Everyone knows that Aristotle was a great thinker. He invented logic, he wrote the Politics, Poetics and Metaphysics -- philosophers read them still. But fewer people know that he was also a great scientist -- and the first one. He was the first person to understand that theories about how the natural world works have to be tested by the evidence of our senses: by empirical reality. He wrote about physics, cosmology and chemistry but, above all, he loved biology. He collected thousands of facts about animals and plants and then, in a dozen books, explained them. It's the greatest scientific system ever erected by one man. But even Aristotle's greatest fans -- and I count myself among them -- have to concede that he got some things wrong.
1. Women are monstrous.
Aristotle says that women have fewer teeth than men. It's unclear why he thinks this. Maybe he counted his young wife's teeth and found she didn't have her wisdoms. But teeth are the least of Aristotle's problems with women. Compared to men, he says, they are "immature," "deficient," "deformed"; they are even a bit "monstrous."
Feminist scholars have made much of this. As well they might. But it's all of a piece with Aristotle's biology. He thinks that men have hotter blood than women, have a more important role in reproduction, and are generally more perfect. He does give some evidence for his remarks. He notes that if you "mutilate" a boy -- lop off his testicles -- his voice never breaks and he never grows bald: he becomes feminized. The inference that women are naturally mutilated men is reasonable, even if it doesn't exactly follow.
It's hard to resist the conclusion that Aristotle's views on female biology are at least partly conditioned by the patriarchal mores of his day. In his Politics he doesn't even consider the possibility that women could be citizens. To his credit, he objects to Plato's suggestion in The Republic that women should be communally shared. That, however, isn't a claim for women's rights: he just thinks that state-enforced sharing of women will lead to trouble. He was probably right.
2. Some people deserve to be slaves.
Fourth-century Athens ran on slaves. In his Politics Aristotle considers the justice of this. He concedes that prisoners of war don't deserve to be enslaved: they're free men who just got unlucky. But he also argues that some people do deserve to be enslaved. "Natural" slaves are the sort of people who have the ability to take orders, but aren't smart enough to think for themselves. They're machine people. They're not much better than animals.
It's a pretty harsh assessment. Set the question of ownership aside, however, and you can see what Aristotle is getting at. He'd understand modern industrial capitalism. He'd point out that the workers at a "fulfillment centre" of the sort that mail order firms run, who robotically obey the orders of roving "controllers," are slaves in the sense that that they can't exercise their reason. Are they "natural" slaves? Are they are incapable of exercising reason? No. But that is how they're treated.
3. Eels don't reproduce.
Eels are problem for Aristotle. His problem is that they don't have gonads. Cut one open, and you don't find the sperm and eggs that you find inside other fish. How, then, do they reproduce? Aristotle's solution is that they don't: they just spontaneously generate from mud. Of course, Aristotle couldn't have known about the European eel's bizarre life history: how it only develops its gonads as it makes a 6000 mile journey from Greek rivers to the Sargasso Sea off Bermuda; how it spawns at depth, dies, and how the tiny elvers make the long journey back. Still, his solution to the eel problem was excessively radical. In fact, he thinks quite a lot of animals -- flies, lice, midges, oysters, clams -- also spontaneously generate out of inanimate stuff. The theory of spontaneous generation was enormously influential. It was only in 1668 that Francesco Redi, an Italian scientist, showed that to get flies from rotten meat, other flies first have to lay eggs in it. Redi's experiment was simple. Aristotle could have done it. He didn't.
4. The eternity of the world.
Aristotle, a superb naturalist, has much of the evidence for evolution in front of him. He sees how species can be grouped into families; he sees how they are adapted to their environments, and he's got a theory of inheritance -- the most sophisticated one around until Mendel published in 1866. Some of his predecessors, the Pre Socratic philosophers, had quasi-evolutionary theories to account for the origin of life. Aristotle considers, and rejects, them all.
You might imagine that he thinks that some divine intelligence made the world; that he's a creationist. Plato, his teacher, was. But not Aristotle. He's something much stranger: he's an eternalist. He thinks that the cosmos, the earth, and all the species of animals and plants it contains have been there for ever. From his point of view, creationists and evolutionists aren't very different; they've both made the same mistake: they both think that the world began.
Why does Aristotle not get evolution? There's one kind of evidence he never mentions: fossils. Ancient travelers had talked about "stone fishes" on the top of mountains or clams in the middle of deserts, and wondered how they got there. Aristotle knew their books, but ignores such talk. Perhaps if you're committed to the eternity of species, a fossil bed just seems like a field of stones.
5. There's life out there.
Aristotle was a geocentrist. He thought that the earth sits at the centre of the cosmos: the sun, moon, planets and stars, embedded in crystalline spheres, revolve around it. Copernicus, Galileo and Kepler showed that he was wrong. The strangest aspect of Aristotle's cosmology, however, is not its geocentrism, but his conviction that the celestial objects are alive. They are, in fact, the most perfect living things; they're almost gods. He wonders why the moon doesn't have wings, and concludes that it doesn't need them; it's got a better way of motoring along. It's all part of his conviction that the cosmos, in all its glittering perfection, has a purpose. We don't; we just think that it just is.
This is Aristotle's astrotheology. His ultimate God is the Prime Mover; an immaterial entity who lives beyond the stars, and indifferent to life on earth, just spends his time thinking about thinking. The stars and the plants desire to be like Him and so rotate eternally. That's why living things reproduce: they want to be like God, eternal. For Aristotle, love literally makes the world go round.
6. How bees reproduce.
Aristotle tries to work out how bees reproduce. Most animals (spontaneous generators aside) have males and females, and it's easy to tell which is which. But bees come in three types: workers, drones and "leader" bees, our queens. He gathers all the data that he can, analyses it, and gives a life cycle for bees that, although ingenious, is wrong. But it's what he says at the end of his bee chapter that matters:
So this, at least as far as theory goes, seems to be the situation on the generation of bees -- in conjunction, that is, with what people believe to be the facts about their behavior. Not that there is, currently, any proper understanding of what those facts are. If in the future they are understood, it will be when the evidence of the senses is relied on more than theories, though theories have a part to play so long as what they indicate agrees with the facts.
This is what I think is going on, but I don't really know. When trying to understand the world, we should consider theories. But, really, it's the facts that matter; and if the facts change, our theories should too. It's a statement about how to do science, one made 23 centuries ago, the first. It's why, as a scientist, I can understand what Aristotle is saying. It's why I love him so.
Armand Marie Leroi's book, The Lagoon: How Aristotle Invented Science (Viking, $29.95) is published by Viking.