people once it was sent back to Europe did not agree with this um and relatively quickly I realized that this was a second example of a different species of a now extinct human-like organism. So within the genus Homo and this is what we now know as Homo erectus, a long extinct ancestor of modern humans and for which there is now fossil material. from many other places around the world, so now that we are approaching the end of the 19th century, we have a position where there are at least two species of Homo so nealis um and what is now Homo erectus that we believe have existed and no longer exist , so the world is starting to look at the fact that maybe we haven't always been alone through quite a different lens, and then this third piece of the puzzle, if you will, shows up in 1907 with this guy.

With even sleeker facial hair, beards are getting longer all the time. I think this is Oto scac and he was a German industrialist and I really like this story because actually, when he was a relatively young man, he was a chemist and he settled down. He created factories that essentially produced chemicals and made a lot of money. He was essentially an industrial entrepreneur. And instead of buying himself a, I don't know, you know, fancy yacht or something and sailing around the world, he decided to invest his money. with a proper education, he went back to university and studied what was then known as prehistory, what we now call anthropology or something, um, and used his money to fund research into the evolution of humans and, in particular, what he would do .

A reward was offered to people who worked in quarries in Germany, if they found any interesting material, they would take it and he would pay them for it and in 1907 the ma Quarry um someone came to uh Otto with this quite spectacular Jawbone um and also in his new life as a paleontologist um he correctly identified this as another species of homo and another extinct this is what we now know as homo heidleberg Enis named after him and at that time it was the first really well accepted totally different species of humans since 1907, obviously we have had a massive explosion in activities, particularly in the last 20 or 30 years, actually in the discovery of fossil material and artifacts associated with humans, um, and this is an incredibly fast-moving field.

So actually, in the time that I've been talking to you, I'm sure someone will say that I'm completely wrong, um, uh. So to avoid everyone blaming me, I grabbed this rather nice diagram from the Natural History Museum. so you can blame them for being outdated, we now know that there are many now extinct species of homo that have existed and have existed in parallel, so for example here in the top corner you can see at least four or five species that have been present on the planet at the same time for a large period of our history, but they are no longer present with us today, as far as we know, as I said, Homo sapiens is the only one of them that is still present so why might it be What has happened to drive this colonization of homo sapiens around the world and eliminate these other species?

Why don't we go to the supermarket and come across a homo hydal bensis and think about that? In a little more detail, we need to think about what our most recent parallel species were like and why they may therefore no longer exist now, as far as we know at the moment and, as I say, this is certainly subject to changes and I suspect that very soon we will have to revise this lecture, but as we know at this moment there are at least four parallel species of homo likee organisms so similar to us that have coexisted in relatively recent evolutionary history and by relatively recent I mean the last 100,000 For more or less years there are cells, this is homo sapiens and it looks like a very familiar skeleton, and then the species that we know the most about, by far, are these guys and the annals, in many ways, a very, very similar, looks very similar, same type of bones.

Thicker you can see, the bones are thicker, the whole body is more developed, uh, and some subtle differences are particularly around the skull and the example that I like the most is that people say that you can tell if you are a nandal or a homo sapiens. standing in the rain, so if you are outstanding in the rain and the rain is forming a nice layer in front of your eyes because it is dripping from your forehead, then you are probably an andal and you should look in the mirror, um, if so . running down your face and dripping from your chin, then you're probably a homo sapiens, you can go home safe knowing the right species, uh, because Nean had a very prominent forehead crest and a receding chin, we have a negligible forehead crest and a protruding crest. chin so you can check your chin now in the audience if you want to make sure you're the right species and if not, please come see me later because it really ruins the conference if you're a Neal um so these so we know. a lot about the Neals we have a lot of fossil material and we have a lot of artifacts associated with their life and as I'll show you in a minute we also have genetic information so we have this little guy here this is homo floresiensis um we know a lot less about this species for two reasons, firstly, it was only discovered in 2003 uh and secondly, we have only found it on the island of Flores in Indonesia and nowhere else um and people with good memories You may remember that the kind of media hype around this is often referred to as The Hobbit um because as you can see from this it's very small in fact homo fenis uh probably maxes out at about a meter in height so here somewhere like that um it was a very species tiny of homo and people still argue a lot about where it fits, it has some features that seem very ancient, much more like some human precursors, if you will, who lived perhaps 6 million years ago, but in other features it seems relatively modern, much more similar to Homo sapiens and its lineage is not clear.

There is also relatively little fossil material of this species. There have been some difficulties in studying it, so the position of floresiensis in the family type. There is debate about the tree, however, the dating is pretty good, so we know that this guy was running around the island of Flores at the time when modern Homo sapiens were in other parts of the world, so it is certainly contemporary in time, even if it wasn't. contemporary in geography and then the fourth and final species that we know we've shared our planet with relatively recently um it's significantly unspectacular as a fossil uh because here it is uh these are the Denisovans and the Denisovans are a pretty mysterious species that lives in Asia in Siberia in what is now Russia essentially um and to date uh this is pretty much the full extent of all the fossil material, although we do have a little bit of arm or leg bone, a little bit of jaw and some teeth from various individuals. uh, so it's quite difficult to reconstruct this, all the data we have suggests that they were probably similar in type of physiology to uh, you and me, so simple that we are not very small, for example, like the Flores species um, um, that we know.

We date that they definitely existed at the same time as Homo sapiens, so they were present at the same time and we know that they are distinct from both us and the annals, so we have at least four species that cohabited the planet at the same time and our best assumption is the wrong phrase our best information so far suggests a story that looks a little like this and I'm going to caveat this by saying um, every time someone discovers new fossil material, all the dates change and many of the migration patterns change, so if you're watching this to catch up in six months, I could be completely wrong, go ahead and do a Google search, but as of today, this is our opinion, the opinion is that, uh About 600,000 years ago, homo hyal beige, you will remember that it is the Jawbone that was reported from Germany.

It was a more recent common ancestor species of modern humans that evolved in Africa about 600,000 years ago and then, from its African origins, began to migrate. uh, in Europe and ultimately in Asia, once located in those parts of the world as species do and as those of you who attended previous conferences will remember, um, it began to diversify and began to, in the process normal evolution, accumulate mutations, accumulate phenotypic changes, so physical change and natural selection did their job, the fittest organisms survived and the unfit ones became extinct, so, for example, the environment in the north of Europe, as we know it, is quite different from that of central Africa, not least, it was much colder and, therefore, the selections.

We began to act on this and ended up diversifying into what we now recognize as a new species and the annals, at the same time, these early pioneers in Asia we are also under selective pressure, we are also diversifying in a different direction. um to become what we now recognize as Dennis ens, so those are the three and then the fourth species that I mentioned, we know very little about here, he's down here, homop forensis um, we know from the dating that they were present in Flowers approximately 74,000 years ago we don't know at all how they got there or where they got there from, so we don't know, for example, if they are direct descendants of any of these groups, or some kind of parallel evolution, or some kind of very mysterious migration from a different part of the world, but they were still there, so if you had dropped on the planet, say, 60 or 70,000 years ago, and had a bird's eye view, you would have seen these different populations in these different parts of the world.

Meanwhile, the world in Africa, Heidleberg in this, of course, does not remain unmoved. Evolution continues to work even if you are in the same place and continues to select for traits that are beneficial, in particular, such as greater intellect, the ability to do things.like using tools to coordinate hunting activities and ultimately doing all the things that make humans so successful. These selective pressures change the appearance of Hydes and ultimately lead the evolution of what we recognize as a different species, namely the anatomically modern Homo sapiens. modern humans um and the date of this emergence of the first humans um has moved many times even in recent years uh we now think that anatomically modern humans were present in parts of Africa about 300,000 years ago, particularly based on material from what which is Now Morocco, um, and that date again may change, but certainly, around this period, we had organisms living in Africa that look a lot like us and, like their previous species, hobis, these humans also began to spread and migrate to different parts of the world Crossing the Middle East towards Europe and then towards Asia and when they did, of course, they realized that they had arrived at a place where there was already a human-like species, so In particular, in Europe there is clear evidence of anatomically modern Homo. sapiens entered Europe and essentially encountered the indigenous Nandal population that was there at the time.

We have less material from Asia, but it is reasonable to expect that we would have had similar interaction with Dennis Sen and possibly even with the Flores individuals in Indonesia, so anatomically modern humans have migrated out of Africa, have reached these places, have met all these other species about 50,000 years ago and completely by coincidence, each one of these other species then.goes extinct um that feels a bit like a story like that seems a bit of a coincidence isn't it that modern humans migrate out of Africa and one by one everyone who looks like us dies um and in particular I think if you think about In the recent history of humanity, we don't have a very good track record of interacting with people in their own countries.

When we get there, if you think about the first European settlers in virtually any other part of the world, that story didn't end well. for people who were already there, for a long time the rhetoric of modern human evolution really assumed that I think the extinction of these indigenous species was a direct result of conflict with modern humans, in other words, we appeared in Europe. I saw these Indians I thought they were a bit annoying and I killed them and took their place. There are two reasons why that is probably not true. The first is that so far we have no direct evidence of that, so, for example, there is no evidence from Neal. skeletons that have wounds inflicted by weapons, we don't have evidence of mass genocide, we don't have any of that that can support that argument and the second evidence, I'll tell you in a second, that suggests that we could have had a much more positive relationship at least with some of those uh some of those species um so we don't really know why all of those species went extinct there's no evidence that we deliberately eradicated them but there are certainly several suggestions of things that could have probably contributed in a combination to lead to these other species to extinction, the first is that this was a period of significant climate challenge, I guess for these species, uh, so I don't know how well this looks on this graph above, the blue graph here shows the global temperature average, um. going from a long time ago, 800,000 years ago, to today here and what you can see maybe up here in the top corner is a long period here, between about uh, 100 uh, 150,000 years ago and, more recently, of temperatures prolonged cold, um.

So this had two effects: one, the world was colder, second, it was also much drier because when the world is cold, a lot of water is locked up in layers of ice and everything becomes much drier, so one possibility is this very prolonged period of cold and dry weather. uh presented a significant challenge, particularly for those human-like species that lived in colder parts of the world, so the neighbor in Europe, for example, Dennis in Siberia, may have struggled to deal with that prolonged cold spell of a way that maybe uh anatomically modern humans didn't. There is also evidence at that time of several really large volcanic eruptions, particularly in areas such as what is now Italy and in the Polynesia area and areas of Indonesia, which probably produced a very large quantity. of smoke and ash essentially, um, which has direct impacts, obviously, it's not very pleasant to live in a place where you have ash falling on you and also indirect impacts in terms of climate change in the local region.

Most evidence now suggests this. alone is not enough to explain the Extinction, but it certainly probably wouldn't have helped humans living in those areas. A third possibility, um, and one that is close to my heart given that I spent most of my life working in infectious diseases, is that maybe this was some kind of horrendous pandemic for these particular species, maybe even one that It was precipitated by the arrival of modern humans and if you think about that, for example, when the Europeans came to the new world, they brought with them inadvertently at first deliberately afterwards, eh, little poox. a disease that was then endemic in Europe but was not endemic in the North was North America um and therefore the Native Americans had almost no resistance to smallpox um and this disease absolutely devastated the Native American population um and uh so and This is a This is a frequently occurring pattern, so one possibility is that when modern humans migrated out of Africa, they brought with them perhaps some pathogens that they were relatively resistant to after they had coevolved, but these indigenous populations , who had never seen them before, were very susceptible, so perhaps Emm, they inadvertently eradicated Neals and others by bringing their pathogens with them.

A fourth possibility, um, and one that's gotten a lot of traction in the press, I think is about tool use, uh, and until recently, this seemed pretty compelling. a very good set of data on anatomically modern humans, creating quite elaborate tools and using them to capture and kill animals, for example, and, indeed, to do things like make primitive clothing, and this was not something that had been seen with others fossil materials. So the suggestion was that maybe we were just technologically superior, we had these incredible tools and they allowed us, for example, to hunt mammoths and other things, we always had the food and we were starving because they couldn't compete, that has largely been excrement .

I screwed over more recent discoveries of tools that were clearly associated with the annals, and indeed the demonstration that the annals could produce equally elaborate tools and, in fact, had control of things like fire, so actually that Technological difference between modern humans and annals is nowhere to be found. It's almost as surprising as it seemed at first and probably again not enough to explain this, so the latest suggestion that people have made is that perhaps this is something about the elaborate intelligent cultural life that characterizes Homo sapiens. We know it's a key feature. of homo sapiens is his amazing brain capacity and his ability to think about things that are quite abstract and this is one of my favorite examples.

This sculpture called The Lion Man dates back to about 40,000 years ago and was found in Germany. It was produced by anatomically modern. humans we think um and it's a really good example. I think about the level of sophistication of these primitive humans in Inver commas because this is a really nice piece of art that has been created by someone who we consider very prehistoric. uh, but B also demonstrates his ability to think in abstract thoughts because this is something that doesn't exist, right, we don't have bipedal lions and as far as we know, we never have, so this is a demonstration of a fusion of ideas and We don't know why they did that.

It's been speculated that maybe it's some kind of religious meaning, or maybe something for some kind of cultural purpose, but either way, the idea that a modern human sitting in some cave would create something that was a fusion between a human and a lion for some kind of artistic purpose rather than as a practical tool suggests a level of sophistication that we haven't yet seen in other species um and that's why I said at the beginning of the lecture that I wasn't going to answer my question and I'm not, but we don't know the answer, but I guess the most plausible explanation for the extinction of these other species at this stage is some complex combination of a difficult climate and maybe a pathogen and technological and cultural superiority, um for whatever reason, About 38,000 years ago we were alone, all these other species had gone extinct and since then, as far as we know, Homo sapiens has been the only homo species on the planet, but to end on a slightly happier note, it's not quite like that. simple because in recent years we have learned that, although those other species are extinct, they have left a truly exciting remnant and we have learned this from the revolution of ancient DNA technologies, particularly promoted by Sant Parbo, a Swede. uh uh geneticist who has spent his life really optimizing the ability to recover and sequence DNA from very ancient material and for which he received the Nobel Prize in 2022 um and what Pao and others have done is extract DNA they managed to extract DNA from this ancient material And look, sequence it and in 2010, which was a dramatic year for this field, they came up with two really impressive findings.

The first was that they had successfully extracted and sequenced the DNA to create a genome, a complete genome sequence, of Aandal, which was nice. revolutionary at the time and even more revolutionary because actually as part of this project they had been sequencing different nandal materials and they realized that one of the pieces of material they said was not NE anill at all and was in fact this species I. I've been talking to you about Dennis ens and this remains the first and only example of us discovering a species of homo through DNA sequencing technology rather than through fossil identification.

Once that was done, people looked at the same material and realized that there were subtle differences, but either way this was the first discovery of a different species. We now have extensive genomic information for both species. Unfortunately we do not have it for that addition, the Flores skeleton, that is probably because the DNA is not preserved very well. In the tropics, there have been attempts, but without success, to recover DNA from that Indonesian sample, whereas these samples come from much colder climates where DNA is better preserved, but when we have these genome sequences from these two species together Of course, with the enormous amount of genomic information we have about modern Homo sapiens, we can now make some really interesting comparisons and what was most surprising as soon as this comparison was made was that it shed a huge amount of light on this early diversification. and expansion of our species in particular validated many of the dates that modern Homo sapiens had left and moved around Africa and the reason it did so was because of a pretty remarkable discovery, which is that when you compare those two sequences, those Neals and Denisovan genomic sequences with modern human genomes, you will find that many of us, human beings living today, but not all of us have fragments of those genomes within us, in fact, if so , if you're sitting in this room or listening online and you can trace your ancestry intact uh through Africa just Africa then you're 100% on average 100% Homo sapiens genome if you're like me if you're Eurasian um on average you're about 98% Homo sapiens but we most Asians carry about 2% of their genome that they inherited from Neals um and if you come from this part of the world here Polynesia if you are Melanesian um you have that 2% of the anital and also up to about 4% Denisovan and that means two really important things: firstly, it means that at one point in relatively recent evolutionary history modern Homo sapiens did indeed cohabit areas with these other two species because the second point is that we also interbred with them and in fact because we detected that at such high levels we probably intersected with them quite a bit actually um and you can actually see this quite beautiful pattern this is quite recent work just in the last few months actually um looking at the level of Denisovan ancestry in modern humans throughout the world and what you see is that it is colored from blue to red.

What you see is that if you are from Africa or Europe, you essentially have no Dennis Haven ancestry on average and you get more and more. and more as you go until it looks about 5% down in this part of the world and one of the things I quite like about this, actually for people whoare familiar with this part of the world, it's something called the Wallace line. So Alfred Russell Wallace, working at the same time as Darwin, discovered the fact that if you look in this part of the world, the plants and animals on one side of the line are quite different from those on the other side of the line and that Because over evolutionary time, sea level has risen and fallen, so there have been land bridges that have allowed animals and plants to migrate between these areas, but there is a very deep channel that runs here and which has never dried out, so there has been a barrier. natural barrier for a long time, so you have a different evolutionary history from here to here, but that has not affected this rise, this migration of humans, which suggests that humans successfully navigated that stretch of water between these islands, whether deliberately on boats or inadvertently, you know. being blown by the wind on rafts of vegetation or something, so this is a really good piece of information that suggests that modern humans are derived from some of these interbreeding with ancient species and, in fact, what we now believe is a model that It looks a little like this.

So, between 300 and 200,000 years ago, modern humans evolved in Africa, migrated, encountered those Neals, as I mentioned before, didn't eradicate them all other than a horrendous genocide, and actually had quite a few romantic interactions with them. Of course, we don't have any information about whether those were forced interactions, or consensual, or some combination of the two, but nevertheless, what we do have is very clear genetic information that they interbred and then those hybrids, for once , or rather, those. Neal's modern human hybrids migrated further and encountered this new population, this Denisen population, and they did the same thing again, introducing a new set of genes and migrating further down here, so we all have these slightly different ancestors and I think That's the most interesting thing about this.

The fact that we can see it today suggests that it's probably not a very rare event, but in reality perhaps modern humans live alongside these other species for a relatively long period of time and the final piece of the puzzle that suggests it is It's probably really true, this is the bone fragment that I showed you on some slides, one of the bone fragments from that cave in Denisova and I said there was very little, um, kind of fossil material, so the bone material from these individuals, well, this is one, this is a leg or an arm, we don't know which from Adis Soven and it turned out more recently, the same teams, the Fanta paro team, successfully obtained the DNA from this and sequenced the DNA from this.

When they did, it turns out that this individual was a first-generation hybrid, not between Homo sapiens but between Dennis Havens and Neals. father and a father from Dennis Haven, either we were incredibly lucky and found a first generation hybrid in a sample that is absolutely small or this suggests, and I would suggest that it is more likely that this was something very common, so you had Homo sapiens and Denisovans and Ne annals live close enough and reproduce that now, thousands of years later, a small bone fragment demonstrates a first generation, a mixed progeny, from one of these matings, suggesting perhaps that we have had this type of interaction many, many times until these other species became extinct and that suggests that actually our family tree, if you will, is much more complicated than we used to think, rather it was a simple and very nice branching and all the others died out and we are here in splendid isolation. they have these frequent respiration events between different lineages, some of which then go extinct but leave their genetic stamp on modern humans, and in fact, if you're interested, you'll go into great detail about all the different ancestors around the world and what parts of its genome could have come from different human lineages mentioned, it's a pretty fascinating dig and so instead of thinking of human evolution as this kind of biblical pinnacle of success with a single species at the top, we're actually much more like that.

Really complicated branching tree with a lot of crossing branches and maybe now, you know, right now we're alone as a species, but who knows, if we turn the clock forward 100 thousand years from now, we might have all kinds of interesting diversification yet to come. . And on that note, thank you very much for listening. I'm very happy. Answer any question, so the conclusion is quite surprising. Because it seems to me that there are a couple of bigger possibilities that can arise from this. So would you say maybe we need to start? rethink our idea of ​​what species means, can we be so discreet or isolationist about it?

Yeah, I think that's a very good point and I think so. I said at the beginning that this biological species concept is defined by organisms that reproduce. together and we can't breathe with anyone else and then I told them that we have this repeated in breathing between groups, so one argument would be to say that they're not really different species at all, and that we were all one big guy. from the Blended group and I think to some extent this is a kind of semantic argument and the example I always use is domestic dogs, dogs are one species, right, they are one species, however, in nature , if you distributed them in a large quantity.

A Dane and a Chihuahua are very unlikely to form a stable, long-lasting reproduction of species, um, for pretty obvious reasons, um, and if you want, you can play with that and say that these are nascent species that are about to branch out, um, and maybe this is What we're looking at here is a snapshot in time when these different human lineages were almost but not quite separate and then they were gone. What they haven't done is we obviously haven't fully introgressed like we did in Genesis. It hasn't merged again because we only know two or three or four percent of these other genomes, so it's not like we're not a mix of all these species, they're still very much a species of homo sapiens with a little about other things, but the fact that we crossed paths suggests that there was no species barrier, but it certainly wasn't black and white.

Hello, thank you for your conference. In the context of what you just told us, could you tell us something about what race means? I'd rather not do it like that, like that, like that, so the first thing that says that biologically race has no meaning doesn't mean anything at all um and it's a word obviously that has massive cultural connotations, many of them quite negative um, so I think that there are probably there are probably two things to say as identifying a type of cultural belonging. It means a lot to some people. People have very strong feelings one way or another.

Either you know that yes, I'm completely in this group or you don't. not like something that you can see biologically, it doesn't make much sense and in fact, genetically it's almost impossible, so if we look, you know, if I look around this room, for example, all over the world, people belong to what which historically people could have called genetically different races. You wouldn't see it, so there are many more differences within groups than between groups. There are certain traits associated with certain people from certain parts of the world, but not enough to say that you know this is one particular group and this is another. particular group, um, so biologically it doesn't make sense, the place where it's probably developed in the evolutionary sense is actually around that idea of ​​self-determination, so, for example, what sometimes happens in groups of organisms diversified is that they have patterns of reproduction inbreeding, it's called that when you reproduce with similar groups and you see that in humanity, so there are some groups, religious groups, cultural groups, wherever they encourage you to marry and reproduce within your group and not out of your group if you play that for thousands. of years that could end up in diversification because you have this genetic isolation, in reality, of course, what happened is precisely the opposite and now we all fly around the world and you know, ignore that completely, um, and then you have a one species of I, um, which defines if you like the role in terms of the way people interact with each other, but it's not a biologically significant thing at all, what kind of numbers of these species were on the planet, um, for play right now and where it is. that other one and yeah, and for how many years or so did these species coexist, right, in terms of numbers, all we can say with conf, so we only have that, for example, if I take uh floresiensis as the best example, we only have I found fanis on Flores in Indonesia and I think something like 100 individuals have been found, so they might have been common locally, but they certainly weren't common globally, or if they were, we haven't found them anywhere else , which seems a little unlikely that we Andals have a large amount of weaving material from all of Western Europe and some of Eastern Europe.

They were probably relatively abundant in that area, but in that area alone there is no Neal material from other parts of the world uh Dennis Havens we have very little information about them they have been found in a couple of places again very fragmentary material, although the fact that that there is a fairly large genetic presence in modern human populations might suggest that they were relatively abundant um, but I mean, to be perfectly honest, it's all a bit complicated in terms of how long we could have cohabited, I want better words, um, that's very controversial and a little confusing, um, so you can put limits on it.

So if you imagine that modern humans emerged from Africa and crossed over, say, 60 thousand years ago and that they all went extinct 38,000 years ago, it can't be more than about 30,000 years ago, it was probably much shorter, there is some evidence that there is . some caves where there is material that appears to have been produced by both hopan and the annals, um that extends over a reasonably long period of time, so there is a suggestion that we could have inhabited certain sites for possibly a couple of thousand of years, um, but I Yo, this is kind of open to negotiation.

I think it's possibly a reasonable period of time, but in terms of evolutionary time, a very brief snapshot. You mentioned that there is no distinction in the question of race, genetically or biologically. uh, hair, for example, does distinguish between races, right? uh no, it really doesn't, so I guess this gets a little bit to the point of whether there are traits that are more common in some populations than in other populations, um, for example, uh. You know that there are some populations in Africa where there are a disproportionately high number of people who can run very fast.

You can see that, you know, being represented in some kind of international sport, that doesn't mean that if you come from that part of Africa. In Africa you're going to be an Olympic gold medalist, so there are associations with certain traits, but there's nothing black and white, anything like that, that's associated with what people might call a race or a tribe or something like that. a good example is blonde hair, so for example if you look at blonde hair around the world, there's a lot of blonde hair in sort of Europe, not a lot of blonde hair in Africa, but there are still individual people who have blonde hair. and particularly in itself exactly. or curly hair or all these kinds of different things so there are no traits that can mark someone as something in particular there are things that are more common or less common and that's what you see genetically also is that you can um So if you, for example, have fossil material, you can make assumptions about the skin color of that individual, for example, but you cannot define it, you cannot do the opposite, you cannot say because this skin color is here that person must have been part of this group, does that apply the color?

Well, yes, it applies to almost everything, eye color, all kinds of things, so there are traits that are much more common in some areas than others, but essentially we are a large and interesting genetic mixing group that I think which is fabulous, one question is: have we lost most of the Neanderthals and Dennis? Dennis is right Den, yes, den genes because we were better adapted and they were not adaptive, to which I could add something like Is it actually a more positive spin? uh, Homo sapiens' ability for butt simulation is what really helped them the most.

Is it adaptive capacity? A similar capacity. Yes, that's a great question. So the short answer is that it goes both ways, e.g. there are some genes in the modern human population, so there is a gene that is an HLA gene, so this is a gene that helps your immune system essentially recognize something that is foreign and one of these comes in different flavors and one of The really fascinating thing is that there is a particular flavor of HLA Al, it's called, it's quite common in modern Homo sapiens and it seems to have relatively recent evolutionary ancestry and it turns out that's because it's actually a Denis Soven allele, so it seems an example in which we have interpreted that we havepicked up a gene that benefited us and therefore spread rapidly.

There are also examples the other way around, so there are particular genes that we can see in the immediate genome that are not represented. not at all suggesting that they were actually harmful, they were harmful in this type of process, so it could be, for example, something that led to some kind of incompatibility in reproduction, so there is something in other species that you see things like male sterility where they have particular genes that just don't work in a different host and therefore cause a loss of reproductive capacity, those kinds of things that we see, so essentially the short answer to that very long answer that I just give you is that there are genes that have been beneficial to us and genes that have not been and those have been lost through evolutionary processes and there is a fairly remote possibility.

I think I can imagine what the answer will be, but I'm going to ask it anyway, it's quite An interesting question was interbreeding between Homo sapiens Neanderthal Dennis Saen. Was it driven more by the males or females of the species? I'm not sure there is a sure answer to that question. Is there the short answer that we don't know? There are examples in both directions, as far as I know, where you can see them so you can trace in the genome whether that inheritance comes from a male or female lineage based on the genes that are there, and I'm trying to think.

Off the top of my head, I think there are examples in both directions. I don't think we have enough data to see if there's a preponderance one way or another, um, on that and the Denny fact, the f that I just showed you. in the end, which is this Nandal Dennis Oven um hybrid for a better word, we certainly don't have enough material like that to be able to really say that this was a particular um bias, uh, so yeah, I don't know what the program is. answer, well, well played, can you tell us what happened to Homo erectus?

Oh yeah, so Homoerectus, um, we most likely don't have hom anymore, but as far as we can tell, that's not due to a dramatic extinction, it's probably a species that does. essentially evolved and morphed into later species and has slowly been lost over time rather than being displaced and eliminated, so on the slide that I showed you earlier there are some lineages where we see sort of an abrupt end and they disappear, that's not true for homoerectus um and that is um thought of as a species that essentially just diversified into more modern humans um and so we are all to a first approximation just descendants of homoerectus does all of this help us understand ourselves as modern humans um does it help us ?

We better understand our type of psychology, our mental health, our cognitive development, and does it tell us if there is any possibility that we can continue to evolve and that, in fact, homosapiens can split into different types of humans in the future? The first one I like to think so and I think one of the things that I mean, one of the things I like most about this is that it demonstrates the complete stupidity of so many types of human ideas that have been so negative throughout history. recent human. The idea that you know someone asked about race before.

The idea that there is some kind of race. You know, the superior race and the inferior race are clearly complete nonsense, the idea that, you know, somehow we are all very different and need to maintain our own entities. We're actually being a huge genetic mix, you know, for thousands of years. um and I also think maybe the lesson that you know no matter how optimal you are, your time in the kind of sun will come and go. um you know there was a time when annals were the dominant species in Europe and we're not here anymore, we're here, we probably won't be here forever, so you know, make the most of it, so, yeah, I like to think that There's kind of a positive story here, there's also a very negative twist, you know? we roam the world and eradicate people and you know, maybe we had forced meetings and all kinds of negative things, but let's stick with the positive answer, um, in terms of future evolution, stay with the show, whoever asked that question in a conference with you. very soon I think not the next one or the next one we're going to talk a little bit about where we might go um spoiler alert yeah absolutely I mean evolution doesn't stop uh so I'm sure we'll evolve in all kinds of interesting ways but you'll have than stick around and see at least what I think about it, um and uh, it's open to being shot down in flames when everyone disagrees with it.

Sorry, I just wanted to ask you about your um homo hiyal. Burgus, who you think developed in Africa and then moved and diversified, so the Heidleberg jaw that was found is that they are older than Neander souls or they were still around at this time, yeah, so that's a very good question. so it's older, um uh, but it's a little bit unclear whether how it got there, where it came from or how common it was to have those species there. It's probably a high-end early beige that arrived before diversifying into these nearby populations later, um. In terms of Hide Against, we have good material in Africa now, so I think the oldest material is in Morocco, and then, yeah, I'm trying to remember my dates.

I think Ethiopia is a little bit younger and South Africa is younger again. so there's a suggestion that there was a sort of migratory evolution of Heidleberg Enis through Africa at the same time he left and crossed into Europe, um, but with all these things, the dating is you know there are a lot of people who become very I'm worried about appointments, um and uh, there's a lot of flexibility there and you know that as new technologies are developed and new material becomes available, dates change radically, so don't force me to make that my get-out clause, Professor.

Robin May. Thank you so much