In Our Time - The Natural Order

Episode Date: April 6, 2000

Melvyn Bragg examines the science of taxonomy. The Argentinean author Jose Luis Borges illustrated the problematic nature of scientific classification when he quoted from an ancient Chinese Encyclopaedia, the Celestial Emporium of Benevolent Knowledge. On these remote pages, in a complete absence of Phylum, Genus and Species, animals are divided into: “(a) those that belong to the Emperor, (b) embalmed ones, (c) those that are trained, (d) suckling pigs” and “those that tremble as if they were mad” ending with “those drawn with a very fine camel's hair brush”, “others”, “those that have just broken the flower vase” and “those that at a distance resemble flies.”Perhaps our own system of classifying the natural world might seem just as fantastical to a more knowing mind, and perhaps underlying the Linnaean system that homo sapiens currently finds useful there are prejudices of our own which distort the scientific truth. How does natural history classify the ‘natural order’?With Colin Tudge, writer, scientist and author of The Variety of Life: A Survey and a Celebration of all the Creatures that Have Ever Lived; Dr Sandy Knapp, Research Botanist, Department of Botany, Natural History Museum, London; Henry Gee, Senior Editor of Nature and author of Deep Time: Cladistics, the Revolution in Evolution.

This BBC podcast is supported by ads outside the UK. 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, the Argentinian author Jose Louis-Borges illustrated the problematic nature of scientific classification when he quoted from an ancient Chinese encyclopedia,

the celestial emporium of benevolent knowledge. On these remote pages in a complete absence of phylum, genus and species Animals are divided into A, those that belong to the emperor, B, embalmed ones, C, those that are trained, D, suckling pigs, and those that tremble as if they were mad, ending with those drawn with a very fine camel's hairbrush, others, those that have broken the flower vows, and those that at a distance resemble flies.

Perhaps our own system of classifying the natural world might seem just as fantastical to a more knowing mind, and perhaps underlaying the Linnaean system that Homo sapiens currently finds useful, there are prejudices of our own which distort the scientific truth. With me to discuss how natural history classifies the natural order, the signs of taxonomy, is the science writer Colin Tudge, author of The Variety of Life, subtitled A Survey and Celebration of All the Creatures that have ever lived.

Dr. Sandy Knapp, a botanical taxonomist from the Natural History Museum, and we're also joined by Henry G, whose book Deep Time, Cladistics, The Revolution in Evolution, claims to subvert the status quo. Corintage, the Swedish nationalist Carl Linnaeus, is the great name in taxonomy. He's the one who gave us the formal structure for terms like Homo sapiens, for example. What climate was he writing in scientifically and what impacted his ideas have when he wrote his Systema Natura in 1753? Well, of course, he was bang in the middle of the Enlightenment, and there was a general idea that nature ought to be orderly, and it ought to be possible to discern what the natural order of nature was.

So he was very far removed from, as it were, the characters that you read out in Burgess, who were just, as it were, in an arbitrary and ad hoc fashion, just trying to get to grips with what's out there. But, of course, he was 100 years pre-Darwin, so he had no idea about evolution and really didn't think about it. And the pre-Darwinians, like Linnaeus, but the Enlightenment-type chaps, going back to the 17th century, actually, thought, because it seemed very reasonable,

that the order that should exist in nature, it's very much a should. First of all, should be like the kind of order that you see in the chemical elements where things are just generally similar to each other because, as it were, that's the way they are. They have innate properties that make them similar to each other. But secondly, which was a very important subtext, that whatever order was out there in nature must somehow reflect the orderly mind of God.

And there was a very strong idea, pre-Dalbidian idea, that in a sense the job of a scientist was to find out what God was thinking. Sandinap, would you explain, tell us how Linnaeus' system for the natural world is organized? How do his groups of classification interrelate? Well, I think that Linnaeus' system really was organized for utility, more than actually defining what he considered to be what we would call natural groups. Linnaeus, particularly in the plants,

which was where all of this binomial nomenclature of having a genus name and a species name, like homo sapiens. Can you extrapolate in that? Well, binomial, the scientific names of all living things essentially have two. parts, one of which is the genus, which is a sort of collective noun, which in which there exist a lot of species. Before Linnaeus... Like panthera Leo. Yeah, panthera Leo, homo sapiens, canis domesticus, Canis familiaris, I think it's called noun, canis lupus, the dog and the wolf. So pantheraio is the lion and pancerro Tigris is the jaguar. Yeah. Yeah. That sort of thing. So there's a couple of different

species in a genus and they're differentiated by various what we call characters, characteristics. Before Linnaeus, what she would have is long, what we call polynomom. phrases. So it would be, this was all science was done in Latin in those days. So this would all be in Latin, so I'll just say it in English just to make it easy. So you would have the large big cat with a mane that's kind of yellow and has a tail with a tuft.

And you would have the large big cat which is black and orange striped and doesn't have a tuft on its tail. And once you got to the point where you got lots and lots and lots of organisms, it became really difficult to find enough words to differentiate them all. And so what Linnaeus invented

was essentially a shorthand. that he would have the long polynomial with all the kind of descriptive adjectival type stuff in it. And then in the very margin of the book, and he invented this for plants and not for animals, he first used it for plants. He would have a one word that described what that sort of encapsulated that polynomial.

Henry G., can you tell us something about the underlying philosophy of Linnaeus system? What does it tell us about his perception of the state of nature? I think you have to think of a completely different mindset when you think of Linnaeus from the mindset with which we look at the natural world today, conditioned as we are by 150 years of Darwinian thought. Linnaeus thought of the world as a static system.

In other words, like the periodic table of the chemical elements, they don't evolve one into the other. They just are there and they have common properties that can be related to each other. Linnaeus classified minerals as well as animals and plants in the same system, and that wasn't seen to be very odd. But I think what Linnaeus and other natural historians were trying to do was trying to get to grips with the pattern of nature, which is like a tree.

It's a hierarchy. There are hierarchies of similarity. There are lots of species that are different. You know, they're cats with maines and tails and they're cats without, but they're all cats, and you can form a group. Similarly, there are dogs, and these are grouped together as carnivores, and they're grouped together and to mammals. So there's hierarchy of life,

which Linnaeus tried to summarize, but nobody sought to explain. It was just there, like the chemical elements, it was just the expression of the mind of God. It was only when Darwin came along. Darwin sought to find a mechanism that could generate a hierarchy. In other words, he saw the hierarchy and wondered how this could have come about.

Can you tell us the idea of a single perfect version? It could be clear we went back to Plato and even further back than Plato. Can you tell us about the archetype the way it figured in Linnaeus and why it's important? Yes, the archetype is the perfect expression of a species, an animal or plant, in the mind of God, the perfect cat. I'm rather fond of cats, so I'll talk about the perfect cat.

But it was different from the real cats we see around us. Real cats are varied, they're black and white ones and tabby ones and ginger ones, But these are just, these variations were just the imperfections of the real world, different from the imperishable spheres in which the archetype resided. So that in Linnaeus' time, there were very much two parts to natural history. There was the scruffy reality that you dealt with and the real idea of the archetype, the imperishable plan of the cat or dog. And what you were doing as a natural history was trying to get,

trying to see through all this messy variation to try and describe the essence of the archetype. And when Darwin came along, he said, this variation that you see in the real world isn't just an unfortunate consequence of mortality and reality. It's actually the stuff of evolution. And if you realise that, you have to get rid of archetypes. Sending up, I'm told that the Natural History Museum's collection contains an example of every plant and animal. species known. It's based of...

You've got 68 million, 68 million. 68 million is quite a lot. We don't have every single one. We have a lot of duplicates, so you have a lot of... Which again are the way you see variation. But it's based on something comes out of Linnaeus. Was the organisation of the museum founded along Linnaeus' ideas?

No, because the system was organised along Linnaean grounds in the beginning when Joseph Banks was a large contributor to the collections. But it's now organized along very different lines. We have five departments. So we have a department of botany where we keep the plants. We have a department of zoology where we keep the live animals, I mean the live dead animals, the embalmed ones in Borges's classification.

We have a paleontology department where we keep fossils, a mineralogy department where we have those minerals classified in Linnaeus' system, which is partly why minerals are at the Natural History Museum, and then we have an entomology department for insects. Is Linnaeus then, before we finally move away from him, Is Linnaeus, his views or his classifications, are they still currently useful at all in your work at the Natural History? No, we don't use them.

We don't use them at all. We do use Linnaeus' names, the names that Linnaeus coined for things like Homo sapiens or Asparagus Officinalis, the Asparagus, which is just coming into the supermarkets now. Those are the scientific names we still use. So Linnaeus' concept of what that name was and the material that he saw to give that plant or animal a name

are still very, very important to the correct application of names, to calling things the right name. But his ideas of classification we no longer use. Well, Darwin's been bursting to get into this conversation for the last five minutes, so let's let him in and start with you, Henry Jean. Come back to an idea of Darwin's idea of introduced the idea of evolution to the natural order, as everybody knows. Did this immediately banish Linnaeus' ideas, particularly, so, the archetype? Darwin and Linnaeus, I think, have had a very, they've been very, uneasy bedfellows for 150 years.

Evolution was in the air. It was kind of an enlightenment idea. Well, it actually goes back to the Greeks in various forms. Darwin's granddad, Erasmus, was very keen on this sort of thing. But Charles Robert Darwin, our hero, he first found a credible mechanism whereby evolution could have happened. People thought that species could have evolved into other species over time, but these were cocktail party chat kind of ideas.

They were scenarios, they were stories. But Darwin actually came up with a mechanism that could be tested and his mechanism of natural selection. But as Sandy says, we still use Linnaeus' names, but in a way we're trying to reconcile two irreconcilable systems. When Darwin came along, it was like saying, for the periodic table of the elements, that carbon could evolve out of high...

given certain circumstances. But if you look at the elements, you say, that's impossible, that just doesn't happen. You're frowning there, Colin. People can't, listening people can't see your frowning, but I can. I'm passing on the frown, and what's behind the frown? I just want to suggest that Linnaeus and Darwin are not as irreconcilable as all that. I mean, they do actually come from very different places. But whereas, you know, the idea of the species as an archetype is one kind of idea,

it's also true that we still have an idea of what a species is as being a pretty discreet. thing, i.e. it's a group of creatures which breed with each other but don't breed with anybody else. So it's still a discrete thing. Given that it's still a discrete thing, you can still give it a Linnaean type name very, very reasonably. And although it's got a different

philosophy behind it, it actually works reasonably well. I'm just personally uneasy about the modern definitions of species based on animals that reproduce with each other but not with other animals, because that's a processed-based

statement. How do you actually establish this? Okay, in the case of Panthera Leo, the lion, you can go to Africa and watch lions at it breeding with each other but not with other things. But firstly, it doesn't tell you about all lions. And the second is, if you work in a museum and you see the embalmed ones which come to your desk from all corners of the world, how do you know if they reproduced with each other or not? And if you have a museum, a fossil, you've got no way of finding this out at all. You have to go on what species look like. So I think this is where using processed-based notions like natural selection to impose order on your classifications comes very unstuck. And I think there are, you have to take a great deal on trust and faith to make it work.

Commentary, in origin of species the only diagram is of a tree. Do you think that there is still a combination of Linnaeus and Darwin which effectively answers the questions worth asking? Well, it is true, of course, that what Darwin did, the most important thing he did was to provide a plausible mechanism of evolution, i.e. natural selection. He also did something else which was actually different. And what he said was, not simply that species can change through time,

but that they can actually diverge so that one species could give rise not simply to another one that was its successor, but to several quite different successors, different lineages. Other people had said that you could start with primordial creatures, each of which changed separately, so you've got a series of separate ladders. Darwin was the first really to say that you started with a single ancestor

that then diverged into a huge tree. This is a quite different qualitative shift. So what Darwin was then able to say is that when you see groups of creatures that seem to be similar, so that, for example, you give them the same kind of name like panther, who put them in the same genus. It is not simply because that's the way God thought of it. It is because they are literally related with a common ancestor.

And in fact, not only do they, you know, cats have a common ancestor with other cats, they also have a common ancestor with dogs who live further back in time, and they had a common ancestor with some primitive reptile which lived even further back. And so on right the way back to the beginning, we would now say about 4 billion years ago,

4,000 million years ago to the first ancestor. Darwin didn't know it was that long, but right back in the past. So Darwin was the first person, person really to say convincingly all creatures on earth belong to the same tree, literally the tree, like an oak tree, and therefore you can base your classification on branches of this literal, what he said, genealogical tree. Henry G, in your book Deep Time, you said that natural selection is given too much weight as an agent of evolution,

and the Darwin's idea shouldn't be used to explain the relationship of species over immense stretches of time. Can you tell us more about that? First of all, I'll put my cards on the table. I am a card-carrying. Darwinian. I'm not here to be a creationist. However, I think in the process of classification you should try to be pragmatic. There is a tree of life,

and natural selection is a wonderful way of explaining how life comes to be a tree, for one thing. It would be inconceivable if natural selection has not played a major part in the origin of life. However, there is a problem. When you introduce notions of process of things happening

onto a tree, you imply certain things like cause and effect and ancestry and dissent, which it is impossible to see as a scientist from the present day. And this came to me when I was in the field, in Kenya, looking at fossils on the ground. And you can try this thought experiment. Pick up a fossil and say, how do I know this fossil is my ancestor? And you can't. A fossil is a fossil. It doesn't say anything.

A fossil is just a rock. the interpretation that we put on a fossil is only ours to make. In other words, we tell the stories. So the conventional picture that you had in museums until, say, 30 years ago, of stringing fossils in a line and drawing arrows between them and say, this speech is evolved into that one, and we can infer that one evolved from the other because of natural selection for certain attributes

is a total bedtime story. I would, if we weren't on the radio, I'd be much rude, about it than that. But it cannot be established. It cannot be tested scientifically. In other words, it rests only on the authority of who's telling it to you.

Can I come to cladistics now? Willie Henig, as a German entomologist of the 1960s, is the founder of this cladistics. You say in your book, Deep Time, quote, because cladistics describes a pattern rather than tells a linear narrative, it's uniquely suited to the study of deep time. Now, can you tell listeners,

because plodistics still is not widely known, although you think of it as a great revolutionary notion, what it is and why you think it's so very important? What Henig wanted to do was overturn all notions of arbitrary classification, like Borges is ones of animals useful to the emperor and all kinds of utilitarian ways. He wanted to work out the actual tree of life. He wanted to see the tree of life.

And if you're trying to look at the pattern of the tree of life, you must put away all kinds of clutter in your head about how that pattern might have been created by natural selection or by chance or by other things. But if I were to describe cladistics very simply, it's to look at the similarities and differences of living creatures in exactly the way a child might. Just see what's there

without any preconceptions of what ought to have happened. Now, what's happened after Darwin and in the media today, is we still think of evolution as progression. The conventional evolutionary stories see fossils as people and draw stories which have a human time frame. Colin Touch, Henry G. claims that cladistics is as bigger revolution as Darwin's theory, as greater breakthroughs.

Copernicus has discovered that the earth moves round the sun. Are we into hyperbole here, or would you pick that up? No, I think we're into hyperbole. It's a very important set of ideas. It's really a set of techniques that enables you not to make mistakes about what you think similar and what you think is different. And that in the end is what it is. But when Henry is speaking just then,

I hear the sound of, first of all, of straw men being attacked, and secondly of good babies being thrown out with the bathwater. I mean, to take the latter point, okay, one shouldn't, when you look at a group of fossils, assume that one is ancestral to another, because you just don't know that. However, you should never lose sight of the fact that one is supposing that there is still this tree of life,

in other words, that we all do have ancestors and that somewhere among those fossils, there are the ancestors. And if you tell the story in the kind of very purest way that Henry was giving us there where you're simply looking for patterns, you can lose sight of the idea that there really is an evolutionary tree in there somewhere.

And people who are not biologists, including the creationists, have actually, as a matter of historical fact, seized on the idea of these very purest ideas of the cladists to say, well, actually, there are biologists out there who are questioning whether evolution happened at all or whether there are descendants and ancestors at all.

So one should be rather purists, but if one overdoes it, then I think you throw out something very, very important. Sandy Nav wants to come in here. Well, as a practicing cladis, and a person who does this on a daily basis, is the real... You mean classifying plants.

But also I do it using the tools of cladistics. I use these tools all the time. And the really important thing, and I think the real breakthrough in cladistics, which makes it streets ahead of any other way of classifying things is repeatability. Because I can look at a set of organisms and I look at what we call their characters or their attributes.

Characteristics. So they're characteristics. So whether they have a little notch in the bone above their eye or, I'm much better at botanical examples. So say pink flowers, you would do your cladogram, you would do your tree of life, and these two things with pink flowers would come out as being related and you think, hmm, that seems a bit odd.

And so one of the really important things that Henig invented as well is that you go back and look at these characters again. You don't come up with your hypothesis of what the tree of life is and then say, right, that's it, we'll move on and go do kind of mechanical engineering now. You go back and look at that. And so in my pink flower classification, for example, you would have two things that have pink flowers and you'd look at them and you think, no, wait a minute, there's lots of other things, characteristics which these don't share. I wonder if I should look at that character pink flowers again. And you go in and look at it, and say your two pink-flowered things are a rose and a cactus, because

you know, cacti often have those bright, beautiful pink flowers. And it turns out that the chemical that makes pink is different in those two things. So that means that pink flowers aren't what we call homologous, so pinkness isn't the same thing. And so actually, Cladistics allows us to go back and repeat things and learn more and more about how the world is made up. Can I touch, Henry G. claims that you can never really scientifically know whether one species as the ancestor of another. Do you agree before I come to turn to Henry himself? No, that has to be true. I mean, a very good example is archaeopteryx, which may or may not be the first bird. I think everybody agrees that this pile of old rock that people found is a fossil, and furthermore, it's a fossil creature which looks very like a bird.

When it was first discovered in the 19th century, people said, well, this half like a fossil and half like a generalized reptile. Therefore, it is the ancestor of birds. Now, that, of course, is a huge assumption when you think about it, that this one fossil that you found out of the millions of creatures that must have been living, must be the ancestor of all modern birds. So what the cladist said was, no, no, no. We can say that this is probably related to the very first bird. It looks like what we imagined the first bird was like. We can represent it as a relative.

We simply cannot honestly represent it as the ancestor. I mean, that's the unscientific bit. Birds are a good one to pause for thought for a moment with Henry, because what would the Darwinian, common Darwinian notion of the evolution of the bird be, and what would it be the cladistic gloss or subversion of it? The common idea of the origin of birds makes a wonderful story.

It is that there were little lizard-like things, not lizards, but little small reptiles living in trees, that jumped from tree to tree or jumped around, and the more they jumped, the more that adaptations for staying in the air longer became selected for. This is easy to see if a lizard landed on the ground, splat and got eaten, it obviously wouldn't leave many descendants. So as millions of years came

along, there were feathers and wings and lo and behold, we have a bird. Now, of course, that's a tiny caricature of this idea, but essentially it's basically the idea of explaining the pattern of evolution, in other words, the existence of a group of creatures we call birds, in terms of a process, natural selection. But when you think about that, why must that be so? Why should it be that the origin of birds and the origin of, say, flight, their major characteristic, go together. There is a logical flaw in here somewhere. If you take the exemplar of flight, the feather,

now we see that all birds that we see today have feathers, and we use that as a characteristic of the bird. But just because all birds have feathers, does that mean that all feathered animals that ever might have existed must have been birds? That's like saying that if all elephants have four legs, then all four-legged animals must be elephants. And this wonderful idea is easily punctured by the discovery of other animals,

which are clearly not birds, that have feathers and other adaptations for which we would see as adaptations for flight, but in animals that were patently non-flying. That completely destroys your human-centered notion, the my descendants will write the book notion that you can look back at the fossil record and tell what went on. Colin Judge, what's your reaction to that?

I think Henry's over-telling the story. I mean, the point is that something happened in the past and the whole job of science is to find out what deed, and it must be the case, it really must be the case, that flying animals evolve from non-flying animals. We know that non-flying animals existed first. It's perfectly true that you can find dinosaurs these days that had feathers and didn't fly,

so you say, well, feathers preceded flight. But the point is you have to, at some point, impose some scenario as to what happened in the past. Otherwise, what's the point of science? Otherwise, you've just got a pile of rocks. Now, one might start with a rather primitive story that lizard jumped about in the trees and they stayed in the air longer.

Then you expand that into a bigger story of other possibilities. But the first story is an heuristic device. It isn't simply human beings trying to, you know, tell their own story, imposing a certain nature. I think that as the past, of things becomes clearer and clearer because this story of lizards kind of jumping around in trees and then evolving into archaeopteryx into birds, our kind of linear progression, is the sort of thing that people talked about quite a long time ago before many of these fossils with feathers that

didn't fly or before a lot of information. And one came to light. And one of the things that's exciting about doing systematics is that there's always something new. People are always finding yet another fossil or another new species of organism in the Amazonian rainforest. and we by no means know everything yet. A huge percentage of what was out there and what is out there is left to be discovered. And I think as we refine that pattern, then our heuristic device becomes different.

And there's nothing so bad in that, I think, is changing the story, because the story isn't the hypothesis. The pattern is the hypothesis. Is there a worry that new systems of taxonomy might challenge common sense? There's a lumping together of the lumpfish with the cow rather than the lumpfish with the salmon?

Common sense is there to be challenged. Our ideas of common sense depend on our very subjective, parochial human experience. So I take the issue with Colin. We cannot impose scenarios on the past. It's not scientific, and I think Colin is afraid by saying that if we don't use evolution to tell a story, the creationists will jump on us.

Well, I think we've got to be honest. I think the creationists are wrong because they are scientifically flawed, but we must be honest as scientists and tell it like it was, and how we want it to be. Well, we seem to be having an argument about what science is really for, because I think science is really about trying to find out what really happens out there in the universe. It really is an interesting question, what did happen in the past, something happened in the past.

Actually, the only way that human beings can find out what happened in the past is by imposing stories and then asking whether those stories are true. Henry is now telling us that you cannot do this. Now, that is actually foolish. It's not the case. That is actually what you have to do. Well, I think just to tell stories and base them on authority is not just unsartific. I think it's dishonest. However, there is a middle ground to be struck.

When you come up with your picture of the pattern of the tree of life, just based in a way a child would look at it, just on the characteristics that are there, you can then test your ideas of process of what might have happened and find out which ones are more likely. than others. Now, it now seems very likely that birds share a close relationship with dinosaurs and the things that we see we thought of as adaptations to flight were adaptations for other things entirely because they evolved before flight did. But where I do take issue is where people

try to impose some function on these things. When the feathered dinosaurs were discovered, people phoned me up and said, if feathers weren't evolved for flight, what were they evolved for? And I said, haven't you learned the lesson here? How do we know? They could have been involved for tickling each other to death for all we know.

Do you want to judge between these two? No, you don't. I actually think that probably the majority of practicing taxonomists, those of us who sit in the corridors of the Natural History Museum, fall in that middle ground. Thank you very much. Thanks, Colin Tudge. Thanks also for the best subtitle I've ever heard,

a survey and celebration of what creatures have ever lived. Deep time isn't about either, Henry G. Thank you very much, Sunday, up. Back to National History Museum. Thank you for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programs about history, science and philosophy at BBC.com.uk forward slash radio 4.