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stoat-like intermediates, until eventually, without ever noticing an abrupt change of any kind, we arrive at a leopard.
    Various things must be said about this thought experiment. First, we happen to have chosen to walk from rabbit to leopard, but I repeat that we could have chosen porcupine to dolphin, wallaby to giraffe or human to haddock. The point is that for any two animals there has to be a hairpin path linking them, for the simple reason that every species shares an ancestor with every other species: all we have to do is walk backwards from one species to the shared ancestor, then turn through a hairpin bend and walk forwards to the other species.
    
    
    Second, notice that we are talking only about locating a chain of animals that links a modern animal to another modern animal. We are most emphatically not evolving a rabbit into a leopard. I suppose you could say we are de- evolving back to the hairpin, then evolving forwards to the leopard from there. As we’ll see in a later chapter, it is unfortunately necessary to explain, again and again, that modern species don’t evolve into other modern species, they just share ancestors: they are cousins. This, as we shall see, is also the answer to that disquietingly common plaint: ‘If humans have evolved from chimpanzees, how come there are still chimpanzees around?’
    Third, on our forward march from the hairpin animal, we arbitrarily choose the path leading to the leopard. This is a real path of evolutionary history, but, to repeat this important point, we choose to ignore numerous branch points where we could have followed evolution to countless other end points – for the hairpin animal is the grand ancestor not only of rabbits and leopards but of a large fraction of modern mammals.
    The fourth point, which I have already emphasized, is that, however radical and extensive the differences between the ends of the hairpin – rabbit and leopard, say – each step along the chain that links them is very, very small. Every individual along the chain is as similar to its neighbours in the chain as mothers and daughters are expected to be. And more similar to its neighbours in the chain, as I have also mentioned, than to typical members of the surrounding population.
    You can see how this thought experiment drives a coach and horses through the elegant Greek temple of Platonic ideal forms. And you can see how, if Mayr is right that humans are deeply imbued with essentialist preconceptions, he might well also be right about why we historically found evolution so hard to stomach.
    
    
    The word ‘essentialism’ itself wasn’t invented till 1945 and so was not available to Darwin. But he was only too familiar with the biological version of it in the form of the ‘immutability of species’, and much of his effort was directed towards combating it under that name. Indeed, in several of Darwin’s books – more so in others than On the Origin of Species itself – you’ll understand fully what he’s on about only if you shed modern presuppositions about evolution, and remember that a large part of his audience would have been essentialists who never doubted the immutability of species. One of Darwin’s most telling weapons in arguing against this supposed immutability was the evidence from domestication, and it is domestication that will occupy the rest of this chapter.
    Sculpting the gene pool
    Darwin knew plenty about animal and plant breeding. He communed with pigeon fanciers and horticulturalists, and he loved dogs.* Not only is the first chapter of On the
Origin of Species all about domestic varieties of animals and plants; Darwin also wrote a whole book on the subject. The Variation of Animals and Plants under Domestication has chapters on dogs and cats, horses and asses, pigs, cattle, sheep and goats, rabbits, pigeons (two chapters; pigeons were a particular love of Darwin), chickens and various other birds, and plants, including the amazing cabbages. Cabbages are