In Our Time - Human Origins

Episode Date: April 27, 2000

Melvyn Bragg and guests discuss the evolution of the human species. Where did we come from - we being Homo Sapiens? Let’s not go back to the Big Bang or in search of Genesis, but sift through the evidence from biology, palaeontology, climatology and anthropology.The story of human evolution is one that stretches back over five million years, and during that time there are reckoned to have been between fifteen and twenty species of hominid to have walked this planet. From the earliest (Genus) Australopithecus (Species) Anamensis through times when there have been several divergent pre-human species existing at once, we have now arrived at a period unique in the history of the earth when a sole human species, Homo Sapiens, is in evidence right across the globe.With Leslie Aiello, Professor of Biological Anthropology, University College, London; Robert Foley, evolutionary ecologist, writer and lecturer in biological anthropology at Cambridge University; Mark Roberts, Field Archaeologist, Project Leader of Boxgrove excavation and the discoverer of ‘Boxgrove Man’.

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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 is one that stretches back over about 5 million years. And during that time, there are reckoned have been between 15 and 20 species of hominid and they've walked this planet.

We've now arrived at a period unique in the history of the Earth when a sole human species, homo sapiens, is in evidence right across the globe. With me to give it insight into how we've arrived at this state of affairs over five million years and to explain some of the extraordinary detective work necessary to get any idea of the story of human origins is the paleoanthropologist Professor Leslie Islow from University College London, the paleoecologist Robert Foley from Cambridge University, and the field archaeologist and discoverer of Boxgrove man, Mark Roberts. Robert Foley, humans are held, so you say, to have evolved from,

apes, not monkeys. What was it about apes that spurred them to evolve in such a way as we came from them? Well, apes are a really rather specialized form of monkey or primate that we know have been in existence for

20 million years or more. And the pattern of primate evolution as a whole is complex but seems to be driven largely by the way the continents have moved over time in the very long distance past. And then more recently by the way in which the environment has changed and the climate has changed.

And I think the best way of thinking about this sort of move from apes to the first humans is that the apes came under more and more pressure. Apes like to live in forests, they like to live in relatively moist environments, and that's what changed. So we see during the last 10 million years or so a gradual move in environments, and the apes had to adapt to that. and humans were, as it were, one way they survived. Leslie Isle, why is Australopithecus anamensis seen as the first of what could we call the human line?

What characteristics distinguish animus? There's one very important characteristic that distinguishes the Australopithecines, and this is their ability to walk effectively on two legs. The Australopithecines in general. What dates are we talking about? How long ago are we talking about now? Oh, we're talking a little over four million years. Australopithecus animensis is the first of the Australopithecines,

and it dates at about 4.1 million years. So you say this was the first lot to walk. Why is that so significant? Well, it's significant because none of the other primates walk on two legs. It seems to be terribly significant in the course of human evolution. But does it make you go fast? Can you hunt better? What does it do? What does it do? That's true to get on in life as you were.

There's a variety of things that it does for us. So, I mean, one idea is that it actually helps us to keep our temperature down. It's an adaptation to thermoregulation. Because your body's further from the ground? Well, it keeps your bodies further from the ground, but it also allows us to expose less of our surface area to the sun. And because of this, we don't seem to absorb as much heat. So we can keep our total body temperature.

temperature is a bit lower. The thermoregulatory idea is one idea, but another one is also that it allows us to move more efficiently, that we can move from point A to point B without using as much energy as a four-footed animal would. And then there's the ideas that we can carry things, we can see longer distances, but I think that either the thermoregulatory or the locomotive efficiency hypotheses are probably what the answer was at the time. that point. Mark Robert, you're a field archaeologist and Maeve Leakey discovered the first animensis fossil fairly recently. Are you happy about the way anthropologists seize upon these very few finds and work them into quite elaborate stages in the story of human evolution?

Well, I think in many cases that's a logical progression. It's not always the case that the archaeologists aren't also the anthropologists, the people that actually study the bones that they've excavated. In other cases, as you intimate, the archaeologists find the bones, but the actual study of the bones and the complexity of that study, depending on what one's specialist is, is often too great for an individual. So I don't have a particular problem, for example, if I found a bone handing it on, that's not my area of speciality, but I'd probably like it to be looked at by someone in my team

who was sort of within the team, so we would aim to have somebody on any given project whose speciality was fossil. Yes, but are you at all, does it bother you in the slightest that just a few bones can fill an enormous space in time? On the whole, one would be happy. Well, I would be happy with the filling of time like that, because simply there is such a vacuum

and really these finds get moved on things change people accept that you can have a find it's defined it may occupy a large space of time five years later along comes something else

and that one gets knocked back and it's just that we're dealing with so little material that I don't think that it's a particular problem Robert Furley certainly there is very little material but I think one of the things one should recognize is the enormous achievement really of the last century

of massively increasing the amount of material that there is. If we went back to 1900, you could count the number of fossil humans probably on one or maybe two hands. And now there are probably well over 2,000 individual specimens covering that 5 million year period, so it's still not a vast sample. So I think that while we're still working in a world in which there's a lot of time and not much material. The amount of material is still vastly greater

than either I think most people realize or that there was just a few years ago and that's a result of enormous amounts of fieldwork and these big multidisciplinary teams that are now out there looking for new finds. Well, just one more on this point. Lizzie Ayah, are you convinced that, say, from 2000 specimens remaining, you can construct a story of 5 million years?

Of course. It's not the number. It's what the individual bones tell us about the adaptations of those early humans. And the importance about the earliest discoveries, the animensis discoveries, is that you have lower leg bones there that indisputedly tell us

that those individuals are walking on two feet. And what this does is allow us to root this important adaptation in time. Mike Roberts, can we come back to, as it were, the basics, the way this thing starts, which is to do a digging, and you're a digger, a very famous digger, with your Boxgrove Man and so on and so forth. How does a field archaeologist know where to dig? The leaky family in Africa have been extraordinary successful.

They seem to know very much where to go. You were extraordinary successful with Boxgrove Man and all, and the multitude of things you found around there. Is it the accident in Northern Europe, particularly of there being a handy quarry, or what is it? Well, in Northern Europe, you're quite correct. The quarries, without the quarries, without the aggregates industry, we'd have had very, very few sites. In the northern hemisphere, after the glacations and so on,

a lot of our finds up here tend to be very deep. They're buried deeply as a result of higher sea levels, of rivers downcutting, for example, the famous sites along the Thames, like Swanscombe. These are deeply buried sites, whereas I think in Africa, for example, in southern Spain, one can almost walk or one can walk about and pick things up off the surface.

The depth of the Pleistocene sediments in many instances is not as great as it is here. So we need accidents like rivers and quarries to actually get down to the layers that contain the archaeology. Of course, there are many more quarries that go through these deposits that have nothing there. But the basis of what you were saying is that one needs, first of all, to be looking in deposits of the right age and the geology of the right age.

And then you need to be looking for conditions of preservation, looking at the type of sediments that are going to preserve your stone tools, your fossil remains. Is it hit emisser though? I mean do you accidentally hit on... I'm not trying to be frivolous here. I mean, you just hit on this particular quarry that delivers this, or is there a map that you people have that says, well, look, we think that they were in the southeast of England at that time,

although it wasn't England, it wasn't. But they were around that place at that time in these numbers. Which is it? It happens both ways, but now in this day and age we do have a map. So we have a project that was devised, in the late 80s, early 90s, which has mapped all the sort of fine spots from our period across England. Also, there's sort of local knowledge in as much as we know, for example,

if you take the Boxgrove case, that we know that people, when these quarries were hand-dug, even in the early part of the last century, that workmen found stone tools there. So it's been current in the literature for quite some while. Robert Filman. I think there's another aspect too, which is in the sense we know where not to look as much as where to look, which is not to do with the geology. For example, we know that if we're after the first humans, looking in South America is not going to produce them because there are no apes in South America.

We're not going to find them in Australia. So, as it were, the record of our evolutionary history is written in the biology of the apes and the primates. And that sets us with a sort of series of expectations. And indeed, I mean, Darwin himself said, go to Africa, look for the first humans in Africa because our closest relatives are there. So there are, as well, biological clues as to where to look, as well as geological factors as well, so that people focus their attention where they think there are going to be interesting problems. As Einstein, about two and a half million years ago, homo habilis evolves. What's the significance of homo habilis? Homo habilis is very controversial right now

because a number of anthropologists would actually like to call it Australopithecus habilis. Why is that controversial to the uninitiative? Well, why it's controversial is that for many years Homo Habilis was seen as the first member of our own genus, Homo. And this meant that it had made a significant jump. It had a different type of adaptation than Australopithecus. Now, this early interpretation was based on estimates of brain size and tool-using ability.

What the mystery was, though, is that a few years ago, a skeleton of Homo Habilis was found, and the skeleton was surprisingly similar to Australopithecus. And what this did was raise the question in a lot of people's minds that Homo Havlis really wasn't Homo. It really hadn't developed the complex of characteristics that we would recognize as a significant advancement over the earlier Australopithecines. So therefore, the development of what we became, the significant development came later then.

Yes, this is exactly the question, and it raises the issues of how we actually define ourselves. What we see is the major differences between Australopithecines are alternatives who are no longer extent. And early homo, where we think had evolved a number of features, increased intelligence, increased sophistication of tool use, increased efficiency and movement.

In other words, early homo was the first species or the first type of early humans that developed the complex of biological adaptations that allowed it to successfully move out of Africa and colonize the rest of Europe and Eurasia. So we're still looking for where that crucial turn happened, that business where they became like us. We're still, because it's now in dispute about her mohabitists. Robert Foley, would you like to take this?

Where are we locating that? Two and a half million, two, and what happened to make, you say one of your pieces that actually if we look back on evolution, we would see nothing very much happening for a very long time. I rather like that. But something did happen at certain times. So when and how and why?

Just for a start. Why don't we have a difficult question? I think trying to find out the when is becoming easier. Now that we've got more fossils, we've got a period from say four, three, two million years ago where you've got lots of, really what I think of as bipedal apes, they're upright apes, and they're experimenting with different ways of surviving in different habitats.

And then one of them, and we don't necessarily know very clearly which one comes up with a new trick in evolution. It's found a new way of solving the problems of living in its environment, and that new way seems to have involved being more intelligent, and I say that because they have larger brains. When did the larger brains develop?

Probably they start to develop around about two million years ago. So it wasn't you put it later than homohabelists then? I would put it a little bit later than homo habilis. Why did they develop? Well, that's an interesting question. I'm not trying to avoid it. this one. The context of this is the beginnings of major climatic

change. I mean, we're moving into the ice ages. I mean, most of the last 60 million years have been really quite warm. I mean, we hardly need to say in England. This is not a warm place anymore. And for the last two million years, it's been getting colder. And Africa was getting drier. So I think it was getting a tougher and tougher place to live. And for the Australopithecines, they found a way of surviving by walking upright,

by actually doing strange things with their teeth and getting big large teeth which allowed them to grind lots of coarse food. I think what happens with Homo is they found a new trick. And my own view is that that trick was hunting and eating meat. And that that enabled them to get a better quality of food. You know, here was lots of animals out there which could be hunted. And that in turn allows them to have a large brain. Because with brains, we think of all the benefits.

You know, they allow us to sit in BBC studios and say things. but they also are very costly, metabolically very costly. And so they're tied into the ecology. It's 22 times, isn't it, the unit compared with muscles to keep it going? It's extraordinarily expensive. And so that side of it is we've got the reasons why they need to have larger brains, which could be to do with intelligent enough to make tools to hunt, and then having the right diet and quality of food,

particularly for the mothers, which allows them to grow those large brains. That seems to happen about 2 million years ago. Would you go along with that, Leslie Ayla? Oh, very definitely. But I think there is also something we're missing in the meat eating and the large brain. Because with early homo, and I'm referring now to early homo erectus that appeared somewhere around 2 million years ago, they also were 50% bigger than the Australopithocytes.

So it was a combination of large body size and large brain size. and the reason for this large body size, it seemed to have been essential in terms of survival in the open savannah, much hotter climate. And it was essential primarily because it helped them from dehydrating. So they would need more water when they came to drink, but they could also survive for longer between waterholes. Now, I agree with Rob that I think that meat eating was tremendously important

and the ability to hunt and also, of course, the scavenge. But I'm convinced that they would have been exploiting underground storage organs also. These would be yams, potatoes, this type of tuber. And it would be this vegetable food that would give them the calories to grow and maintain the large body. But they would have needed the meat, and particularly the long-chain fatty acids, that are essential building blocks for large brains.

So in my mind it would be the combination of exploitation of animal-based food resources plus the underground storage organs that would give them the essential calories to maintain this large body mass. Mark Roberts, as an archaeologist, can you begin to detect a carnivorous diet in any particular species? Well, the difference that occupies the minds of most archaeologists is the difference between scavenged assemblages of bones. what constitutes a sort of scavenging from skeletal remains and what actually constitutes access to more or less complete carcasses.

And that obviously can happen either through hunting or through another particular type of scavenging, which is termed confrontational scavenging, whereby you allow another creature more suited to the killing than you to make the kill, but then through your sort of organisation, you drive them away. That's confrontational scavenging. And obviously that's very difficult to tell apart from hunting, because if you have access to fresh carcasses,

we're looking for skinning marks and cut marks and so on. But in your boxgrove man, you discovered that boxedrow of man had not only got hold of rhinoceroses, but cut them up rather expertly and so forth, which said a lot about, actually added to what Leslie was saying. it's not just the bones of, as it were, the hominids, it's the other bones and the markings on them. Yes, and those other bones allow us to have some sort of handle on their behavioural repertoire,

what they were able to do, the way that they actually operated it, and the sort of variation in the way that they operated. Hunting, the emergence of hunting, I mean, the role of it in human evolution is still, I think, open to debate. We have a stage, at one stage, we have about 15, at least 15 species, sort of like each other knocking about. We're talking about, what, 2 million years ago still,

we're going to have a rapid fast forward quite soon, but let's just finish this 2 million years ago, and what's the significance of that? Well, I think the significance is, as well, the picture of evolution that it shows in general, that I think when people think of evolution as being this kind of ladder up which humans have diligently climbed,

more and more towards us. The fact that certainly the first three million years of our evolution doesn't show that, it shows, as it were, that it's more a process of experimentation. Little populations get separated from others. They specialize, they become unique and different, not in major ways, just in small ways. And you end up with what biologists call an adaptive radiation. So instead of a ladder... Can we give us one to a specific example?

Of the particular species. Well, I mean, if you look, say, in Africa, let's say two million years ago, you've got in East Africa, you've got something called Australopithecus Boisei, which is extraordinary creature in some ways because it's got this enormous face and very, very big molars,

its back teeth are something like three times the size of ours, and then a massive jaw hanging off the bottom of it, and in order to move the jaw, it's then got to build up the muscles on its skull, so it has what looks like the sort of keel of a sailing boat running along the top of its skull, as you get variants of that and you can find a similar form in South Africa.

So it's this diversity that you see. And I think that's not surprising. You look at any group of animals as they evolve. That's exactly what they do. So you can look at the cats and they've diversified and gone into all sorts of lions and lynxes and tigers and leopards, different ways of surviving.

And our ancestors obviously did the same thing. And in a sense, the surprise is that once you come into later human evolution, all those other forms become extinct. And I think extinction is important. And then we get a thinning down of the bush. It's much simpler after that. The bush being the way that things develop rather linearly, the bush of society.

Those are I? Well, I don't think that it may have been quite the surprise that Rob is suggesting because I think that early home will probably hit on a trick. and that trick was a change in social organization and it was a change in social organization that allowed them to exploit the new food resources because something would be missed.

Which new food resources? That this would be either hunting or underground stories. But we're still with that, yeah. The change in food was fundamental to the evolution of the genus Homo. And one thing that we forget is that in the apes and the chimpanzees and gorillas, they very rarely share food.

And if you look at the diet from the point of view of the kids in chimpanzees, as soon as a infant is weaned, he or she is on their own. They have to gather their own food. Now, if you're moving into an environment where you no longer have the food resources that you have in the forest, where you're moving into hunting or you're moving into digging the underground storage organs, that food isn't going to be available to those kids, that they're going to need help from the adults in order to survive

to gain the benefit from those higher quality food resources. Now, how they did that would require a fundamental change in the way the societies were organized. A division of labor, really? Definitely a division of labor. What evidence have you got for when that evolved and how it evolved? Well, there's no tangible evidence for it. but we know that if we're talking about a change to meat eating,

and certainly in this time period, around 2 million years ago, we get evidence of animal food resources in the paleontological and archaeological sites. We know they were eating the meat. And if they were going to do this, they would have had to have shared the food with the young individuals. This would have freed them tremendously, because it would have allowed them to exploit habitats where there wasn't accessible food for the offspring.

And this would have allowed them to move out of Africa into different environments where there were different food resources. So the sharing of food was fundamental. It's quite appropriate that as we come towards the end of the program, we approach Homocipians. Can you just, Robert Foley, can you just fast forward us to about 100, 150? 50,000 years ago when homo sapiens began to be recognizable.

Yes, I think in a way it's the most exciting part of the whole story because we can talk forever about Australopithecines and have lots of Latin names to juggle around. But the exciting thing is that as this homo, this larger brain creature, spreads around the world over the last million years, it's quite clear now that only a very small part of it evolves into modern humans. So you've got these Neanderthals and Heidelbergs and things around the world, but it's only now we think in Africa that a very small population

evolved into what we call anatomically modern humans, homo sapiens, in other words, with our particular shaped skull and our rather slim, grass-isle bodies. And that happened about 150,000 years ago. And it happened probably, again, as a result of all this climatic change, that around about then, the world was gripped by probably the coldest period. There's been for millions of years, a massive ice age. Africa became dry, probably populations died out.

And there's where a small isolated population evolved into us, maybe had some new behavior, and then it spread around. When we come to 150 hours ago, have we got the things that we think distinguished us? Have we got, Leslie, have we got language? which, have a good abstract thought. Can we think hypothetically? Do we know what we were like then? Or are we beginning to be like what we are now

and you took another 100 or so thousand years to get cracking? Well, this is a really difficult question because all we have are actually the bones and we can tell from, say, that the shape and size of the skull that their brain size was identical to ours. Where the question comes is evidence for abstract thought. And if we go back, say, 150,000, years ago, we're back prior to the time of the cave paintings, which is the evidence that

most people take that individuals were definitely thinking like ourselves. The oldest cave paintings are about 30 to 36,000 years in Europe now. But if we go back in Africa to 150,000, we begin to see tantalizing bits of evidence, such as the inclusion of red ochre in the sites. And many people think that this red ochre is a definite first sign of the symbolic ability that our ancestors had. Body decoration. Body decoration, definitely perhaps that they were using it to paint on artifacts and we just haven't found this yet. But it's considered to be a very

important aspect of these early archaeological sites. Do you think it's rather dangerous that a single species is now over the planet? Do you think? I mean, does it rather dangerous that we just down to one, and then there's what's like the 10 green bottles, isn't it really? Not so much that there's only one species. What's frighteninging is that we're so successful at reproduction. And the question is how long we can sustain this rapid population expansion. Robert Perl?

Yes, I think having 6 billion people means at the moment we're a fairly safe species. I mean, remember that our Homo sapiens at one point probably consisted of less than 50,000 people. that bottleneck out of which we emerged. So I think that as long as we have a large population, we'll be all right. Well, there you go. Thank you very much to Leslie Ailo, to Robert Foley, and to Mark Roberts, and to you 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.co.com.uk forward slash radio 4.