THE CENTRAL FACTS FROM THE COURSES YOU ALWAYS MEANT TO TAKE, IN 25 LECTURES

Week 1 Day 3 Evolution

Charles Darwin's daughter Annie was a delightful nine-year-old; tall and long-haired; fond of clambering on her father's lap to comb his clothes and hair before he went out; teasingly insisting that this was the only way to make him look right. So when she died, horribly vomiting to death with fever, just turned 10, why should Charles bother to hold back his fury at the Creator that could do this?

His response was to perfect a theory of evolution, looking at a new way of explaining how changes between life forms take place. For respectable Victorian opinion it was clear that God had created all life. If you found a rock sitting in a field you might believe that just anyone had dropped it, or even that the inanimate earth itself had pushed it up. But if you found a wondrous watch, all ticking and geared, or even better, if you found a complete human being, then clearly mere chance couldn't have flung its parts together.

It's the old "Argument from Design", lifted from Aquinas and Maimonedes, which had always kept even the most faith-shaken individuals in check. To undermine the Creator, the Argument from Design would have to be destroyed.

Darwin did this simply by showing an alternate way in which complex bodies could form. Look at the simplest mollusc. It has a few pigmented cells in its front, which respond, ever so faintly, to changes in the amount of light around. But look at some of the molluscs which developed from it. These have light-sensitive cells too, but they are recessed into a little pit. In the carnivorous Nautilus mollusc that pit is widened out into a hollow sphere, with only a small opening to the outside world.

That's the shape of a pinhole camera, and suddenly those simple cells at the back get a focused image of the world outside. Let the hole get a thin covering, or widen in the middle, and the focusing gets even better, for you now have an eye with a lens - and ultimately the view of the squid or octopus, peering at their undersea world with excellent vision. The stages are so easy, so "natural" for unguided matter to slip into, that the human eye developed almost the same way, even from entirely different ancestors.

So long as the useful stages are accumulated, then over the achingly long stretches of geological time our entire planet could fill up. Our planet already features fish that can fly, apes that surf the Internet, birds that can swim, and snakes that carry boxes of warning rattles.

Darwin's vision was so powerful that it was immediately taken up by anyone who wanted its authority to back their own biases. Churchmen quickly tried to take it over, saying how noble it was that creatures were constantly ascending in complexity and dignity. But Darwin was ready for this: species develop towards simplicity as well as complexity, he said, pointedly giving the example of parasitic worms. These often had an ancestral form that was mobile and could hunt food, but then, following his principles of maximum fitness for the available environment, had lost all their legs and hunting capacity. Simply dangling in the human gut was more efficient.

Economists said that Darwin's theory justified struggle. But direct competition only rarely drives evolution. Species often steer clear of each other, or develop forms of co-operation. They can go to spectacular lengths, like the shapes of certain flowers and those flying penises we call hummingbirds.

Even when direct competition does occur, the result tends to be a long sequence of miserable struggle, with no net improvement in either side's capacity over vast stretches of time. Cheetahs and gazelles have been tormenting each other for immense periods, with the fossil record showing little improvement in their body types over that time. Darwin himself had as little to do with struggle as possible: at one point, when his inherited investments were threatened by a stock market crash, he was terrified that he might have to work for a living, knowing as he did that it would end his chance of creative work.

But perhaps the greatest misconception is to forget that evolution keeps on working, even in species we think we've superseded. By all objective accounts this is the Age of the Bacteria, as it has been for several billion years. They utterly dominate us, both in terms of numbers and of total bulk. They've also continued cross-mutating and evolving - snatching fragments of useful DNA as needed - in exact accord with Darwin's principles. As Third World forests are destroyed, bacteria are increasingly unleashed from the environments where they've been in equilibrium. How long will it take before an Ebola infection mutates enough to survive airborne in a sneeze? Charles Darwin, who never entirely recovered from his daughter's death, would recognise the possible consequences only too well.

Tomorrow, Freud

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