Aristotle's Lagoon


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Aristotle's Lagoon

Professor Armand Leroi visits the Greek island of Lesvos to discover the creatures, places and ideas that inspired Aristotle during his pioneering work in the science of biology.


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There is, in old Athens, a bookshop.

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It is the loveliest one I know. I discovered it 10 years ago

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and within it I found something wonderful.

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There, on a shelf, was a series of volumes,

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the collected, translated, works of Aristotle.

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Impressive, certainly.

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But I wasn't much interested.

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Philosophers and poets and playwrights may all worship

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at the shrine of Aristotle, but not scientists.

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And then I opened one.

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The book was called Historia Animalium,

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The Natural History of Animals.

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It told of snakes, sharks, and sea urchins, how they are built,

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where they live and what they do there.

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Assertion followed assertion, fact followed fact, like hammer blows.

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It was long, it was dense, it was impenetrable.

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And yet, it was magnificent.

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Aristotle, the man who gave us logic, poetics, political philosophy

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had also known, loved and sought to understand the natural world.

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Working by a lagoon on a Greek island, he investigated,

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analysed and documented the world of animals and plants.

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And did so in a wholly new way.

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There he discovered order in the chaos of organic diversity

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and there he invented a science.

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And though it was my science, biology, I did not know it.

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But then, hardly anyone does.

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For Aristotle's biology, strange, difficult and yet wondrous,

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is almost completely forgotten.

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In the 10 years since I found that book in an Athens bookshop,

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I've been living with Aristotle,

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trying to understand the workings of his astonishing mind.

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What did he do?

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Why did he do it? And how?

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And, most of all, why have we forgotten him,

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the first, and perhaps the greatest, biologist ever?

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The Scottish zoologist,

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D'Arcy Thompson, who translated Historia Animalium, wrote that

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the lagoon where Aristotle worked was on the Aegean island of Lesvos.

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That same day, I boarded the evening ferry from Piraeus.

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It's 347 BC and Aristotle is fed up.

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For 20 years he has been at Plato's Academy,

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first as a student, then as teacher.

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But now Plato is dead and there's vacancy at the top.

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Who should be the new head of the Academy?

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"Well", thinks Aristotle, "obviously it should be me."

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Intellectually voracious,

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in the philosophical hothouse, he's the best.

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Plato calls him The Reader.

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And he's original. Perhaps excessively so.

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In the event, the job goes to Plato's nephew.

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"Very well", thinks Aristotle.

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"I'll pack my bags and go where I'm appreciated."

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And off he goes.

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East, across the Aegean.

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GREEK STYLE MUSIC

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In the years that I have been searching for Aristotle,

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I have come to know and love this island.

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My dearest friend here is Giorgos Kokkoris,

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an ecologist at the University of the Aegean, Mytilini.

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It was he who first took me to the lagoon.

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And it is he who takes me there now.

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It was on the shores of this calm lagoon that, 23 centuries ago,

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Aristotle did so much of his ground-breaking biology.

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He knew it as Pyrrha.

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Today they call it Kalloni.

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But, for me, it is "Aristotle's Lagoon".

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Lesvos is the perfect place for a naturalist.

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In no other Greek island

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is the natural world so endlessly present and richly seductive.

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On the frontier of Europe and Asia,

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Lesvos draws its creatures from both.

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In spring and autumn, it is a resting place for millions of birds

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migrating between Africa and the north.

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What do we see over there?

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There are avocets.

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Filios Akriotis, Greece's leading ornithologist, lives on the island.

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He takes me for an Aristotelian walk

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in the marshes and woods that flank the lagoon.

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For me, science is an endless conversation about the world.

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Was it so for Aristotle?

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He came here to Lesvos

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at the invitation of a friend, Theophrastus.

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-At least, that's what many scholars believe.

-Yeah.

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But who exactly was Theophrastus and what did he do?

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He was a botanist, I gather.

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Theophrastus was a botanist.

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He was another very special person of those times

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who has given us written descriptions

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of a very big variety of plants.

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Actually, many of the plants of today are named after Theophrastus,

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have their scientific names based on his name.

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Quite a remarkable person.

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One imagines the two men, friends, dividing up the natural world.

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"I'll do the animals", says Aristotle.

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"You, Theophrastus, do the plants".

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And so zoology and botany were born.

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Aristotle describes the forms, habits and habitats

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of hundreds of animals.

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He says that tortoises have shells, hiss, lay eggs and hibernate.

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That snakes copulate by entwining themselves.

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He describes the life cycle of the cicada.

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He tells of a bird with steel blue plumage, a long and slender beak,

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short legs that lives on rocks, obviously a rock nuthatch.

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He turns his attention to the water's edge.

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"In the shallows", he says,

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"the vegetation is more delicate and lush than any garden.

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"There is a kind of crab that has flattened hind limbs

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"with which it swims".

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He says that ibises, herons and egrets

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use their beaks as fishing spears.

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And that stilts are very quarrelsome and do not have a hind toe.

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And he describes the loveliest of the spring migrants,

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the European bee-eater.

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Aristotle notes their voracious appetite for bees, how they nest

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in holes that they dig in riverbanks and how they breed.

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And so, each year by the Lagoon,

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the bee-eaters still do.

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This is the philosopher discovering nature.

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He was not prejudiced by anything.

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He was not influenced by somebody who wrote about the same thing

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some time ago and had read about it when he was young.

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Yes, a freshness. That's what I admire in his writing.

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Everything he writes seems to be his own observations.

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In a wonderful passage known as the Invitation to Biology he says,

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"It's not good enough simply to study the stars,

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"no matter how perfect and divine they may be.

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"Rather we must also study the humblest creatures,

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"even if they seem repugnant to us.

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"And that is because all animals have something of the good,

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"something of the divine, something of the beautiful".

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But make no mistake,

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Aristotle is no mere naturalist.

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He collects facts, lots of facts, and arranges them.

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He's systematic, relentlessly so.

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He classifies.

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In Historia Animalium alone,

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he names and distinguishes 110 kinds of animals.

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And he's especially good on fish.

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Oh, nice.

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What is this beautiful thing?

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-Melanis.

-Melanis. Melania.

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-Tsipouris.

-Tsipouris.

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So, right here, we have about seven, eight, nine species of fish

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and they're all the fish that Aristotle describes.

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And he does so in wonderful detail.

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He talks about their forms and their proportions,

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where they live and how they breed and how they come into the lagoon,

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in and out every year.

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But Aristotle also notices that some species resemble each other.

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Aristotle classifies many of the creatures he finds in the lagoon

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into larger groups and you can see them here.

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Such as these things which I am trying to get.

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Which are sea squirts.

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He puts "sea squirts", so called because they squirt,

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and snails and sea urchins all in the same group, the ostracoderma,

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because they all have rather hard exteriors.

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He puts crabs, which also have hard exteriors,

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into a different group because they have legs.

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It's the beginning of the great classifications that we know today.

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Not all of his classifications have stood the test of time.

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Sea squirts, snails and sea-urchins are, in fact,

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quite unrelated to each other.

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But the 19th Century discovered that.

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And he's superb on dolphins.

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Aristotle notices that although dolphins live in water

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and look a bit like fish, they breathe air and suckle their young

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just as many land quadrupeds do.

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He therefore puts whales and dolphins, cetaceans,

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in a group of their own.

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His successors ignored him and just called them fish.

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What makes a scientist turn to the study of the natural world?

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So often, it is a place.

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And whatever that place is, it stays with him for the rest of his life,

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for it is where he first sees the beauty and delight of living things,

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begins to understand their mysterious order and glorious

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confusion and it is where he first begins to wonder why.

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And that is Aristotle's question.

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For he's in search of the deepest causes of things.

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And to do that, he knows that he can't simply go about

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pressing wild flowers and check listing birds.

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He has to get into the guts of things.

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But to do that, Aristotle first had to find a friendly fisherman.

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-Hey, Dimitri.

-Hi, Armando.

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-Kalimera.

-Kalimera.

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So what do you say? Let's do some fishing.

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Historia Animalium

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is so filled with observations about the creatures that live

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in and around the lagoon that they cannot all be Aristotle's own.

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He must have interrogated people who knew about animals.

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As Darwin wrote to pigeon fanciers, so Aristotle spoke to fishermen.

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So roughly where are we going? Are we going over there to the right?

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That direction. About in the middle. About in the middle.

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About half way down the lagoon.

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-Yeah.

-The lagoon cuts the island of Lesvos nearly in two.

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It is one of the most productive stretches of water

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in the Eastern Aegean.

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And it contains an animal to which Aristotle was particularly devoted,

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the cuttlefish.

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The first few traps are empty.

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But there are cuttlefish down there.

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These are the eggs.

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Yeah.

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The net's just covered in them.

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-Exactly.

-That's fantastic.

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God, there must be thousands and thousands of cuttlefish down there.

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You can see the embryo. Look.

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-Yeah.

-You can see the embryo!

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I didn't expect that.

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I thought they stayed black all along, throughout their development.

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No, some of them, they haven't been sprayed.

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-Not all of them. Very few.

-You mean they haven't been fertilised?

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Yeah. No, no, they have. But they are, usually when they are finished,

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-they spray with the ink to protect.

-Oh, I see. I see.

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The ink is the last thing they do.

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But, the pale ones, you can see right inside them.

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And you can see the little baby cuttlefish.

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-Yeah, they're moving.

-And they're moving, you're absolutely right.

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You can see its eyes. You can see exactly as Aristotle describes it.

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My god, they're gorgeous. They're amazing.

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In a week or two, they all will be gone.

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And then we see movement,

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cuttlefish, dozens of them.

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These weird, wonderful animals infest the lagoon

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and Aristotle has a lot to say about them.

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He describes how they change colour

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and how they eject ink when they're afraid.

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How they breed. How they hunt with these amazing long tentacles.

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And the fact that they only live for about a year.

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One of Aristotle's masterpieces is the dissection of the cuttlefish.

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Aristotle describes the anatomy of a cuttlefish in detail.

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He describes its gills over here,

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he describes its reproductive organs. This is a female.

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These are the glands with which it produces the shell.

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He knows that cuttlefish have a very unusual anatomy insofar that

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the guts are bent around such that, in effect, it defecates on its head.

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Its rectum is located very close to its brain and its eyes,

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underneath the mantle cavity, unlike most creatures whose rectums

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are at the opposite ends of their bodies from their mouths.

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The mouth, the beak,

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which is hard, with which it bites,

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over there.

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He looks inside of the cuttlefish and he sees that the biggest organ

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is a big orange thing, which he calls the mytis.

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And it's right in the middle of the body.

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He thinks that this is the heart

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or at least the equivalent of a cuttlefish heart.

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It isn't. It's the liver. But because it's centrally located

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and our hearts are centrally located, he, in effect,

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argues that they are the same thing.

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It's an easy mistake to make. And it must be said that

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everything else he does is just incredibly impressive.

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Aristotle's description of the anatomy of the cuttlefish

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was not bettered until the 17th Century when a Dutchman,

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Jan Swammerdam, found the cuttlefish's hearts,

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all three of them.

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You might expect that a book like this would be ordered by species,

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that there would be a chapter on insects and another chapter

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on the cuttlefish and lizards and so on and so forth.

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But it isn't. In fact, it's ordered by system.

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There are sections on digestion and reproduction and life cycles.

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Really, it's ordered like any modern invertebrate zoology textbook.

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And it's that that tells us that Aristotle

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isn't simply accumulating natural history knowledge.

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He's doing something much more systematic.

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He's doing science.

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And therein lies a paradox.

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The way in which Aristotle structured this book

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is so familiar to us, so very much a part of the way we think about

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the natural world and how we do biology, that it's almost impossible

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for us to understand just how original he was.

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And yet, when he came down to this lagoon,

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saw the creatures in it, cut them up and wrote down what he saw,

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he was the very first person to have ever done so.

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What he does next is revolutionary. Having sorted his data,

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having arranged his facts, he begins to explain.

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He pits theory against observation.

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He invents a new way of understanding the world.

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A COCK CROWS

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He applies this method to one of biology's deepest problems...

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..how life originates in the egg and in the womb.

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He wants to know how, the words are his, living things "come to be".

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If you really want to understand development,

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you have to do what Aristotle did.

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You have to go to a farmyard

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and get yourself some fertilised chicken eggs.

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One of the charms of this is that you just don't know

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what you are actually going to see until you open the egg.

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Sometimes, when you do,

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you see exactly what Aristotle saw.

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Aristotle would have looked inside the egg with the naked eye.

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But we can do a bit better with this handy microscope,

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which attaches to my computer. It's a little bit tricky,

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but if you focus it just right...

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..you can see what I'm seeing.

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It's an embryo, not more than a few days old, lying there, minute,

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on its bed of albumen and yolk. With the blood vessels,

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the vitelline arteries and veins ramifying into its surroundings.

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You can see its head.

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You can see its eye.

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And above all, you can see its little heart, just beating there.

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Even Aristotle's detractors, and he does have them,

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have to give him credit for this.

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He's the first person to open an egg and describe the embryo of a chick.

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He's the first person to describe the origin of a living thing.

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Aristotle describes the growth of an apparently inanimate egg

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into a living, breathing, copulating creature.

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Had he done just this,

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he would be worthy of our admiration.

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But I think he did much more.

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I think he attempted to, and largely succeeded in,

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penetrating to the very deepest secrets of life.

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Why do chicks hatch from chicken eggs?

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Why not tortoises, fish or snakes?

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It sounds like a trivial question, but it isn't.

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It's a question about why progeny look like their parents.

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It's a question about inheritance.

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Aristotle argued that the properties of matter, the elemental building

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blocks of the world, cannot explain how an embryo constructs itself.

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Something else is needed.

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Something that it gets from its parents, something that shapes it.

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And he called that thing eidos.

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Which is what, exactly?

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Well, this is where Aristotle gets hard.

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This is where he we hit his metaphysics.

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We need a classical philosopher.

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This is what one looks like.

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Richard King and I have been talking Aristotle for years.

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Aristotle takes a comparison between

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the material constituents of things, the elements, as he calls them,

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and the form or eidos. And he says,

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"The elements are like letters A and B and you can combine

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"them in various ways.

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"So you can either have the syllable AB or the syllable BA,

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"AB or BA, and the arrangement,

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"well, that's the form and the form is different in each case.

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"So the form is different from the material constituents".

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So what he seems to be saying is that it's not the stuff of which

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it's made that matters, it's the way in which that stuff is ordered.

0:26:200:26:24

Exactly, exactly. It's the order of the material constituents

0:26:240:26:29

just as the order of the letters makes the two different syllables.

0:26:290:26:33

So what eidos really is is something like information?

0:26:330:26:37

That's right. Information or a kind of activity.

0:26:370:26:42

And the really remarkable thing is,

0:26:420:26:45

he's using a metaphor for information,

0:26:450:26:49

the order of the letters that is almost exactly like the metaphor

0:26:490:26:53

that we use when we speak about the genetic code, about DNA.

0:26:530:26:57

After all, it's not the material constituents of DNA that matter,

0:26:570:27:01

rather it's the order of the elements of which DNA is made up,

0:27:010:27:04

the molecules, the nucleotides, that's the information.

0:27:040:27:08

That's right.

0:27:080:27:09

One of Aristotle's methods for studying living things

0:27:170:27:20

was simplicity itself. He cut them open while still alive.

0:27:200:27:26

Aristotle has an enthusiasm for vivisection

0:27:320:27:37

that today seems excessive.

0:27:370:27:40

He describes how, if you cut an insect such as this in half,

0:27:400:27:45

it lives for a surprisingly long time.

0:27:450:27:47

Well, lots of modern biologists vivisect insects.

0:27:570:28:01

But few vivisect chameleons.

0:28:010:28:03

Aristotle did.

0:28:030:28:06

"After being cut open", he observes,

0:28:060:28:08

"the chameleon continues to breathe for a considerable time."

0:28:080:28:13

And tortoises. "They", he says, "continue to wiggle their legs

0:28:160:28:21

"even after their hearts have been removed."

0:28:210:28:23

I don't know how long a tortoise would survive without its heart.

0:28:250:28:30

And I am not, I think, inclined to find out.

0:28:300:28:33

And yet Aristotle's belief that some creatures can survive

0:28:330:28:37

for a surprisingly long time when eviscerated strikes

0:28:370:28:40

to one of the deepest parts of his research programme.

0:28:400:28:43

For when Aristotle cut out the heart of a tortoise,

0:28:430:28:48

he was in search of nothing less

0:28:480:28:53

than its soul.

0:28:530:28:54

The ancient Greeks allegorised the soul as butterfly.

0:29:060:29:11

They used the same name for both, psyche. It's easy to see why.

0:29:110:29:16

The butterfly clambers from the dark chrysalis just as the soul,

0:29:220:29:27

immaterial and immortal, flees a corpse at death,

0:29:270:29:30

yet lives on in Hades. It's the soul as spirit.

0:29:300:29:35

Aristotle's view of the soul is very different.

0:29:400:29:43

He thinks that all living creatures, not just humans, have one.

0:29:430:29:49

He thinks that mussels and clams and lobsters and crabs all have souls.

0:29:490:29:54

Or at least they did when they were alive.

0:29:540:29:58

For, Aristotle thinks, when a living thing dies, its soul dies with it.

0:29:580:30:04

This is the soul as biology.

0:30:090:30:13

Yet when you read Aristotle on the soul, it seems rather mysterious.

0:30:130:30:17

It's not material, yet it controls matter.

0:30:170:30:21

It's not an organ that you can dissect out and hold in your hand.

0:30:210:30:25

It's something much more abstract.

0:30:250:30:29

The soul is the network of command and control that makes a creature.

0:30:300:30:35

It's the flow of nutrients throughout its body,

0:30:350:30:39

it's the workings of its organs,

0:30:390:30:41

it's the senses with which it perceives the world.

0:30:410:30:44

And in the case of a man, it's the thoughts he thinks.

0:30:440:30:49

It is what 21st century biologists simply call The System.

0:30:560:31:01

It is a creature's metabolism

0:31:030:31:05

and the circuitry of genes and proteins that control it.

0:31:050:31:08

It is all the devices that stave off entropy and stop living things

0:31:110:31:17

collapsing into heaps of inert matter.

0:31:170:31:20

What Aristotle calls the soul, we call the system.

0:31:230:31:27

What he calls eidos, we call genes.

0:31:270:31:30

The language is very different but the concepts are much alike.

0:31:300:31:34

At the heart of both theories of life

0:31:340:31:36

is the idea that information handed down from parent to child,

0:31:360:31:40

generation upon generation, shapes living matter.

0:31:400:31:45

Aristotle believes that every species has a unique eidos,

0:31:490:31:54

its own particular soul.

0:31:540:31:56

Why, then, are there so many species?

0:31:570:32:01

For us, there are two explanations,

0:32:010:32:04

a religious one, God made them, and a scientific one, they evolved.

0:32:040:32:10

Aristotle has a relentlessly scientific mind,

0:32:180:32:22

but he lived 23 centuries before Darwin.

0:32:220:32:24

So is he a creationist?

0:32:240:32:27

His teacher Plato certainly was.

0:32:270:32:30

Plato gives an account of the origin of animals,

0:32:320:32:35

and it's a frank Creationist myth with a moralising twist.

0:32:350:32:40

God made the cosmos and then,

0:32:400:32:42

as punishment for various misdemeanours,

0:32:420:32:45

turned some humans into animals. The frivolous became birds,

0:32:450:32:49

the low-minded became lizards, snakes and things that crawl.

0:32:490:32:53

Others became fish.

0:32:530:32:56

Only the sober-minded remained human.

0:32:560:32:59

Aristotle thinks all of this is nonsense.

0:32:590:33:03

He has no time for creation myths, all that talk of the ancient Gods.

0:33:030:33:07

"I love Plato", he said, "but I love truth even more".

0:33:070:33:12

So is he an evolutionist?

0:33:150:33:19

He has Darwin's sense of how creatures are fitted to

0:33:190:33:22

the environments in which they live.

0:33:220:33:24

He describes how the beaks of birds are suited to their food.

0:33:260:33:30

"Creatures are", he says, "designed to survive and reproduce".

0:33:300:33:36

And, he's quite clear,

0:33:360:33:37

there isn't a celestial designer.

0:33:370:33:41

Nature designs living things and does so beautifully.

0:33:410:33:48

He thinks that some animals are more advanced than others.

0:33:560:34:02

There is a scale of complexity.

0:34:020:34:05

Most remarkably, he tells us that apes are intermediate in form

0:34:080:34:12

between quadrupeds and humans, which is certainly true.

0:34:120:34:16

It all sounds terribly Darwinian.

0:34:180:34:21

But it isn't.

0:34:210:34:22

For Aristotle isn't an evolutionist.

0:34:220:34:24

He's something much stranger.

0:34:240:34:27

Aristotle thinks that the world

0:34:300:34:32

that we see before us has simply always been there, unchanging.

0:34:320:34:37

He is, in other words, an eternalist.

0:34:370:34:41

It's a difficult idea to understand.

0:34:430:34:46

Our conceptual world is constructed on a Manichean conflict

0:34:460:34:50

between Creation and Evolution and Eternity simply isn't an option.

0:34:500:34:55

Eternity denies history.

0:34:550:34:59

It says that the past is not a very different place,

0:34:590:35:04

but the same place forever and forever and forever.

0:35:040:35:10

Which brings us to one of the most puzzling gaps in his science,

0:35:120:35:17

the fact that he doesn't say anything about fossils.

0:35:170:35:21

It's hard to see how Aristotle missed this.

0:35:240:35:27

We're on the western end of the island amid the remains

0:35:270:35:32

of a vast forest, but the trees are now stone.

0:35:320:35:36

It is one of the world's great petrified forests.

0:35:360:35:41

Some people say that theory blinkers scientists.

0:35:460:35:51

I don't think that's true, at least not in any strong sense.

0:35:510:35:56

And yet,

0:35:560:35:58

if you don't believe that the past is a different place,

0:35:580:36:01

it's easy to see how you could mistake a forest

0:36:010:36:05

for a field of stones.

0:36:050:36:07

An ancient volcano covered them in ash.

0:36:090:36:12

Now, 20 million years later,

0:36:120:36:13

you can still see their leaves, bark and tissues.

0:36:130:36:17

Aristotle's friend, Theophrastus,

0:36:200:36:23

the founder of botany, lived just a few kilometres away in Erissos.

0:36:230:36:28

Did he see them?

0:36:280:36:30

I asked Nicholas Zouros,

0:36:320:36:34

the Director of the Lesvos Petrified Forest, about it.

0:36:340:36:38

We know that Theophrastus was born just next to Erissos

0:36:400:36:44

and I am sure that once he visited this site.

0:36:440:36:49

So, for me, it is quite obvious

0:36:490:36:52

that he would have seen these silicified trees.

0:36:520:36:57

For me, it's absolutely unbelievable that a person like Aristotle,

0:36:570:37:03

or like Theophrastus, have not seen this.

0:37:030:37:08

Perhaps he just missed the entire forest.

0:37:120:37:15

Perhaps it was covered up.

0:37:150:37:17

But I suspect that the real reason Aristotle doesn't mention this

0:37:170:37:22

or any other fossil is not because he didn't see them,

0:37:220:37:25

but because he didn't believe in them.

0:37:250:37:28

Still, the question remains.

0:37:370:37:41

If species weren't created and did not evolve,

0:37:410:37:44

why then are there so many of them?

0:37:440:37:48

Aristotle understands that species

0:37:480:37:51

are connected to each other in very complex ways.

0:37:510:37:54

He compares the world to a house,

0:37:540:37:56

the Greek is oikos, from which we get our "ecology".

0:37:560:38:00

And in the household of the world, every species has its own role.

0:38:000:38:07

Aristotle knows that households are not always harmonious.

0:38:120:38:17

He understands, as Darwin would, that there is a war of nature.

0:38:170:38:22

But where in Darwinian wars some species flourish while others

0:38:220:38:27

go extinct, in Aristotelian wars the combatants simply fight forever.

0:38:270:38:34

But earthly creatures are not the only inhabitants of

0:38:460:38:49

Aristotle's household, the sun, the planets and the stars are as well.

0:38:490:38:54

His ecology embraces the cosmos.

0:38:570:39:00

And regulating it all is God, a God who simply thinks.

0:39:000:39:06

And though his God is the ultimate, remote intellectual,

0:39:060:39:11

he is also the reason for life on earth.

0:39:110:39:15

It's a beautiful, if slightly mystical, doctrine.

0:39:180:39:23

For it says that the nature that Aristotle described,

0:39:230:39:26

dissected and classified is, in fact, sacred.

0:39:260:39:30

Had I a God...

0:39:340:39:36

HAD I a God,

0:39:360:39:38

he would surely be Aristotle's.

0:39:380:39:41

Aristotle's world is very different from ours.

0:39:500:39:54

Our world does have a history,

0:39:540:39:57

one that can be seen in this very lagoon.

0:39:570:40:01

Had Aristotle ever sat at this spot,

0:40:080:40:11

he wouldn't have been by the water's edge.

0:40:110:40:14

That's because tectonic movements

0:40:140:40:16

have been shifting the islands beneath the Aegean.

0:40:160:40:20

And for millions of years the shoreline has been rising.

0:40:200:40:24

The ecology of the lagoon has changed, too.

0:40:290:40:33

The most enchanting creatures that live here are surely the flamingos.

0:40:330:40:39

For all their flamboyance, Aristotle does not mention them at all.

0:40:390:40:45

They are newcomers and only arrived here a few decades ago.

0:40:470:40:50

Other changes to the lagoon's ecology are more disturbing.

0:40:550:40:59

Giorgos Kokkoris and his colleagues from the University of the Aegean

0:41:040:41:08

have been monitoring the lagoon. They have found that pollution

0:41:080:41:12

and over fishing are taking their toll on its creatures.

0:41:120:41:15

I asked him about the lagoon's future.

0:41:150:41:18

The problems that we have faced

0:41:200:41:22

in this lagoon, these are the problems that we face

0:41:220:41:27

in the entire Aegean. And actually, in the entire world, I would say.

0:41:270:41:32

Biodiversity is threatened, fish catches have lowered.

0:41:320:41:37

I think the situation will deteriorate and some day

0:41:370:41:41

the fishermen will come and say that

0:41:410:41:44

there is nothing else to fish down there.

0:41:440:41:48

You know,

0:41:480:41:50

I know that what's happening here is happening right across the Aegean

0:41:500:41:55

-and the world.

-It is.

0:41:550:41:57

And as such, the lagoon is really just a microcosm

0:41:590:42:04

of that larger picture of ecological devastation.

0:42:040:42:10

And yet, for me,

0:42:100:42:13

the fact that Aristotle worked here and that this

0:42:130:42:17

is where biology began,

0:42:170:42:19

makes the destruction of this lagoon a thing of unutterable sadness.

0:42:190:42:26

If this lovely lagoon inspired Aristotle's vision

0:42:270:42:31

of an eternal and harmonious world, then there is bitter irony

0:42:310:42:37

in the fact that history has now caught up with it.

0:42:370:42:41

GREEK STYLE MUSIC

0:42:410:42:47

Aristotle continued the work that he began on Lesvos.

0:42:550:42:58

He wrote books about the anatomy,

0:42:580:43:00

physiology and development of animals.

0:43:000:43:03

There is a book about breathing,

0:43:030:43:05

another on ageing, another on movement.

0:43:050:43:08

There is a book on the soul.

0:43:080:43:11

The scientific legacy he left is not vast,

0:43:110:43:15

it is monumental.

0:43:150:43:17

It was read, copied and plagiarised by Roman encyclopaedists,

0:43:200:43:26

Muslim physicians and Medieval scribes.

0:43:260:43:28

By the 13th century

0:43:280:43:30

it was being taught throughout the universities of Europe.

0:43:300:43:36

In the Renaissance, scholars rearranged his books

0:43:400:43:43

into catalogues with exquisite illustrations

0:43:430:43:47

depicting the creatures that Aristotle had seen.

0:43:470:43:51

They founded museums full of natural wonders,

0:43:550:43:58

not unlike this one in a small village near the lagoon.

0:43:580:44:01

In fact, it's no exaggeration to say

0:44:040:44:07

that modern biology was founded on Aristotle.

0:44:070:44:11

Which raises the question,

0:44:150:44:18

why have we forgotten him?

0:44:180:44:20

Why has he no place in the pantheon of great scientists next to, say,

0:44:200:44:27

Pasteur or Darwin?

0:44:270:44:29

One reason is that some of his biology was, very simply, wrong.

0:44:310:44:37

He was very wrong about eels.

0:44:400:44:44

Whoa! It's a big one.

0:44:480:44:50

What a gorgeous fish.

0:44:540:44:57

Which kind is it? Is it leptocephalous?

0:45:020:45:04

-Leptocephalous.

-Leptocephalous.

0:45:040:45:06

Aristotle says that the eels grow from the mud

0:45:070:45:10

at the bottom of the rivers.

0:45:100:45:12

-Why would he say that?

-Because basically he sees eels,

0:45:120:45:18

even big ones, but especially small ones,

0:45:180:45:21

they hide in the mud, they can easily just

0:45:210:45:24

in the mud, just go... Go directly inside and disappear inside.

0:45:240:45:29

In the mud.

0:45:290:45:31

See, all this time, we never saw an eel with eggs.

0:45:310:45:35

So what do you think that tells us?

0:45:350:45:38

I don't know. This is a mystery.

0:45:400:45:43

This is a eel mystery. Nobody knows.

0:45:430:45:46

Well, marine biologists do know, but Aristotle certainly didn't.

0:45:460:45:52

-See, he turns?

-Yes.

0:45:540:45:57

So when they bite they turn like that...

0:45:570:46:00

I think we've got enough, don't you?

0:46:030:46:05

Yeah.

0:46:050:46:07

Aristotle noticed that eels are very unusual creatures.

0:46:130:46:19

If you do a ventral incision,

0:46:210:46:25

if you make a ventral incision of this sort,

0:46:250:46:28

in order to look at its internal organs...

0:46:280:46:31

..through to the rectum,

0:46:330:46:38

down beyond,

0:46:380:46:41

what you see are all the regular organs

0:46:430:46:46

that you would find in any fish.

0:46:460:46:49

But, in a regular fish,

0:46:510:46:56

the reproductive organs would be somewhere right around here,

0:46:560:47:01

the gonads, the sperm and the eggs.

0:47:010:47:03

However, in eels, you simply never find them. Aristotle noticed this,

0:47:030:47:07

and for him, it raised the obvious question,

0:47:070:47:10

how, if an eel doesn't have eggs or sperm, does it reproduce?

0:47:100:47:16

It's a reasonable question.

0:47:180:47:22

He could, of course, not know that the European eel develops its gonads

0:47:220:47:27

in the course of a 9,000 km swim

0:47:270:47:30

to its spawning grounds in the Sargasso Sea.

0:47:300:47:34

He seems to think that some kinds of creatures don't reproduce.

0:47:390:47:44

They just appear from nowhere.

0:47:440:47:48

-They "spontaneously generate", to use his term.

-That's right.

0:47:480:47:53

-What's all that about?

-He noticed that some animals

0:47:530:47:58

don't come about from animals of the same kind.

0:47:580:48:03

So humans can produce tapeworms or fleas

0:48:030:48:06

and he extends this to other animals, in other parts of nature,

0:48:060:48:12

in the sea above all, but also with almost all insects.

0:48:120:48:16

Quite why he does that is a very peculiar question.

0:48:190:48:22

For nearly 2,000 years after Aristotle,

0:48:230:48:27

as a consequence of Aristotle,

0:48:270:48:29

people believed that lots of different creatures,

0:48:290:48:33

insects, snails, clams, spontaneously generated,

0:48:330:48:36

that they didn't actually ever reproduce.

0:48:360:48:38

It had immense influence on biology.

0:48:380:48:40

A disaster.

0:48:400:48:43

One of Aristotle's less happy theories.

0:48:430:48:46

Less happy theories?

0:48:460:48:47

One of his catastrophic mistakes, I would say.

0:48:470:48:50

Aristotle observed that putrefying flesh

0:48:540:48:57

often seems to breed other creatures.

0:48:570:49:01

Take this European glass lizard, which we have conveniently

0:49:030:49:07

found dead at the side of a road.

0:49:070:49:12

I'm cutting it up in order to see what's inside.

0:49:140:49:18

The lizard has become rather mummified in the intense heat.

0:49:240:49:29

We see, perhaps unsurprisingly,

0:49:320:49:37

that it's crawling with maggots.

0:49:370:49:42

Now, Aristotle knows that

0:49:450:49:49

flies come from maggots

0:49:490:49:52

and he knows that maggots come from

0:49:520:49:56

putrefying flesh.

0:49:560:49:59

And so he concludes,

0:49:590:50:01

not unreasonably,

0:50:010:50:04

that flies are, in his words, "spontaneously generated"

0:50:040:50:09

from dead things.

0:50:090:50:13

-You find these just here in Kalloni?

-Just here in port.

0:50:160:50:20

The fish from Kalloni, are they nice?

0:50:200:50:22

-They are the very best.

-The best. And I'll take one of these guys.

0:50:220:50:26

Aristotle's belief in spontaneous generation wasn't, however,

0:50:260:50:31

the real reason he became discredited.

0:50:310:50:33

Rather, it was the failings in his method that this belief exposed.

0:50:330:50:38

When I read Aristotle, it's like reading the work

0:50:380:50:40

of a brilliant, albeit eccentric, colleague.

0:50:400:50:44

There are the same detailed observations,

0:50:440:50:47

the closely argued theory,

0:50:470:50:50

the same invidious references to predecessors.

0:50:500:50:54

But there's one thing that's missing,

0:50:540:50:58

the thing that defines modern science...

0:50:580:51:04

..experiment.

0:51:070:51:09

I place two fresh fish in two jars,

0:51:130:51:15

cover one with gauze and leave the other exposed.

0:51:150:51:20

It's the kind of experiment that Aristotle might have done,

0:51:200:51:23

but didn't.

0:51:240:51:25

A week later, I look at the results.

0:51:250:51:29

This fish has been left open

0:51:300:51:33

and exposed to the elements.

0:51:330:51:36

And it is

0:51:400:51:43

crawling with maggots.

0:51:430:51:47

Such as this one here.

0:51:510:51:54

And the fish that has been covered in gauze, by contrast,

0:52:040:52:07

there's plenty of rotting meat,

0:52:070:52:10

but there aren't any maggots.

0:52:100:52:13

And that proves that in order to get maggots in rotting meat

0:52:150:52:19

you first have to get flies that lay eggs in them.

0:52:190:52:23

And that, in all its simplicity,

0:52:230:52:25

was the experiment that Francesco Redi did in 1668.

0:52:250:52:30

It demolished Aristotle's theory of spontaneous generation.

0:52:300:52:33

And his reputation never recovered.

0:52:330:52:37

At the heart of this story lies a tragic paradox.

0:52:580:53:01

For nearly 2,000 years, when men inquired about the natural world,

0:53:010:53:06

they first asked, "What did Aristotle think?"

0:53:060:53:10

And such was the force of his mind and the scope of his investigations

0:53:100:53:14

that invariably he had an answer.

0:53:140:53:16

And that was the problem.

0:53:230:53:25

Aristotle, or rather his epigones, became an impediment to progress.

0:53:250:53:30

The battle cry of modern science was sounded,

0:53:300:53:33

"Study nature, not books" and by that, they meant Aristotle's books.

0:53:330:53:39

He was turned into a symbol of the muddleheaded past

0:53:420:53:47

and with some reason.

0:53:470:53:49

He was the giant who had to be slain

0:53:490:53:52

so that we could pass through the gates of philosophy

0:53:520:53:56

and reach the green fields of scientific truths that lay beyond.

0:53:560:54:01

Aristotle stayed in Lesvos for just two years.

0:54:060:54:11

He was offered a job, tutor to a princeling called Alexander,

0:54:110:54:17

whom history would call the Great.

0:54:170:54:20

Later, he returned to Athens,

0:54:200:54:23

where he founded his own philosophical school.

0:54:230:54:28

He thought, wrote and, in 322 BC, died.

0:54:280:54:34

What, then, are we to make of Aristotle?

0:54:410:54:44

Should we praise him for his prescience,

0:54:440:54:47

or condemn him for his errors?

0:54:470:54:50

I think he gives us this. He tells us that creatures

0:54:520:54:56

are exquisitely fitted to their environments.

0:54:560:54:59

That they are adapted and that adaptation requires an explanation.

0:54:590:55:05

He also says that complex things such as creatures cannot simply

0:55:050:55:08

self assemble from their constituent parts,

0:55:080:55:11

but rather that they need something else.

0:55:110:55:14

They need information.

0:55:140:55:17

And he tells us that if we want to understand living things,

0:55:170:55:21

we have to take them apart, we have to reduce them down

0:55:210:55:25

to their individual bits and pieces. But that once we have done so,

0:55:250:55:29

we also have to put them back together again.

0:55:290:55:32

For only when we do so will we really understand how they work.

0:55:320:55:36

And it is this that, I think, makes Aristotle speak to us today.

0:55:360:55:40

For if taking things apart was the task of 20th Century biology,

0:55:400:55:45

putting them back together again is the task of the 21st.

0:55:450:55:50

He is important because he gives us the very structure of our thought,

0:55:530:55:58

even when we do not know it ourselves.

0:55:580:56:01

His thought flows like a subterranean river

0:56:010:56:05

through the history of our science, surfacing now and then as a spring,

0:56:050:56:09

with ideas that are apparently new but are, in fact, very old.

0:56:090:56:14

Is this view of Aristotle anachronistic?

0:56:220:56:27

I don't think so.

0:56:270:56:29

He is so vast, so protean, that each generation must read him anew.

0:56:290:56:35

For when they do,

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they always find things in him that their predecessors have missed.

0:56:360:56:42

Aristotle wrote thousands of sentences, but one,

0:56:480:56:53

the first in his Metaphysics, defines him.

0:56:530:56:57

"All men", he says, "desire to know.

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"But not all forms of knowledge are equal, the best is

0:57:010:57:07

"the pure and disinterested search for the causes of things".

0:57:070:57:11

And, he has no doubt,

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"Searching for them is the best way to spend a life".

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It's a claim for the beauty and worth of science.

0:57:170:57:24

Subtitles by Red Bee Media Ltd

0:57:440:57:48

E-mail subtitling@bbc.co.uk

0:57:480:57:51

In the 4th century BC the Greek philosopher Aristotle travelled to Lesvos, an island in the Aegean teeming, then as now, with wildlife. His fascination with what he found there, and his painstaking study of it, led to the birth of a new science - biology. Professor Armand Leroi follows in Aristotle's footsteps to discover the creatures, places and ideas that inspired the philosopher in his pioneering work.