In Our Time - Human Evolution

Episode Date: February 16, 2006

Melvyn Bragg and guests discuss the story of human evolution, which stretches back over six million years. It is not the story of one species but of several diverse species, some of whom walked the Earth at the same time. From the earliest hominids to the early Homo sapiens, there was nothing inevitable about the course of human evolution. But what conditions created the opportunity for diverse human species to thrive? What environmental factors led to the survival of one human species, but contributed to the extinction of so many others? What can the fossil record and the science of genetics tell us about our ancestors? How does the brain make modern man so unique in the natural world? With Steve Jones, Professor of Genetics in the Galton Laboratory at University College London; Fred Spoor, Professor of Evolutionary Anatomy at University College London; Margaret Clegg, Honorary Research Fellow in the Department of Biological Anthropology at University College London.

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or wherever you get your pods. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash radio 4. I hope you enjoy the program. Hello, the story of human evolution stretches back over about 6 million years. It's not the story of one species, but of several diverse species, some of whom walk the earth at the same time.

From the earliest hominids to the early Homo sapiens, there seems to be nothing inevitable about the cause. of human evolution. But what conditions created the opportunity for diverse human species to thrive? What environmental factors led to the survival of just one human species, but contributed to the extinction of so many others?

What can the fossil record and the science of genetics tell us about our ancestors? And how does the brain make modern man so unique in the natural world? With me to discuss human evolution is Steve Jones, Professor of Genetics in the Galton Laboratory at UCL, University of College London, Fred Spur, Professor of Evolutionary Anatomy at UCL, and Margaret Clegg,

Honorary Research Fellow in the Department of Biological Anthropology at UCL. Steve Jones, can we go as what we might call the beginning when we see the hominids come in? Well, we can, in a metaphorical sense. You can do it directly with fossils, and of course the fossil record by definition is very incomplete, but there's another way of looking at fossils because we're all fossils, we're all living fossils of our ancestors,

All chimpanzees are living fossils of their ancestors, and in fact we can draw a family tree in the genes, which links us to our joint ancestor. And if you make the rather daring assumption that the DNA changes at a regular rate and compare ourselves and chimps to, let's say, mice, which we know the original date of split reasonably well, you get up with this famous date of a split of around 6 million years ago

when the lineage that gave rise to us split from the lineage that gave rise to chimpanzee. Are we any idea how that happened or why it happened? I think the short answer is probably no, not in any detail, not without speculating. And that's true, of course, of most species. Darwin himself called the nature and the origin of species, the mystery of mysteries. His book is called the origin of species, but it's not very much about how species originate. So quite what drove the difference, we don't know.

Quite a common alibi, which is often important, is sex, which is an alibi for many things. and if you look at many of the differences between modern humans and modern chimpanzees, they're sexually driven. One of the most rapidly evolving sets of genetic differences between us and chimps is actually within the scrotum rather than within the skull

because all kinds of genes involved, for example, in making sperm proteins and very distinct in us and chimps. So maybe it had to do with who fancies whom at the very beginning, but we're not sure, I'll leave that to the paleontologists. And given that there was, let's say, for the sake of this program, that there was a split about six million years ago.

It might be five and a half a million years ago. What happened then? How did the thing get going? Well, I think what's striking about human evolution in particular is that it's really been pretty fast. I mean, to an evolutionist, six million years, isn't really a very long time at all. But in that period, there have been the fossils tell us,

great numbers of human-like species and direct and indirect ancestors of ourselves. only one of which has survived. And if you look at the DNA, famously, as most people know, we share 98.8% of our DNA with modern chimps, which is usually sold as being, isn't that amazing? We share so much DNA with chimps.

But actually, a 1% difference is quite a lot. You can do a huge lot of damage with one gene. So there are many hundreds of different genes that separate us from chimps, many of which, as I'm sure we'll come back to later, are involved in what we think of, specifically human things, like language and consciousness and so on.

How do you do dating and genetic, you're as a molecular biologist, how do you do dating over this period? Well, you do dating with your fingers crossed, like many kinds of dating. And there are numbers of assumptions in this process. They're not all bad. For example, you can see evolution happening,

let's say, with the AIDS virus in front of your very eyes. And you can see that the AIDS virus has changed in the last 30 or 40 years since it first appeared in the developed world. And it's changed at a regular rate, which fits actually one's assumption of the rate of change of the molecular clock.

What you do is take a pair of species, humans and chimps say, we don't or didn't have a particularly good fossil record, and then compare them in the larger context with other mammals, which have a much better one, and compare ourselves to cats and dogs and mice where we know from the fossils where the splits were, and we can take that with the rocks, look at the genetic differences,

and then ask how fast. does the molecular clock tick? So the molecular clock is a time when one species splits off from another? Well, the molecular clock is exactly what it says. It's the thing at which the DNA alters at an approximately regular rate. And by looking at the clock in ourselves

and the clock in chimps, we can ask when did they start to separate. So it's a timing mechanism which is filled with assumptions, I have to say. The one timing mechanism which is not filled with assumptions but has weaknesses of its own because it's incomplete, is the fossil record, because that's now very accurately timed by physics. And as we know, physics cannot lie, whereas biology does it all the time.

Fred, Fispo, let's come to this fossil record. When and where did the first hominids appear, and what did they look like from the fossil record? It depends a little bit what you would call a hominid or a hominin, as some people call them nowadays. There are now actually, over the last few years, a couple of fossils from Chad and from Kenya that are

around that 6 million mark and so that's very close or even slightly beyond the data geneticists have told us where the split would be from chimpanzees so one of the discussion with these fossils is are they actually from before the split and if they are from beyond the split are they on our line

or are they on the chimpanzee line then really good evidence after that and then it also becomes much better evidence much more complete really starts around the 4 million mark. There's a few data points, a few clusters of fossils around

5 million and bits and pieces, but the really good evidence starts about around 4 million. That's the Australopithecus. That's Australopithecus. And initially an ancestral, relatively primitive species

that then very quickly seem to evolve into Australopithecus aphorensis, which is the species that Lucy, the famous skeleton Lucy belongs to. So this is about 4 million, 3 and a half million years ago. Can you tell us just in a bit of detail? So there you are, getting fossils, you get them, and you say

this is 3 and 1⁄2 million years ago and this is Lucy. What do you find and how do you date it? What goes on? Well, you find in the case of Lucy, it's a partial skeleton which is extremely unusual. So you actually have bits of the limb bones, you have bits of the skull,

parts of all the bits of the body. Usually you just find, if you're lucky, you find an entire lower jaw or you find part of the skull. And in some cases you find a fragmentary skull. Nevertheless, there's a huge amount of information in there. But the first thing you have to do is indeed call in the geologists to see in what layer did you find it. And in East Africa, where we find most of these fossils, we're very lucky that has been a lot of volcanic activity. So these fossils are almost always sandwiched in between layers of volcanic tufts that can be dated very, accurately. So you get the geologists in

and then they take them back to the laboratories and they can date them very accurately. Yes, yes. But what else can you get out of these bones Fred? Because you can get a lot out, can't you? Can you just go on a bit and tell us a bit more what the fossils yield? Because people think fossils these lumps are rather interestingly interesting bits of bones and stuff.

But you can get, I want to know what you can get out. The crucial bits, I think the three themes that we look for on the hole is A, you can look at if you find a part of the skull, you can say something about the size of the brain, because humans are obviously quite unique by having this big brain. You can look at the teeth, and the teeth on the whole among mammals will tell you something about diet, what did they actually eat.

There are also chemical ways of looking at that, isotopes. We may talk about it a little bit later, maybe. And then the last very important aspect at the beginning of human evolution is the question, bipedal, being upright, yes or no? And if you find limb bones, they really leave their signal very well whether a creature walked upright or was still on four legs or was climbing in trees or whatever. So those three things you can actually read on the basis of the biology.

And so Lucy is getting near Homo sapiens? I wouldn't say so. That very first group until the emergence of, well, I would say the emergence of a species we call Homo erectus by two million years ago. almost everything before has a body plan that in many respects looks more ape-like but they were definitely upright

so they were upright but above the neck the head in many respects in Asthropithecus at least it looks rather chimp-like the brain is not much larger than that of a chimp and the only difference and that's interesting with what Steve said about the importance of sex

one of the hallmarks of human evolution of the early hominids is not only being upright but also having very small canines and canines that are usually impriments are about display and are about sexual differences and reduction of canine size and reduction of the difference between males and females is typically something that you find in even the very early ones.

Margaret Clegg, we know there are variety of homo species in existence at the same time. Why do you think there was, can you give some idea of this diversity? it's almost like, as it were, different tribes, different species wandering around, but not bumping into each other or not bumping into each other, interbreeding, interrelating. Can you just give us a picture of what was going on, say, about two million years ago, but homie erectus and who else is around?

It's really quite a difficult thing to tease out, to decide why there were all these different species. It's almost impossible to actually know. But we can surmise that they may have been filling different niches within the environment. So they're eating different sorts of diet. they're using the environment in a different way. Are they like different breeds of cattle?

Perhaps more like different species of other primates. Right. So that within, say, the baboons, we've got a variety of different species of baboons who have slightly different diets, live in slightly different environments. So it's almost... One could assume that the earlier hominids

would have lived in that sort of way. Now, as to whether they would have interacted or not, if they were in exactly the same environment at the same time, it's quite possible that they would have interacted at the sort of level that chimpanzees and baboons interact, where there might be a little bit of aggression over water resources or the young of one species might tease the young of the other species. But as to whether they would breed,

that would depend on whether they would recognise the sort of signals that you would send out to say, I'm a breeding partner. I'm around, I'm available. If they don't recognise that, and that's one of the things that often is the main reason why the species don't breed with one another, there are signals which are perhaps calls

or differences in the colouration of the coat, even if they look very similar, are enough to sort of divide them up and have them not breed with one another. Can we move on to Homo erectus, which is supposed to have come, coming about 1.8 million years ago and still been around a mere 50,000 years ago,

which is a twigger. And they began to move, and they moved out of Africa. First of all, why is Africa so important in all this? And secondly, where did they move to? Well, I think Africa is important through really a sort of set of circumstances. And a particular set of circumstances arose which made a sort of radiation of hominid species.

perhaps through drawing changes within the environment itself. As to why they left Africa, they are the first species that we have evidence of outside Africa. As to why they left, there could be several possible reasons. One could be a sort of population expansion so that you get too many individuals within a particular environment and small groups will start to move off and move further away.

to set up their own ranges, or they could be following the herds, they could have different migration patterns, or it could be climatic change, the environment changes, and they move further out. And you would only have to move a short distance every year to move a long way in a thousand years. What limitations do fossils have, Steve Jones, in telling us this story? I think the short answer is there aren't many of them,

is the main limitation. a lot more than they used to be, many, many more than they used to be, almost unbelievably many more than there were 20 or 30 years ago. But it's always very inferential, and I've read papers that try to work out what the political views of Homer Reckis was from the shape of his thigh. And it's terribly, terribly easy to over-interpret the fossil record.

I'm sure that nobody at UCL would dream of doing such a thing, but there are other places where there are learned discussions about basically nothing. I think you have to be very careful not to over-interpret. Having said that, the fossil record is the direct proof of the truth of evolution more than anything else. If you look at the origin of species, about one page in six deals with the fossil record. If you look at modern and evolutionary textbooks, probably one page in 30 does. They're all about genetics.

I think that's a mistake. The fossil record is the framework upon which everything else is built, and that's as or more true in human evolution than anything else. Fred, do you want to come in... Yes, I mean there is a tendency to think that oh well there's so few fossils but as Steve says

because there's so much effort has gone into finding them the fossil record of human evolution in general is actually extremely good if we compare it with lots of other mammal groups where paleontologists on the whole tend to look at much broader lines of what's going on and we tend to really focus by now

on rather small details and where the confusion obviously arises is when you have a very good fossil record and you can start to find little side branches that came to nothing, as Steve pointed out. So the whole, if you have four fossils in a deep past, it's very easy to make an evolutionary tree. You'll just line them up and connect a line. When you have a very good fossil record, it becomes much more complicated. Why do they die out? For home erectus?

Well, it's hard to know. Of course, 99.9% of all species have died out. And what frequently happens is that another form will evolve for one reason or another. And by definition, it's closely related to what went before and is driven to extinction. We can see that happening now with the chimpanzee. Now, it's a tragedy in some ways that the chimpanzee is dying out, but it is definitely dying out, and it's dying out because of us.

And I think that many of these earlier relatives of ours probably died out for approximately the same reason. Because of the next lot. Because of the next lot. But they've moved around Humorectus. They're found in parts of Europe. They're found in China. So they moved out.

But then they haven't quite died out in the sense that it was easy to say died out. They've lingered on. But the Neanderthals have come in. Can we just talk about those briefly before we hit Homer 7? Because they are fascinating. They were in many ways a talented group. I often think of them the Neanderthals as being the last true conservatives because they had a bunch of tools, don't tools.

which didn't change for tens or hundreds of thousands of years. Then came this snippy group Homo sapiens, and you can see this amazing shift in the tools. It must have been a bit like the Spaniards arriving in South America. Suddenly the South Americans and Native South Americans were faced with this astonishing technology, with horses, with guns. They had no idea what it was. They had no chance of survival, really.

And I think that was the situation with the Neanderthar. Neanderthals, if we come, I'd like to keep a few dates going around the place, Margarie. It's about, we have to say about it. every time I'm awfully sorry about that people who are listening. About a quarter of a million years ago to about 30,000 years ago. That's roughly the sort of time span. Given that there's been life here for 4 billion years, we were really out talking about a tiny, tiny

speck of time and that puts it in some sort of... So about quarter million years or 30,000 years ago. So the Neanderthals are there, now you think that they have been underestimated. We've underestimated the level of their... Their brains were bigger than ours for a start, well, yes. I mean... I'm homosexuals, I'm not...

You've got to think about it always in terms of body size. So they were a bit more robust than us. So really they've got brains about the same size as ours. If you look at it in gross terms, yes, their brains are bigger. But I think that one of the ways that we've underestimated them is that we've looked at them expecting to see something like a modern human. And they're also a successful species.

They cope to the very difficult environment, living in the ice age and able to survive. and survive very well during that time period. And one of the things is that because we don't find large amounts of art with them, we assume that they're not good. But actually, most of us don't produce art. It's just particular individuals within our society that do. And so we look at them through our best focus rather than through a more general focus.

And I think it's that aspect that's really important, that we need to sort of take our blinkers off when we look at the earlier species. Well, we haven't discovered more about what could be called their social life. We've got evidence of the first burials. One of the reasons that we find so many Neanderthals is that they were deliberately buried. And it's much easier to find them,

and certainly to find whole skeletons. That's a huge show, because just being dropping dead is the fate of... Yeah, and eaten by other animals. So they're starting to bury. Fred's waving his hand, right, Fred. Well, because there's, as far as I know, really convincing evidence for symbolic goods going with that burial is not available for neonatal. And so you can be cynical and say, well, you know, getting rid of smelly bodies is also a reason to bury. You're not in full of agreement.

So it's not necessarily. You go that you're going to subdued shriek and leave back in our chat. It's not necessarily an afterlife idea or something. I wasn't actually suggesting that there was anything more than the fact that they were actually deliberately doing something with the dead. Now, that doesn't necessarily imply that they had any sort of belief of afterlife. But we do find occasionally artifacts within. Now, they could be accidentally in there, but they could be deliberate. I've got to turn to Homo sapiens, otherwise, like creation itself, we might not.

not get that. Now, they're just very late. We've been talking about millions of years. We're talking about something like 120,000 years ago. A bit more. 150,000. Well, both, and for a change, the genetic evidence and the fossil evidence really coincides. Now, the oldest fossil evidence for things that really look like us, headwise, skull-wise,

is indeed nearly 200,000 years, which is a date that the geneticist have been floating around. I've got a $120,000 on my list here. That's absolutely fun. That's very... Underday, but we have very... Very good evidence now from Kenya and Ethiopia. They came out of Africa too, Homo sapiens. That's right.

So, as it were, coming out of... They come out of the same sort of nowhere that Homo erectus did in the undertama. We don't quite know how they got set off on that... No, that's rather different. Homo erectus, we indeed hardly know exactly where they came from, But the transition from Homo erectus to Homo sapiens in Africa is actually, it's not the greatest fossil record, but it is, you see nice transitional forms over a period between, let's say, 900,000 to the 200,000 when we see first modern humans. So we see first modern humans, and how do you recognize, Fred, briefly and succinctly that they are modern humans?

You're digging away, you get this and you say, ah, this is us, this is the beginning of our story, 200,000 years ago. Yes, you find a creature with a large brain, a small dentition, a face that is not very protruding, like even the Anatole's head. Small brow ridges, those are really the typical things that mark more than humans. Let's talk about the brain, Steve Jones. Why have they got this bigger brain? Five times bigger than one would expect from such a size. Body size compared with the primates, yes. So how did it get to me that big? Well, again, there's not a speculative.

There are many arguments as why did we suddenly get a bigger brains? I mean, it's not easy to say. A very popular one is that the usual alibi, which is sexual selection, which is that individuals with large brains got more mates, I must say, I've never noticed it myself. One lives in hope.

But it's indubitably the case that our brains are relatively large compared with other primates with chimpanzees. The interesting thing, though, as we've touched on already, compared with our immediate ancestors, really is not very much larger with Neanderthals. They're Neanderthals weren't our ancestors,

but our close relatives. So maybe it wasn't, you know, size really didn't matter that much. It's something else that changed, something perhaps more specific. There's a very recent paper about the genetics of the brain, which finds that there is a rare

genetic disease, microcephaly, which leads to children being born with very tiny and severely damaged brains. If you look at the DNA around this particular gene, at the normal version of it, it turns out that that segment of DNA is the same in, more or less the same in everybody, suggesting that there was a mutation that went,

a single mutation, that went for large brains, and was so advantageous that it spread very, very quickly, dragging all its neighbouring DNA with it. Why it was, we don't know, but it in indubitably it does seem to have happened. I think what it tells us, really, in the early modern humans, is there something totally new has happened. There's a new kind of genetics, which isn't in the DNA.

It's in the mind. and that's what makes us unique. I mean, the famous Gilbert Sullivan phrase is, Darwinian man, though well behaved, is nothing but a monkey shaved. Well, in the very boring sense, that's true. We are all shaved monkeys, looking around the table, some of us more shaved, but we are shaved monkeys. But that's only in the boring physical sense.

When you begin to look at the cultural side of things, then obviously we're entirely different, not just from every other primate, from every other animal. And that really makes us, unique, it's not in the DNA, it's in the brain. And I think that's when really modern humans begin is with this new kind of information transfer

which is not just down the generations but from person to person. So this brings us to language Margaret Clegg, which has become more of a... When did language sound has been there for a long time? Allulation and language probably started as musical language and so on and so forth. But then it becomes language.

Have we any idea when language became the sort of language that we would understand to be language? And what difference that made? Short answer is no, we don't. We have really no idea. But all modern humans have language. So we're going to have to have the capacity to have language

with the last common ancestor of all living humans. So that's going to be 200,000, 400,000 years ago. So you mean, in other words, we were technically set up to have language? The developments in the throat and that sort, and the tongue and that sort of thing? Well, that's a different, that's a different aspect. How are we going to come at it? Because language is very important.

We've got to come at it one way or the other. So let's have a go. When did language come out? And when do we know that it began to be? Have you no idea? It's very difficult. It's one of those really, really difficult. People have got all sorts of ideas.

Some people suggest a very late evolution of language, although that's really... Late being sort of 40,000, yes. But that's sort of beginning to really go out of the window. because because all humans have it, it's going to have to be quite early. Other than that, it wouldn't be in every... Except the distinguishing about homo sapiens is how fast things evolve. So you don't necessarily have to have the long run up to the crease that other things have.

It's not necessarily that it's the long run up. It's the fact that if we've spread out all across the world, we're going to need to have the capability, not necessarily have the language, but the capability to do it. when we're all in one place. Can we tug away at this language thing, isn't? There's some interesting biology behind it. It's probably been slightly over-interpreted.

There are particular genes, very rare, which when they mutate in humans, remove specifically the ability for language. There's one famous one called Fox P2. Now, let's remind ourselves that that's a gene that does many things. It was first found in fruit flies. There's a fruit-fly mutation. It's found in most living creatures.

But a very few babies are born who cannot deal with language, and they have a mutation in this gene. If you compare this gene in ourselves, compared to chimpanzees, we are unique in having two changes, amino acid, building block changes in that gene. So it could be the language gene. Well, maybe. Except that, some very bizarre things very recently,

it turns out that birds that can learn language, parrots, have got a very active version of this gene, whereas birds that can't learn language don't have an active version of this gene. If you take mice and you destroy this gene, you knock it out, they can't squeak. We're now in the middle of engineering mice to have the human version of this Fox B2 gene. Whether they can speak about it, I will tell you in a few months. Mark, do you want to come back on the language scene? I think language is one of our defining features.

It could have arisen to sort of enhance your social life to make it easier to deal with the larger group sizes of modern humans. It's probably the success why we manage to, I don't want to say, conquer the world that sounds so anthropomorphic in the sense. But it's destroy the world, whatever. Yeah, so whether that language and everything that comes with it is a good biological adaptation is something else, because we may well destroy ourselves very quickly with it. I think having a big brain might be an evolutionary disadvantage. Absolutely. It's very likely. It's very expensive.

I mean, there's strong evidence of, you know, we see it around this table, survival of the glibist. Oh, cruel cut. Just as well this programme's coming to an end and I can take you for a cup of tea and that will show you Okay, thank you very much Thanks, Steve Jones, Fredsport and Margaret Clegg And next week's programme will be about Catherine the Great The Enlightened Despot of 18th Century Russia

Thank you very much for listening We hope you've enjoyed this Radio 4 podcast You can find hundreds of other programmes About history, science and philosophy at BBC.com.com.com.com.com. Thank you.