In Our Time - The Whale - A History

Episode Date: May 21, 2009

Melvyn Bragg and guests Steve Jones, Bill Amos and Eleanor Weston discuss the evolutionary history of the whale. The ancestor of all whales alive today was a small, land-based mammal with cloven hoofs, perhaps like a pig or a big mole. How this creature developed into the celebrated leviathan of the deep is one of the more extraordinary stories in the canon of evolution. The whale has undergone vast changes in size, has moved from land to water, lost its legs and developed specialised features such as filter feeding and echo location. How it achieved this is an exemplar of how evolution works and how natural selection can impose extreme changes on the body shape and abilities of living things. How the story of the whales was pieced together also reveals the various forms of evidence - from fossils to molecules - that we now use to understand the ancestry of life on Earth.Steve Jones is Professor of Genetics at University College London; Eleanor Weston is a mammalian palaeontologist at the Natural History Museum, London; Bill Amos is Professor of Evolutionary Genetics at Cambridge University.

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 four. I hope you enjoy the programme. Hello, of all the Wales in literature, the most famous is Moby Dick, described by Herman Melville. Moby Dick moved on, still withholding from sight the full terrors of his submerged trunk,

entirely hiding the wretched hideousness of his jaw. But soon the forepart of him slowly rose from the water, and warningly waved his bannard flukes in the air, the grand god revealed himself, sounded and went out of sight. Melbourne's novel is one of drama and grim portent, but more extraordinary is the story of the whale itself. For the manner in which the whale has evolved is among the finest exemplars of the changes evolution can bring to bear upon life on earth.

With me to discuss the evolutionary history of the whale, are Eleanor Weston, a mammalian paleontologist at the Natural History Museum in London, Bill Amos, Professor of Evolutionary Genetics at Cambridge University, and Steve Jones, Professor of Genetics at University College London. Steve Jones, can you give us some context for the beginnings of what turned into the whale? I think whale, as well as being a sort of a magnificent creature and almost a swimming metaphor, as well Melville uses him, is a classic example of what might happen to humans if we landed on a new planet. because the whales were the first mammals really to go into the sea.

And the sea was then, 65 million years ago or a bit earlier than that, the sea was then more or less empty. It had been pulsing with life with the death of the dinosaurs at that time. Many of the giant predatory lizards that were in the sea had disappeared. So there was an empty world waiting to be experienced. And in the very early days of whale evolution, animals perhaps a little bit like seals appeared and then you can really almost see step by step now

in this new world which they'd entered there was endless ecological niches as we would say were available endless new ways of life and they very very rapidly took advantage of those and developed into enormous creatures into creatures of medium size into rather small creatures there's a rather interesting new piece of information which shows how astonishing the whale actually is

I'm sure most people listen to this program have heard about the amazingly well-preserved early primate of 47 million years ago that turned up two or three days ago. And looking at that fossil tells us how boring, our own evolution has been, compared to that of the whale. Because when that primate was hanging around, what the ancestors of whales were like were actually land animals, more or less,

or land animals that occasionally went into the sea. So all that's happened to us is we've grown a bit, and a little bit smarter. these predatory metal and animals in just 50 million years or so have become the largest creature, largest mammal ever to have lived. And that's quite something. So, you know, being a whale is quite impressive, but quite new. Can you tell us about artiodactyls?

Well, they're the hoofed creatures. And they've been well known. Of course, in Darwin's time, and indeed until quite recently, in fact, even now, what most biologists did was to try and make trees of relatedness among different creatures. Comparative anatomy, as it was called. It's called molecular genetics now, but it's the same stuff with a lot more money. And they could draw

quite effective and trustworthy trees that showed that humans and chimpanzees were related, that cows, pigs and deer were related. Oddly enough, animals with hooves, that last group. And oddly enough, until the 1940s, if you looked at the classic trees of mammal-relatedness in all the textbooks, it all fitted together more or less convincingly,

apart from the whales, which didn't seem to fit anywhere. They certainly don't have any hooves and didn't last time I looked. And we knew almost nothing then, 40 years ago, about their fossil record. We knew absolutely nothing about their molecular genetics, about their DNA.

And in just half a century or so of research, they've changed from a complete evolutionary enigma to perhaps the most perfect example of Darwin's theory as illustrated by fossils, by genes, and by the behavior of living creatures that we possess. That's why the reason we're concentrating on, because of the word you use, the perfect example.

Can we just briefly introduce us to the fossil evidence? We'll be coming back to this in more detail later in the programme, but just as an introductory, David, about the fossil evidence available. I think the fossil evidence is particularly impressive, and it's also particularly emblematic, because some of the earliest fossils of Wales were found, not on the seashore, but high up in the Himalayas. And when you think about it, that's completely startling.

It is in fact the case at the summit of Everest, not very long ago, was actually at the bottom of the deep ocean. And the reason why Everest is so tall, of course, is because we now know, as Darwin didn't, that there are plates across the world which are crashing into each other, and there are oceans which have appeared and disappeared sometimes more than once. And the first whale called Pachisetus was found in Pakistan, in the mountains of Pakistan, dates from something like 50 million euros a bit more years ago. it was a small creature that lived part of the time of land, part of the time in the sea, and was really the first hint of where whales actually fit in the fossil record. Somewhere remarkably close, as it happens, to the ancestors of modern hippopotamite. Anna Weston, so we have a mammal there.

We're beginning to think that it might be going into, just over 50 million years ago, partly on land, partly on water. Can you tell us about the state it might have been in at that time from a fossil called ambulocetus? Yes, well, ambulocetus, if you like, might be one step on from the very earliest whale, which you mentioned there, Pachocetus. And that was because it was clearly amphibious. In fact, it's been referred to as the walking whale because it had four limbs that clearly could support itself on land. in other words, the legs were still attached to the backbone. But there was clear evidence that this animal lived in water.

What is the clear evidence? Well, for instance, an extraordinary development of the foot was that it was extremely long and broadened. So it actually acted a bit like a paddle. But the paddle was really just in the hind legs. So I suppose this animal was more like an otter when you think about how they use their hind legs. but also the backbone was very flexible.

There's evidence that it was already moving up and down, like modern whales, you know, that they have a very distinctive way of swimming where the tail with a tail fluke that goes up and down, which is different to fish. So that was also some traces of that were in this early amphibious whale. But we do still have evidence that it would have probably come out on land to maybe feed, that's slightly controversial, but perhaps give birth. And yet it's found, geologically speaking, in sediments that are indeed marine.

So ambilocetus was one step on from the earliest whales, which we actually do find both in freshwater, the fossils are found in freshwater sediments and marine sediments. So we're seeing some transition, if you like, to life in water. We're still talking millions of years and Steve introduced us to 50 or 60 million years ago and now you're sort of 40 or 50 million years ago.

I forgot to say the we're now, Ambio Cetis is still very early. It's about 49 million years ago whereas the earliest packer cites examples which we think we call whales are roughly around 50 million. I think the very earliest is 53.

So it's quite a quick transition in terms of evolution. You know, we're only talking about a million years where you've got quite well-developed amphibious traits appearing. Can you tell us about fossils called

Basilosaurids and how they fit into this story? I'm just trying to get the sort of outline pattern, a little map before we go back and go in detail. Well, Basilosaurus was about 10 million years later. They found these spectacular articular skeletons of what you might call a sea serpent, you know, initially that that's what they looked like. So about 38, 39 million years ago.

Yes. Yes, yeah. And they were clearly marine animals, almost, almost, I mean, fully adapted to life and water. And they would have had what we believe is a tail fluke and moved around. But what was striking about them is they still had legs, very small legs that were detached from their backbone, that were, if you like, vestigial, but they had still some evidence that they functioned. You know, there was a locking knee and muscle attachments. And they've actually thought, well, these legs clearly couldn't have supported the animal on land.

So perhaps they were used to assist with something like copulation or... But I suppose what's interesting is you have this remnant... As guiding factors in the copulat. Yes, yeah. But you have, and it's an external leg, whereas I think today in modern Wales, Internally, we have a remnant of evidence to suggest that they had legs, but these still had these.

I think we're only talking about something like 18 inch long legs compared to a 40-foot-long animal, you know, ridiculous. But it's still interesting in the story of transition. How do you know it was 40-foot-long from a fossil? Well, they've got, the most spectacular skeletons have been found in Egypt, which was actually thought believed to be the southern shores of an ancient ocean.

So that's why they've got some very good fossils. And I think they're so well preserved. They can estimate from working out all of different segments of the backbone being preserved. So they can determine things like that. Bill Amos, we're getting there, but they're not yet fully aquatic, really.

They've had hooves. Their legs have got very short. They're bibvious, but they're not fully aquatic. Now, about 30 million years ago, as I understand it, they became fully aquatic. Can you tell us how that happened and what the whale had to do in order to enable that to happen? Well, I think Ellen has already described a really fully aquatic form. When your back legs are only 18 inches long and your body's 40 foot long, you're going to struggle to do much on land at all.

And they're already developing flipper-like forelimbs, which are necessary for swimming. Indeed, you're developing flipper-like fall-in from, how long does it take? The evidence seems to suggest that all this happened incredibly quickly. Yeah, but incredibly quickly for you. Incredibly quickly would be of the order of one, two, three million years. I think once you, as it were, dip, you remove yourself from the land to the point where you're spending your entire life at sea, which is the main transition, which, for example, seals have failed to. to do, seals still have to come ashore to breed, whereas the whales can give birth in the water.

As soon as you do that, you lose the necessity for retaining your land locomotion, and you can go from, instead of having fall limbs which would have supported your weight and helped you sort of move around like seals do, you can have them as proper flippers and you can go over much more to the fish-like form and be able to be much more efficient when you're swimming. So what happens in the fish-like form? and what other changes are they? It's in the sea. The legs are beginning to, well, they're very small then, and presumably they're getting smaller and smaller and turning into flippers.

What else happens? How does it turn from the mammal into, well, it's still a mammal, how does it turn into the whale, into the whale that we know? Well, all the other adaptations that a seal might like to have, so, for example, a tail fluke. Now, a tail fluke would be absolutely hopeless on land. It would get in the way whilst you were trying to haul yourself around on the shore. tail fluke is by far the most efficient way of swimming compared with seals swim pretty well

but they're nothing to a dolphin and so as soon as you can have a tail fluke you can become much more streamlined and dolphin is a family of Wales and the dolphin is one of the members of the family of Wales so you can certainly you don't want your back legs hanging out they're doing absolutely nothing the driving force is produced by your tail fluke

so you can get rid of those you don't want extra drag and then at the front just like an aircraft has wings as it were to and flaps to steer. The whales have these flippers which are used really to direct the way in which it's moving with the main propulsion coming from the tail and these incredibly strong dorsal muscles that lie along the back

that allow it to flex its back in a vertical position. Can you describe the tail fluke and tell us exactly what you're talking about with the tail fluke in a bit more detail? Well the tail fluke is this large classic sort of it's a plate, it's made out of of connective tissue. It's very robust, but it's rather like a very thick piece of neoprene,

and it's a specialisation that they've developed. It's, as it were, grown out from the side of the skin. I don't think, because it's soft tissue, it contains no bones beyond the end of the vertebra, it's not really preserved. So we speculate that this is what they had, but we don't know the development of it too much. Eleanor may know more.

No, but paleontologists have looked at the pattern in which the size of the vertebrae, which are part of the backbones, and they can see that, for instance, in basilosaurus, that it's got the right arrangement that would indicate that it had a tail fluke. Just that's by comparing it with what we know in modern. Sorry, I'm sorry, just about, and what's the size of this? This drives them. This is the driving, this is the engine, isn't it, yes.

Yeah, I mean, I don't think, again, we don't know the development. We may be able to infer when they had flukes, but we don't know what the early flukes looked like. Presumably it was something like, for example, beavers have a flat tail that they use, at least part in propulsion. We can imagine that it's much easier to generate a slight flattening rather than a lovely fully formed fluke. The fact is that if you look at fishes' tails,

if you look at all other swimming organisms that use a tail fluke as a method of propulsion, it tends to be roughly the same shape. And physicists, I'm sure, will tell you that that. that's the most efficient shape that you can have. So you start off with something that helps you generate a bit more force by a flattening of the tail, and then the genes wonderfully managed to come together to anything that enhances the efficiency will be selected,

and so we can imagine that a fairly rapid transition to the modern fluke. These adaptations, turning in a torpedo shape, the leg's going, the fluke developing and going up and down, so they can drive forward. They didn't evolve gills. Why do you think that? This is, well... Didn't happen. Basically, you can think of evolution as driving change

along a progressive series of steps. And you can have, as it were, what we call adaptive peaks. These are states which are clearly nicely formed, and they work really nicely. Now, then if you want to breathe underwater, there are two ways of doing it, really. is that you can take oxygen from the water and you can use gills as fishes do

and the other is you can retain lungs and process air which ties you to the surface but it's such a completely different mechanism and evolution needs intermediary steps it can't just suddenly flip from lungs to gills so in order to get

from one to the other would require you in some way releasing your need to go and fill your lungs with air and at the same time with a high metabolism and a high oxygen requirement, swap your mechanism over, and that to me is pretty much completely implausible. I mean, evolution is really, on natural selection, is really nothing more than a series of successful mistakes. And you're basically, you know, every animal is a living fossil of all its

ancestors. And it's very hard to get from the summit of Everest to the summit of Kanjinjonga for two excellent places to be without going down the valley in between them. And evolution has never managed to make the journey. What's interesting about the more, the more morphological, the shape and size evolution of whales, which is striking and is shown in the fossil record, is that when you look at the living creatures, the tips of the evolutionary branches, actually you can see precisely the same thing happening at the molecular level. For instance, we've talked about swimming and diving. Whales can do astonishing things.

Spirm whales can stay down for more than an hour. They can dive to pitch blackness, a mile below the surface. How do they do that? They've got, in their muscles, they've got a special protein, which, we have a much feebler version of called myoglobin, which can soak up massive quantities of oxygen when they breathe in, and they're much more efficient at turning over the air in their lungs than we are. They can expel 85% of it and replace it.

We can only expel about a sixth of it, and this protein will hold on to oxygen for far longer than ours will, so it will slowly let it out when they're deep down below. So that the shape evolution, the stuff that's so much impressed, Herman Melville, is accompanied by equally striking changes, the skin, as it were. And of course, in general, the fossils don't tell us that, but the living fossils, the animals themselves, really reinforce in the most astonishing way, the lesson that comes from the rocks.

This discovery, or the whale shared an ancestor with the hippopotamus, can you explain how molecular evidence gets us thirsty? Well, molecular biology is really exactly what, it's like dissection, but you're dissecting with a much sharper knife. you're breaking the animal not into parts of its guts or cutting up its vertebrae, you're actually looking at the building blocks of the body. And because the building blocks, the chemical blocks, are the same in all creatures. Every one of us is almost like a whale, and so is a bacterium.

You can actually use the arrangement of those four DNA bases, as they're called, to look at patterns of kinship. And if you do that, what's really quite startling, if you look at the mammals as a whole, is how well the molecular tree fits in general. with the trees traditionally made from fossils and from dissection of bodies. Wales are kind of special because when we started looking at them, well, people started looking at them from the DNA point of view,

there really wasn't much idea where they fitted. And it turned out that actually, rather surprisingly, they fitted close to a shared ancestor with a hippopotamus. And once you see that, of course, like everything, it's the benefit of hindsight. It's obvious, right? Hippopotam-I... It isn't all that obvious to us to our own.

It is, I mean, hippopotam... So can you just tell us how obvious it is? Well, hippopotamai live, spend a lot of their time in water. Okay, they don't have... Like whales. Like an early ancestor of a whale. They don't have any hair like whales. They keep their testicles in a convenient bag outside the body.

So they keep it, unlike ourselves, who keeps their testicles in a convenient bag outside the body, their testicles are internal like whale testicles are. They communicate underwater, hippopotamai, by squeaking and squealing, just like whales do. So you can, you know, once you've got the clue, it all begins to fit together. And the most astonishing first piece of evidence, which tied the hippopotamite of whales, must be 15 years ago now, was the discovery that Wales hippopotamai and some of the hoof mammals

have within their DNA inserted three or four little virus-like particles, which are not present in many other mammals, suggesting that they descend from a common ancestor which had that virus-lossed particle, And the virus looks rather like the AIDS virus. So suddenly evolution joins together the tiniest creature and the most enormous. And that's kind of moving almost. Alan Weston, can we develop that?

The discovery of the ankle bone, this hippopotamus thing, which Steve Jones has been taught about molecular evidence, are other sources of evidence not quite as certain? Well, I guess the story we have from fossils, Firstly, what we, as a paleontologist, might have assumed, would say, the relationship between the hippo and the whale, is that they looked alike simply because they both lived in water. So they, for in other words, they could have evolved the specialities

that you were talking about independently, much later in time. But one thing that seems to be becoming clear is that whales have come or are artadactyls. You know, we mentioned before that they are clover, hoofed mammals and they're things like cows, sheep, camels even, deer,

all those sorts of things. And we just didn't know what is the closest, what was the ancestor of the whale, what was it related to? But if we speculate that a whale is an artadactile, the artadactiles are

defined by an anklebone, something that they all share, which is this rather strange, it allows, it meant in development that the animal could be very flexible because the bone had two trache-tricleated, which just means like two cottony like facets on both ends, which meant that it was highly developed and able to run. And it meant also that this animal, the movement would have been restricted to one plane. And this was an innovation in going back sort of 50 million or years ago

that animals had developed this ability to move quickly and be agile. And all of these clove and hoofed mammals have this character. So when molecular data suggested, quite surprisingly, that the hippopotamus might be the closest relative to the whale,

they obviously asked, well, have the early whales got these ankle bones? Would that be the ultimate proof that the fossil records could demonstrate. And of course, whales today have lost their hind legs. So when evolutionary biologists want to compare characters, it's very, very difficult because the leg's obviously gone. But the very early whales, Pachocetids, that we mentioned before,

did, we've now found ankle bones. But not just Pachetis and Ambulocetis and one slightly later, that we believe are indeed, like artadactiles, although the story isn't quite as straightforward as that, because these ankle bones are very primitive in the sense that they're probably more primitive than any other known animal. And Ben Amosso, we've got the ankle bones, although that's under certain, not so much dispute, but it isn't quite as clear in Alan's mind as it might seem.

Can you explain how the whales reused things? I think it's called transfer of function and maybe concentrate on the whale's jaw mentioned by Melville at the beginning of the programme, turning into the sonic boom. Well, obviously when you go from the land into the water, the whole hearing process changes dramatically and you go from a system where you've got a very light medium

which transmit sounds very well to much denser medium. And what you find is that in the earliest fossils, there's now a fossil one of the Raoelids I believe which actually has the year bone which suggests that it could function both on land, in air and underwater

very rapidly as soon as you go into the water system they need to be able to hear underwater and the whole year becomes much the year bones become much heavier and much denser and much more adapt to transmitting sound underwater and it's at this

point that we believe that they start thinking about actually developing the whole system that we know that whales have today, which is this method of effectively sonar, making squeaks and whistles and listening for the rebounding of those, and also for communication. Can you tell us how that works? Can you give us some detail about how that works? So they make these squeaks and whistles. I've always thought of it rather, because I know so little, rather romantically in that, these great booms going across half an ocean

and this sort of orchestra of whale sounds under the... No, it doesn't like that, is it? You say, squeaks and whistles, squeaks and whistles takes me down 17 things. It's astonishing diversity of sounds that whales are capable of making. And they make them for many, many different reasons. So, for example, there are the very low sounds that they use, and there's evidence I know some colleagues of mine happen to be two groups

were following different fin whales, 500 miles apart. And one of them started calling, and the other one, they know only, just coincidentally, they were following them both, and the other one started turning, and they ended up coming together and meeting. So they'd spoken to each other in some sense, communicated. 500 miles. Is that the record? I'm not being silly. I mean, is there any evidence that's the sort of distance that Wales can communicate under water, because sound travels so well, particularly if you use the right frequency. And so this ability to communicate, this is why everybody got so worried when the Navy started,

using these incredibly loud noises for all their various nefarious purposes for tracking ships, etc. There was a concern that whales would be unable to hear each other. And, I mean, A, you could damage their very sensitive hearing. They're designed to pick up somebody else speaking a long way away. So I'll actually turn towards a submarine if we're not careful. Well, certainly there's evidence that whales have been certainly damaged, if not killed, by the power of some of the sonic booms that humans are making underwater.

But that's just one kind of use. So they also use the sound in terms of locating objects. And experiments on dolphins in captivity show that they can discriminate incredibly finely between different shapes and different sizes of object. And you only have to see dolphins in captivity going off and chasing things and the ability to catch a moving fish.

They certainly don't use sight very effectively. using mainly the rebounding sonic sound, the very high-pitched whistles and things have very good over short ranges. They reflect off the fish. And in fact, there's even thought that they can stun fish and squid by making very intense sounds that they then focus. Many whales have a bulbous

front end, a sort of a large kind of a globe on the front of their heads. And this is mainly fatty tissue. The classic example is the sperm whale, this huge great what some people call the nose rather strangely, but it's sort of huge great square head that you see classically on Moby Dick. This is all contained with fat and it's thought that this acts as a lens to funnel sounds made in the breathing tubes and can produce very

highly directed sounds in front and potentially even stun the prey that they can then go and suck up. So in fact somebody once calculated that a sperm whale underwater is such a big object, 50, 60 tonnes, that in order to eat a squid, it's just not worth it turning because it takes so much energy to turn that you've got to have a certain size of squid before it becomes worthwhile. So you certainly can't afford to chase things. So this was quite a worry for scientists. 50 and 60 tonnes, that brings us back to the reality, Steve Jones. But let's go back to the fossils. Now, there's a sad line in your notes which, given you're such a champion of,

writer of, explainer about Darwin, that you say the fossil record can look anti-Darwinian. It must have cost you blood to write that sentence, do you? Yes, it's up for it. Darwin himself. Time says that. He has a whole chapter in the origin about the incompletes of the fossil

record. And it's led to endless arguments both for creationists. Well, you can't have an argument of the creationist. It led to endless loud, meaningless squeaks from creationists rather like a whale, but also within biology itself. It's clearly the case that at nearly all fossil records,

you do not get what Darwin would have liked, which is a slow, gradual transition from one form to another. And you can interpret that in two ways, the way that Darwin did, which is that actually most of the intermediate forms had been swept away by the accidents of time, and he has some very poetic stuff about working out, looking across from the north towns of Kent to the south towns of Kent,

and pointing out that once there was a mountain in between, them made a chalk which had been washed away with all its fossils. And you can see that in many ways, for example, if you go to the battlefields of the First World War and look for the corpses of the men that we know that were killed there less than a century ago, many of them carefully buried, they've nearly all gone. So the fossil record really is incomplete. But there's an alternative view, which Stephen Jay Gould was very attached to, which was actually what's really happening in the fossil record is long periods of not much happening. And then very rapid change is so rapid that you probably won't see them among the dead bones themselves.

It's Steve Gould, who was much criticised, people who didn't like the idea, said that was evolution by jerks. And then Gould came back and said, well, the alternative form was evolution by creeps. So you can see that biologists are just as childish than anybody else when it comes to arguing about the fossils. But the whales, I do think, give hope to us creeps. It does seem that we've got many of the intermediate forms. I think one of the most exciting recent,

discoveries, which sort of brings this story up to date, is that we now understand much more about the genes that are involved in development. And they've now, because we now know the genes that are involved with limb development, we can then go into Wales and ask what's happened to those genes. And there are two really exciting genes. There's one which is involved with the development of the hind limb, and a single mutation in this causes mice to lose their hind limb, such that the limbs become these tiny kind of primordial couple of bones in the body wall, which is exactly what they look like in whales. So it looks as if a single mutation can cause loss of hind limb, and this is, if you look at the whales, they all share the same mutation that the mice do.

And there's a second gene, which is, again, it causes problems in humans, which is where humans have a mutation which causes webbing between the fingers and often extra digits. which is exactly what you'd want if you had a paddle. Well, it turns out that whales have this mutation as well, and it's not the only mutation that develops the flipper, but it certainly shows you that the genetics can produce the sorts of forms that would be appropriate for aquatic life. Ananduelson, can I ask you, does the fact that unrelated creatures can look similar?

Is that a problem for paleontologists? Well, I think what you're getting out there is that, you can look similar not because you're through common ancestry you can look similar because you just adapt to a similar mode of life well everybody thought the well was a fish until a couple of years ago because it looked like a fish it's definitely a problem for paleontologists but in some ways it's also a problem when you look at relationships even using molecules with this idea that things can be reversed their function happens quite a bit but i do to come back to the fossil reference record a little bit. I do think that although we can make lots of predictions from our modern animals about how related they are, we still do have a remarkable, say, 60 million years' worth of evidence for types of animal, and you've got to still explain them. And it can also help us with what we sometimes call divergence time. You know, we know if a whale or something like a whale existed 50 million years ago that, you know, there's a common ancestor that's even earlier.

And I may be going off the point of it here, but I noticed when we were talking about the hippo and the whale being related, what you're really saying is that an animal that lived sort of 55 or 60 million years ago was a common ancestor, and it probably didn't look anything like either a hippopotamus or a whale. You're dealing with something completely different. So this whole, element, this dynamic time element, is very important to bring that into your understanding of these relationships. But you are right, during that time, all manner of things like a hippopotamus could have gone into water several times, you know, within 60 million years. I mean, it may not have done, and likewise, not just the hippopotamus, another artadactile, like one that you were

mentioning some of the early afterdactyls that lived in forests look very like what we have a term mouse deer or water shepherding today and they were semi-aquatic animals that we still live today but of course they independently evolved characters that would have

meant that they lived in water that would have been shared by whales and hippos and these mouse deer Steve Jones does do molecular do molecular investigations bring a different sort of light to bear on this? They do. They sometimes, molecular biologies are filled with insane self-confidence, I often think.

What happens in molecular biology, people get stunned by the amount of data they can generate quickly. And it's nowadays astounding. I mean, and I think biologists really are amazed by what's happening now. The rate at which we can generate DNA sequences is going up, has gone up over the last 10 years, by thousands of of times. So you have this wave of information that's coming forth, and it's fatally easy to look at your printout in the old days or put it in your computer, and to generate a family tree. But it's, in fact, until recently, people just would generate a tree of relatedness between whales and hippos and various other things without using any statistical tests at all.

And it turns out that actually there are millions of possible family trees, and it's quite hard to be sure which one's right, and very often we don't know which one's right. I think the whale and hippo one is pretty impressive. It's also the case that there tends to be an assumption among molecular biologists that all this change is purely random. It just happens. It's like a clock. It ticks away.

Mutations appear and then they disappear as the individuals who carry them die off for random reasons. That too is almost certainly not the case. You know, whales and ourselves each lack hair. But we don't lack hair because we share a recent common ancestor. we lack hair for different reasons, which are quite independent and driven by natural selection. So there's a lot of assumptions in molecular evolution which are not generally present in paleontology.

In palatology, you've got the bone, staring you in the face, defying you to understand how they fit together. In molecular biology, you have a lot of mathematics, and I'm very, very dubious about mathematics. Lemus, do you want to say something? Because I don't ask you a question if you don't. Well, it was carry on Steve's point, which is that these molecular trees work very nicely

when the evolution is progressing very nice and evenly in the creeping sort of way, as we discussed earlier. The problem is that with whales, and in fact with the whole mammalian radiation, is that when a group of animals gets an innovation, either becoming warm-blooded and furry like current mammals and giving birth to live young, or in terms of whales,

finding a whole new environment with all the exciting possibilities, what tends to happen is that they completely run wild and produce lots of different forms very quickly because there are lots of different things that they can do. And this produced what we call a star phylogeny, lots of lineages all arising over a very short period of time. And of course, because they arise over a short period of time, trying to find out which came first is very difficult

because all the branches at the base of the tree are very close together. and that's what's given rise to a lot of the controversy about the ways in which the different whale families are related to each other. Helena Weston, do you see limitations in the molecular evidence? I mean, there are limitations, but of course there's limitations in the fossil evidence. But I guess with the molecular evidence, what you've got to remember is that many of the species that existed are not, you're not alive to there. You can't get molecules from them. They're extinct. So actually, I've heard figures of, there's a ratio of, say, in whale evolution, of nine to one, whereby I'm not, nine, the majority representing extinct species.

So when you're looking at the degrees of relatedness with these animals, most of them don't exist. So your molecular data is only representing a tiny fraction of the species that evolved and are obviously all part of this evolutionary story. At this stage, Steve Jones, you started by saying it was a phenomenal and perfect example of evolution. I think you went. Can you just summarise and tell us why, and what we've heard,

is explaining to the listeners, why it's so phenomenal and why it's so perfect? Why are you, unusually for you, using superlatives? In some ways, because it all fell, it's like, you know, I don't know, it's like dealing a hand of cards, Suddenly all the right cards came out in the last 10 or 15 years. 20 or 30 years ago we knew almost nothing.

But now I think if you read the origin of species, which I actually do recommend, what Darwin did in the origin was to bring together bits of information which did not seem before the book to be related to each other. Stuff about pigeons, stuff about fossils, stuff about animal breeding, stuff about new kinds of creatures in different parts of the world. And people knew all this, but it didn't make a story.

and Darwin called the book one long argument. And what the whales do is they are one chapter, a very impressive chapter in that long argument, which brings together totally different kinds of evidence, all of which fits more or less. The fossil stuff has been, as I said, spectacularly increased in the last 10 or 15 years, and it fits.

And then the molecular stuff, which is now pouring out of the machines, also fits. But the modern stuff also fits. if you look at the adaptive, the way that whales have adapted to go beneath the water, we've heard a lot about flippers and so on. But when we look at the molecular genetics of the way they deal with oxygen shortage, the way they can deal with the... You get a stitch, you get lactic acid building up in your muscles,

if you exercise too hard. It doesn't worry them because they've got a new bichemical pathway. Another interesting thing which molecular genetics has come out with, which fits with the idea that you lose limbs if you're not using them, because it's expensive. Whales can't smell. They've got just the remnants of the smell system that we have. That's been lost because there are no smells under the ocean. So all these totally different kinds of data

suddenly come together on a harmonious tale. And what's more, Herman Melby wrote a book about it? Williamus, can you give us briefly, I'm sorry we're near the end of the programme, unfortunately, some idea of the size of the biggest whales and the diversity of these creatures? I think the diversity, when people, think of a whale. If you say what's your whale, people might think of a blue whale, which is

the largest organism. It has these amazing throat pleats. And it's also got the baleen, which it uses. And a lot of people will say, what do they, what whales feed on? They feed on plankton. In fact, the baleen whales are just one group of whales, and they do feed on not just plankton, but small fish, anything that they can scoop up in large quantities and sieve. But then the sperm whale of Herman Melville, Moby Dick, has these huge jaws, which it probably doesn't actually use for feeding. Feeds on squid at deep depths, and probably just sucks the squid in. But then we've got a whole range of dolphins, including highly specialised dolphins that live in rivers, fresh water, armed with very long snouts, almost blind with these batteries of tiny little needle-sharp teeth

ideal for catching fish in cloudy waters. We've got beaked whales, very poorly understood. their mouths, they probably can't even open their mouths in some species, are just formed into long tubes at the front, and they suck up squid rather like a child-eating spaghetti. So we've got a huge diversity of different... No, no, let me just panicking because we're coming towards you. Thank you very much.

Thanks, Bill Amos, Ellen Weston, and Steve Jones. Next week we'll be talking about St. Paul, and his influence on Christian ideas. If you've enjoyed this Radio 4 podcast, why not try others, such as Thinking Aloud, where Laurie Taylor discusses the latest social science research. To find out more, visit bbc.co.com.uk forward slash radio 4.