foxes not only behaved like domestic dogs, they looked like them. They lost their foxy pelage and became piebald black and white, like Welsh collies. Their foxy prick ears were replaced by doggy floppy ears. Their tails turned up at the end like a dog’s, rather than down like a fox’s brush. The females came on heat every six months like a bitch, instead of every year like a vixen. According to Belyaev, they even sounded like dogs.
Belayev with his foxes, as they turn tame – and doglike
These dog-like features were side-effects. Belyaev and his team did not deliberately breed for them, only for tameness. Those other dog-like characteristics seemingly rode on the evolutionary coattails of the genes for tameness. To geneticists, this is not surprising. They recognize a widespread phenomenon called ‘pleiotropy’, whereby genes have more than one effect, seemingly unconnected. The stress is on the word ‘seemingly’. Embryonic development is a complicated business. As we learn more about the details, that ‘seemingly unconnected’ turns into ‘connected by a route that we now understand, but didn’t before’. Presumably genes for floppy ears and piebald coats are pleiotropically linked to genes for tameness, in foxes as well as in dogs. This illustrates a generally important point about evolution. When you notice a characteristic of an animal and ask what its Darwinian survival value is, you may be asking the wrong question. It could be that the characteristic you have picked out is not the one that matters. It may have ‘come along for the ride’, dragged along in evolution by some other characteristic to which it is pleiotropically linked.
The evolution of the dog, then, if Coppinger is right, was not just a matter of artificial selection, but a complicated mixture of natural selection (which predominated in the early stages of domestication) and artificial selection (which came to the fore more recently). The transition would have been seamless, which again goes to emphasize the similarity – as Darwin recognized – between artificial and natural selection.
FLOWERS AGAIN
Let’s now, in the third of our warm-up forays into natural selection, move on to flowers and pollinators and see something of the power of natural selection to drive evolution. Pollination biology furnishes us with some pretty amazing facts, and the high point of wondrousness is reached in the orchids. No wonder Darwin was so keen on them; no wonder he wrote the book I have already mentioned, The Various Contrivances by which Orchids are Fertilised by Insects. Some orchids, such as the ‘magic bullet’ Madagascar ones we met earlier, give nectar, but others have found a way to bypass the costs of feeding pollinators, by tricking them instead. There are orchids that resemble female bees (or wasps or flies) well enough to fool males into attempting to copulate with them. To the extent that such mimics resemble females of one particular insect species, to that extent will males of those species serve as magic bullets, going from flower to flower of just the one orchid species. Even if the orchid resembles ‘any old bee’ rather than one species of bee, the bees that it fools will still be ‘fairly magic’ bullets. If you or I were to look closely at a fly orchid or a bee orchid (see colour page 5), we would be able to tell that it was not a real insect; but we would be fooled at a casual glance out of the corner of our eye. And even looking at it head-on, I would say the bee orchid in the picture (h) is pretty clearly more of a bumble-bee orchid than a honey-bee orchid. Insects have compound eyes, which are not so acute as our camera eyes, and the shapes and colours of insect-mimicking orchids, reinforced by seductive scents that mimic those of female insects, are more than capable of tricking males. By the way, it is quite probable that the mimicry is enhanced when seen in the ultraviolet range, from which we are cut off.
The
Belayev with his foxes, as they turn tame – and doglike
These dog-like features were side-effects. Belyaev and his team did not deliberately breed for them, only for tameness. Those other dog-like characteristics seemingly rode on the evolutionary coattails of the genes for tameness. To geneticists, this is not surprising. They recognize a widespread phenomenon called ‘pleiotropy’, whereby genes have more than one effect, seemingly unconnected. The stress is on the word ‘seemingly’. Embryonic development is a complicated business. As we learn more about the details, that ‘seemingly unconnected’ turns into ‘connected by a route that we now understand, but didn’t before’. Presumably genes for floppy ears and piebald coats are pleiotropically linked to genes for tameness, in foxes as well as in dogs. This illustrates a generally important point about evolution. When you notice a characteristic of an animal and ask what its Darwinian survival value is, you may be asking the wrong question. It could be that the characteristic you have picked out is not the one that matters. It may have ‘come along for the ride’, dragged along in evolution by some other characteristic to which it is pleiotropically linked.
The evolution of the dog, then, if Coppinger is right, was not just a matter of artificial selection, but a complicated mixture of natural selection (which predominated in the early stages of domestication) and artificial selection (which came to the fore more recently). The transition would have been seamless, which again goes to emphasize the similarity – as Darwin recognized – between artificial and natural selection.
FLOWERS AGAIN
Let’s now, in the third of our warm-up forays into natural selection, move on to flowers and pollinators and see something of the power of natural selection to drive evolution. Pollination biology furnishes us with some pretty amazing facts, and the high point of wondrousness is reached in the orchids. No wonder Darwin was so keen on them; no wonder he wrote the book I have already mentioned, The Various Contrivances by which Orchids are Fertilised by Insects. Some orchids, such as the ‘magic bullet’ Madagascar ones we met earlier, give nectar, but others have found a way to bypass the costs of feeding pollinators, by tricking them instead. There are orchids that resemble female bees (or wasps or flies) well enough to fool males into attempting to copulate with them. To the extent that such mimics resemble females of one particular insect species, to that extent will males of those species serve as magic bullets, going from flower to flower of just the one orchid species. Even if the orchid resembles ‘any old bee’ rather than one species of bee, the bees that it fools will still be ‘fairly magic’ bullets. If you or I were to look closely at a fly orchid or a bee orchid (see colour page 5), we would be able to tell that it was not a real insect; but we would be fooled at a casual glance out of the corner of our eye. And even looking at it head-on, I would say the bee orchid in the picture (h) is pretty clearly more of a bumble-bee orchid than a honey-bee orchid. Insects have compound eyes, which are not so acute as our camera eyes, and the shapes and colours of insect-mimicking orchids, reinforced by seductive scents that mimic those of female insects, are more than capable of tricking males. By the way, it is quite probable that the mimicry is enhanced when seen in the ultraviolet range, from which we are cut off.
The
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