Raymond Coppinger points out that when domestic animals break free and go feral for many generations, they usually revert to something close to their wild ancestor. We might expect feral dogs, therefore to become rather wolf-like. But this doesn't happen. Instead, dogs left to go feral (wild) seem to become the ubiquitous 'village dogs' - 'pyre dogs' - that hang around human settlements all over the third world. Coppinger believes that the dogs on which which human breeders finally went to work were wolves no longer. They had already changed themselves into dogs: village dogs, pye-dogs, perhaps dingos.
The current consensus among biologists and archaeologists is that the dating of first domestication is indeterminate. There is conclusive evidence that dogs genetically diverged from their wolf ancestors at least 15,000 years ago, but some believe domestication to have occurred earlier. It is not known whether humans domesticated the wolf as such to initiate dog's divergence from its ancestors, or whether dog's evolutionary path had already taken a different course prior to domestication. Here is the story of an experiment that happened in Novosibirsk, Siberia that tries to prove the latter.
THE SILVER FOX EXPERIMENT
- a real life study in domestication
The silver fox is a melanistic colour variant of the familiar red fox, Vulpes vulpes. The Russian geneticist Dimitri Belyaev was employed to run a fox fur farm in the 1950s.
Domesticated Silver Fox
Wild foxes are tricky to handle, and Belyaev set out deliberately to breed for tameness. Like any other animal or plant breeder of his time, his method was to exploit natural variation (no genetic engineering in those days) and choose, for breeding, those males and females that came closest to the ideal he was seeking. In selecting for tameness, Belyaev could have chosen, for breeding, those dogs and bitches that most appealed to him, or looked at him with the cutest facial expressions. That might well have had the desired effect on the tameness of future generations. More systematically than that, however, he used a measure that was pretty close to the flight distance.
One of the main difference between wolf and dog behaviour is the flight distance. Real wolves are pack hunters. Village dogs are scavengers that frequent middens and rubbish dumps. Wolves scavenge too, but they are not temeperamentally suited to scavenging human rubbish because of their long flight distance. If you see an animal feeding, you can measure its flight distance by seeing how close it will let you approach before fleeing. For any given species in any given situation, there will be an optimal flight distance, somewhere between too risky or foolhardy and too flighty or risk averse. Individuals that take off too late when danger threatens are more likely to be killed by that danger. Individuals that are too flighty never get a square meal, because they run away at the first hint of danger on the horizon.
Belyaev and his colleagues (and successors, for the experimental program continued after his death) subjected fox cubs to standardized tests in which an experimenter would offer a cub food by hand, while trying to stroke or fondle it. The cubs were classified into three classes. Class III cubs were those that fled from or bit the person. Class II cubs would allow themselves to be handled, but showed no positive responsiveness to the experimenters. Class I cubs, the tamest of all, positively approached the handlers, wagging their tails and whining. When the cubs grew up, the experimenters systematically bred only from this tamest class.
After a mere six generations of this selective breeding for tameness, the foxes had changed so much that the experimenters felt obliged to name a new category, the domesticated elite class, which were eager to establish human contact, whimpering to attract attention and sniffing and licking experimenters like dogs. At the beginning of the experiment, none of the foxes were in the elite class. After 10 generations of breeding for tameness, 18 percent were elite. After 20 generations, 35 percent and after 30-35 generations, domesticated elite individuals constituted between 70 - 80 percent of the experimental population.
Such results are perhaps not too surprising, except for the astonishing magnitude and speed of the effect. 35 generations would pass unnoticed on the geological timescale. Even more interesting, however, were the unexpected side-effects of the selective breeding for tameness. The tame 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 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.
In fact, when USSR collapsed the fur farm was forced to find funds by selling 600 of their 700 silver foxes as pets. At last report, "Most of the project expenses are covered by selling the foxes as pets, but the project remains in a difficult situation, looking for new sources of revenue from outside funding."
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 coat-tails of the genes for tameness. To geneticists, this is not surprising. They recognize a widespread phenomenon called pleiotropy. 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 of evolution. When you notice a characterstic of an animal and ask what its Darwinian survival value is, you maybe 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).
In answer to the more controversial question, when did wolves suddenly evolve to dogs, this laboratory experiment gives a lower bound on how long it took. The true answer is somewhat still argued upon.
A couple of other findings with the Silver Fox experiments: The experimenters also breeded the most aggressive of silver foxes for comparison with domestic ones trying to find which genes controlled the aggressive behavior. The answer is not one particular set of genes but a lot of changes that controls the behavior. To the nurture v/s nature argument, they tried interchanging cubs of the tamer species with the aggressive ones and vice versa. But it doesnt matter what genes your surrogate mother has. The essential gene that controlled the aggressiveness and tameness still controlled the nature of the cub.
The silver fox is a melanistic colour variant of the familiar red fox, Vulpes vulpes. The Russian geneticist Dimitri Belyaev was employed to run a fox fur farm in the 1950s.
Domesticated Silver FoxWild foxes are tricky to handle, and Belyaev set out deliberately to breed for tameness. Like any other animal or plant breeder of his time, his method was to exploit natural variation (no genetic engineering in those days) and choose, for breeding, those males and females that came closest to the ideal he was seeking. In selecting for tameness, Belyaev could have chosen, for breeding, those dogs and bitches that most appealed to him, or looked at him with the cutest facial expressions. That might well have had the desired effect on the tameness of future generations. More systematically than that, however, he used a measure that was pretty close to the flight distance.
One of the main difference between wolf and dog behaviour is the flight distance. Real wolves are pack hunters. Village dogs are scavengers that frequent middens and rubbish dumps. Wolves scavenge too, but they are not temeperamentally suited to scavenging human rubbish because of their long flight distance. If you see an animal feeding, you can measure its flight distance by seeing how close it will let you approach before fleeing. For any given species in any given situation, there will be an optimal flight distance, somewhere between too risky or foolhardy and too flighty or risk averse. Individuals that take off too late when danger threatens are more likely to be killed by that danger. Individuals that are too flighty never get a square meal, because they run away at the first hint of danger on the horizon.
Belyaev and his colleagues (and successors, for the experimental program continued after his death) subjected fox cubs to standardized tests in which an experimenter would offer a cub food by hand, while trying to stroke or fondle it. The cubs were classified into three classes. Class III cubs were those that fled from or bit the person. Class II cubs would allow themselves to be handled, but showed no positive responsiveness to the experimenters. Class I cubs, the tamest of all, positively approached the handlers, wagging their tails and whining. When the cubs grew up, the experimenters systematically bred only from this tamest class.
After a mere six generations of this selective breeding for tameness, the foxes had changed so much that the experimenters felt obliged to name a new category, the domesticated elite class, which were eager to establish human contact, whimpering to attract attention and sniffing and licking experimenters like dogs. At the beginning of the experiment, none of the foxes were in the elite class. After 10 generations of breeding for tameness, 18 percent were elite. After 20 generations, 35 percent and after 30-35 generations, domesticated elite individuals constituted between 70 - 80 percent of the experimental population.
Such results are perhaps not too surprising, except for the astonishing magnitude and speed of the effect. 35 generations would pass unnoticed on the geological timescale. Even more interesting, however, were the unexpected side-effects of the selective breeding for tameness. The tame 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 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.
In fact, when USSR collapsed the fur farm was forced to find funds by selling 600 of their 700 silver foxes as pets. At last report, "Most of the project expenses are covered by selling the foxes as pets, but the project remains in a difficult situation, looking for new sources of revenue from outside funding."
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 coat-tails of the genes for tameness. To geneticists, this is not surprising. They recognize a widespread phenomenon called pleiotropy. 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 of evolution. When you notice a characterstic of an animal and ask what its Darwinian survival value is, you maybe 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).
In answer to the more controversial question, when did wolves suddenly evolve to dogs, this laboratory experiment gives a lower bound on how long it took. The true answer is somewhat still argued upon.
A couple of other findings with the Silver Fox experiments: The experimenters also breeded the most aggressive of silver foxes for comparison with domestic ones trying to find which genes controlled the aggressive behavior. The answer is not one particular set of genes but a lot of changes that controls the behavior. To the nurture v/s nature argument, they tried interchanging cubs of the tamer species with the aggressive ones and vice versa. But it doesnt matter what genes your surrogate mother has. The essential gene that controlled the aggressiveness and tameness still controlled the nature of the cub.
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