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which must breed by mixing their genes. Why do human beings have two sexes? Because in mobile animals hermaphrodites are less good at doing two things at once than males and females are at each doing his or her own thing. Therefore ancestral hermaphroditic animals were outmanoeuvred by ancestral sexed animals. But why only two sexes? Because that was the only way to settle a long-running genetic dispute between sets of genes. What? I’ll explain later. But why does she need him? Why don’t her genes just go ahead and make babies without waiting for his input? That is the most fundamental why question of all, and the one with which the next chapter begins.

In physics, there is no great difference between a why question and a how question. How does the earth go round the sun? By gravitational attraction. Why does the earth go round the sun? Because of gravity. Evolution, however, causes biology to be a very different game, because it includes contingent history. As the anthropologist Lionel Tiger has put it, ‘We are perforce in some sense constrained, goaded, or at least affected by the accumulated impact of selective decisions made over thousands of generations.’12 Gravity is gravity however history deals its dice. A peacock is a showy peacock because at some point in history ancestral peahens stopped picking their mates according to mundane utilitarian criteria and instead began to follow a fashion for preferring elaborate display. Every living creature is a product of its past. When a neo-Darwinian asks ‘Why?’ he is really asking ‘How did this come about?’ He is a historian.

Of Conflict and Cooperation

One of the peculiar features of history is that time always erodes advantage. Every invention sooner or later leads to a counter-invention. Every success contains the seeds of its own overthrow. Every hegemony comes to an end. Evolutionary history is no different. Progress and success are always relative. When the land was unoccupied by animals, the first amphibian to emerge from the sea could get away with being slow, lumbering and fish-like, for it had no enemies and no competitors. But if a fish were to take to the land today it would be gobbled up by a passing fox as surely as a Mongol horde would be wiped out by machine guns. In history, and in evolution, progress is always a futile, Sisyphean struggle to stay in the same relative place by getting ever better at things. Cars move through the congested streets of London no faster than horse-drawn carriages did a century ago. Computers have no effect on productivity because people learn to complicate and repeat tasks that have been made easier.13

This concept, that all progress is relative, has come to be known in biology by the name of the Red Queen, after a chess piece that Alice meets in Through the Looking Glass, who perpetually runs without getting very far because the landscape moves with her. It is an increasingly influential idea in evolutionary theory, and one that will recur throughout the book. The faster you run, the more the world moves with you and the less you make progress. Life is a chess tournament in which if you win a game, you start the next game with the handicap of a missing pawn.

The Red Queen is not present at all evolutionary events. Take the example of a polar bear, which is equipped with a thick coat of white fur. The coat is thick because ancestral polar bears better survived to breed if they did not feel the cold. There was a relatively simple evolutionary progression: thicker and thicker fur, warmer and warmer bears. The cold did not get worse just because the bear’s insulation got thicker. But the polar bear’s fur is white for a different reason: camouflage. White bears can creep up on seals much more easily than brown bears can. Presumably, once upon a time, it was easy to creep up on Arctic seals because they feared no enemies on the ice, just as present-day Antarctic seals are entirely fearless on the ice. In those days, proto-polar-bears had an easy time catching seals. But soon nervous, timid seals tended to live longer than trusting