Gresham College Lectures

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

January 15, 2024 Gresham College
Gresham College Lectures
Why Is There Only One Species of Human? - Robin May
Show Notes Transcript

We are the only human species on the planet today. But for most of our history we have not been alone.

Fossil and genetic evidence has revealed a diverse and fascinating set of human-like species, from Neanderthals to Denisovans, to Homo Floresiensis (The Hobbit) and more.

We’ll meet many of them in this lecture, investigate why they died out and reveal why some of them are much closer relatives than you might think.

This lecture was recorded by Robin May on 10th January 2024 at Barnard's Inn Hall, London.

The transcript and downloadable versions of the lecture are available from the Gresham College website:

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But what I wanna do tonight is think a little bit about how we got here, uh, and maybe speculate a bit about the factors that might have driven that evolution, uh, and perhaps even going forwards. Um, and there aren't other species with which we reproduce. But because we want to encourage a love of learning, we think it's well worth it. And in fact, these are, uh, a North American species, but closer to home. So there are lots and lots of examples of species that are very similar, living relatively close to each other. So in fact, uh, in this estimate from 2018, almost a quarter of the world's land surface is still classed as wilderness IE it has relatively little human habitation or human activity shown here. And by, uh, recent estimates, it's about two or 3%, um, of the world's land surface has genuinely not had humans access it. Maybe? And this, of course, was something that early, uh, explorers, European explorers in particular, um, floated as ideas. So this for example, is a picture of, uh, Charles Darwin arriving in South America on his voyage, on the Beagle. And in fact, uh, by genetic data, we know that we share something like 98% of our genome with chimpanzees that's pretty high. And so perhaps chimpanzees are actually a species, uh, to humanity. The distance is much higher. Often they were animals. Um, for example, like this skull dug out of a quarry in Gibraltar in the early 18 hundreds when they'd done that, these were typically described by the scientific community, at least as archaic humans. So they were humans that had been around, uh, for a long time. So people say, oh, they're extinct giants. Um, or they were kind of mythological 12 headed beasts or something. Um, however, in 1891, this rather dashing cap here with the, uh, with the nice mustache, Eugene Dubois, who was a Dutch anatomist, was working in what was then the Dutch East Indies, now Indonesia. He started to collect some of these and classify them together, and, uh, realized that one collection of, uh, skeletal material, um, belonged to something that looked very human-like. So within the genus homo. So now as we start to turn into the, uh, the end of the 18 hundreds, um, we have a position where there are at least two species of homos and Alis, um, and, uh, what is now home erectus that, uh, we think have existed and no longer do exist. So the world is starting to view, uh, the fact that we are perhaps haven't always been alone, uh, through quite a different, uh, lens. And he, uh, was a German industrialist. This is what we now know of as Homo Heidelbergensis named by him. Um, and this is an incredibly fast moving, uh, field. Um, uh, so to avoid you all putting the blame on me, I've lifted this rather nice diagram from the History Museum, so you can blame them for it being outta date. Instead, um, we, we now know, um, that there are many, many species of now extinct homo, that have existed and have existed in parallel. So, for example, um, here in this top corner, you can see at least four or five species that have been present on the planet at the same time, um, for a large period of our history, but are no longer present with us today. What has happened to drive this colonization of homo sapiens around the world and to remove these other species? But as we know at the moment, there are at least four parallel species of homo like organisms, so like ourselves that have coexisted in relatively recent evolutionary history. Um, if it's running down your face and dripping off your chin, then you're probably a homosapiens. And if, if not, please come to see me afterwards.'cause it really ruins the lecture if you're a Neal. Um, so these, so we know a lot about the Neals. Um, because as you can see from this, it's very small. So sim they were not very small, for example, like the Flores, um, species. So they were, they were present at the same time. The view is that, uh, around 600,000 years ago, Hodel bagis, you'll remember, that's the jawbone that was reported, uh, from Germany, um, was a sort of most recent common ancestor of modern humans evolving in Africa about 600,000 years ago. Once located in those parts of the world like species do, and like those of you who are earlier lectures, will we recall, um, it started to diversify and it started to, in the normal process of evolution, accumulate mutations, accumulate phenotypic change. We had a similar interaction with de sapiens and possibly even, um, down with the Flores individuals in Indonesia. If you think about early European settlers in pretty much any other part of the globe, that story did not end well for the people who were already there. Um, so we don't actually know why those species all became extinct. The first is that this was a period of significant climate challenge, I guess, for these species. Uh, so I dunno how well this comes across. Um, and one which has had a lot of traction in the press, I think is about the use of tools. Um, and this was not something that was seen with other fossil materials. Uh, but b, it also demonstrates their ability to think in abstract thoughts because this is something that does not exist, right? Um, so this is a demonstration of a fusion of ideas, and we don't know why they made that. Um, and so I said at the beginning of the lecture, I wasn't gonna answer my question, and I'm not, 'cause we don't know the answer, but the, 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 a technological and cultural superiority. The first was they had successfully extracted and sequence DNA to create a genome, a full genome sequence, uh, from a Neanderthal, which was pre-revolutionary at the time. And then even more revolutionary from that, they had actually, as part of this project been sequencing different Neanderthal material and realized that one of the pieces of material they were sent was not Neanderthal at all. Um, and so there's been, there's been attempts but no success in retrieving DNA from that, uh, sample from Indonesia. In particular, it validated many of the dates at which, uh, homo sapiens, modern homo sapiens had left and moved around Africa. This is, um, some work fairly recently, just in the last couple of months actually, um, looking at a level of Denis Saban ancestry in modern humans across the world. So this is a really nice piece of data suggesting that modern humans derive from some of these crosses with ancient species. And I said there was very little, um, uh, sort of fossil materials, a bone material from these individuals. Well, this is one, this is either a leg or an arm, we dunno, which, um, from a Denis. And so rather than thinking of human evolution as this kind of, um, biblical pinnacle of success with a single species at the top, we're in fact much more like this really complicated branching tree with lots of cross branches. And perhaps now, uh, we know for this moment in time we are on our own as this species. I'm very happy to take any questions. Yeah, I think that's a really good point. And I, I, I think so this, I said at the beginning that this biological species concept is defined by organisms that breed together and can't breed with anybody else. Uh, and I think to a certain extent this is a sort of semantic argument. And, and the example I always use is dog, domestic dogs are a single species, right? However, out there in the wild, if you've distributed them, a great Dane and a chihuahua are very unlikely to form stable, long-lasting species reproduction, um, for quite obvious reasons. Um, and maybe this is what we're seeing here is a, a snapshot in time when these different human lineages were kind of almost separate but not quite, um, and then have gone. There's still very much a homo sapien species with a little bit of other things in, but the fact we have interbred does suggest that the species barrier was not, was certainly not black and white. Hi, thank you for your lecture. It, it means a lot to some people. So if we look, you know, if I look around this room, for example, around the world, um, people belong to what historically people might have called different races. So there's some groups, religious groups, cultural groups, whatever, where you are encouraged to marry and reproduce within your group and not outside your group. Uh, right, so in terms of numbers, so, uh, all we can say with con, so we've only, so for example, if I take, uh, Florensis as the best example, we have only found florensis in Flores, in Indonesia. We have a huge amount of tissue, uh, material from right across, uh, sort of western Europe and into parts of Eastern Europe. You can see that, uh, you know, in, in represented in kind of international sports. Um, uh, and so there are associations with certain traits, but there is no black and white, um, sort of thing that is associated with what, with what people might term a race or a tribe or something like that. Say for example, you know, if you look around the world, blonde hair's, lots of blonde hair in sort of Europe, not very much blonde hair in Africa, but there are still individual people who have blonde hair and particularly yes, exactly, or curly hair or all these kind of different things. Applies to pretty much everything, eye color, all sorts of things. Aven? So, um, is it sort of adaptive capacity, assimilator capacity? Uh, there are also examples the other way around. And there's, this is probably a long shot. I, I, I think I can imagine what the answer's gonna be, but I'm gonna ask it anyway 'cause it's quite an interesting one. Uh, was the interbreeding between homo sapiens Neanderthal, uh, Dennis Saban, was it, was it driven more by the males or the females of the species? I'm not sure there's a safe answer to that question. Is there, um, the short answer is we don't know. So there are examples in both directions as far as I'm aware, where you can see. So you can track in the genome whether that inheritance has come from a male or female lineage based on the genes that are there. Um, and I, I'm just 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 whether there is a preponderance of one way, uh, or the other, um, in that period. And the fact that Denny, the fossil I just showed you at the end, which is this neanderthal denisov, um, hybrid for want of a better word, we certainly don't have enough material like that to be able to really say this was a particular, um, bias. Uh, so yeah. So don't know is the short answer. Okay. Okay. Well played. Well played. Can you tell us what happened to Homoerectus? Can you tell us what happened to Homoerectus? Ah, yes. Ah, yes. So, so Homoerectus, um, it, so probably, so we don't have homoerectus anymore, but as far as we can tell that's not due to a dramatic extinction. So, so Homoerectus, um, it, so probably, so we don't have homoerectus anymore, but as far as we can tell that's not due to a dramatic extinction. It's probably a species that has essentially evolved and morphed into later species and has slowly been lost over time, rather than being displaced and eliminated. It's probably a species that has essentially evolved and morphed into later species and has slowly been lost over time, rather than being displaced and eliminated. So there are, back on the slide I showed you previously, there are some lineages where we see a sort of abrupt end and they disappear. That's not true for home erectus. Um, and so 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 home erectus. Does all this help us understand our, uh, ourselves as modern humans? Um, help us understand our kind of psychology, our mental health, our cognitive development better? And does it, does it tell us is there any possibility that we might continue to evolve and that indeed home sapiens might split into to future, to different sorts of humans in the future? Great. So on the first one, I like to think it does, and I think one of the things, I mean, one of the things I I most like about this is it demonstrates the complete stupidity of so many sort of human ideas that have been so negative over recent human history, right? The idea that, you know, someone asked about race earlier, the idea that there's some kind of, you know, superior race and inferior race is complete, clearly complete nonsense. Um, the idea that, uh, you know, we are somehow all very distinct and need to keep to our own entities. We're actually being a massive genetic mixing pot, uh, you know, for thousands of years. Um, and, and also I think perhaps the lesson that, you know, it doesn't matter how optimal you are, your time in the kind of sun will come and go. Um, you know, there was a time when Neals with the dominant species in Europe and they're not around anymore. Um, we are around, we probably are not gonna be around forever. So, you know, make the most of it. Um, so, so yes, I like to think there's a kind of positive, uh, story here. There's also a very negative spin, you know, we kind of roamed the world and eradicated people and, you know, maybe had forced meetings, all sorts of negative things, but let's stick to the positive, uh, answer. Um, in terms of future evolution, stick with the program, whoever asked that question coming up in a lecture to you very soon, I think not the next one or the one after that, we're gonna talk a bit about. We, we might, might go, um, spoiler alert. Yes, absolutely. I, I mean, evolution doesn't stop. Uh, so I'm sure we'll be evolving all sorts of interesting ways, but you'll have to stick around and see at least what I think about that. Um, and uh, it's open to be shot down in flames when everyone disagrees with it. Fantastic. Um, sorry, I just wanted to ask about your, um, homeowner title burgs, who you, you think developed in Africa and then moved out and diversified. So the, the Heidelberg jaw that was found, is that, is that an a, is it older than the NDAs or were they still around at this time of, Yes, so that's a very good question. So it is 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 is probably an early heidelbergensis that arrived before diversifying into these Neal populations later on. Um, in terms of Heidelbergensis in Africa, we now have good material from, so the oldest material I think is up in uh, Morocco. Um, and then, yeah, I'm trying to remember my dates. I think then Ethiopia is a bit younger and South Africa younger again. So there's a suggestion. There was a sort of migration evolution of Heidelberg down through Africa at the same time as it went out and across into Europe. Um, but with all of these things, the dating is, you know, there's a lot of people, people get very worked up about dating, um, and uh, there's a lot of, uh, you know, flexibility there. And you know, as new technologies develop and new material becomes available, the dates change quite radically. So don't hold me to, that is my get out clause. Profess Robin may. Thank you very much. Thank you.