Read Inside of a Dog: What Dogs See, Smell, and Know for Free Online Page B

century was a small, wild animal that had become popular with the fur trade. Kept in pens, bred for their choice fur coats, particularly long and soft, the fox was not tamed but was captive. What Belyaev made of them, with a much reduced recipe, were not "dogs," but were surprisingly close to dogs.
    Though Vulpes vulpes, the silver fox, is distantly related to wolves and dogs, it had never before been domesticated. Despite their evolutionary relatedness, no canids are fully domesticated other than the dog: domestication doesn't happen spontaneously. What Belyaev showed was that it can happen quickly. Beginning with 130 foxes, he selectively chose and bred those that were the most "tame," as he described it. What he really chose were those foxes that were the least fearful of or aggressive toward people. The foxes were caged, so aggression was minimal. Belyaev approached each cage and invited the fox to eat some food out of his hand.
    Some bit at him; some hid. Some took the food, reluctantly. Others took the food and also let themselves be touched and patted without fleeing or snarling. Still others accepted the food and even wagged and whimpered at the experimenter, inviting rather than discouraging interaction. These were the foxes Belyaev selected. By some normal variation in their genetic code, these animals were naturally calmer around people, even interested in people. None of them had been trained; all had the same, minimal exposure to human caretakers, who fed them and cleaned their bedding for their short lives.
    These "tame" foxes were allowed to mate, and their young were tested the same way. The tamest of those were mated, when they were old enough; and their young; and their young. Belyaev continued the work until his death, and the program has continued since. After forty years, three-quarters of the population of foxes were of a class the researchers called "domesticated elite": not just accepting contact with people, but drawn to it, "whimpering to attract attention and sniffing and licking"… as dogs do. He had created a domesticated fox.
    Later genomic mapping has revealed that forty genes now differ between Belyaev's tame foxes and the wild silver fox. Incredibly, by selecting for one behavioral trait, the genome of the animal was changed in a half century. And with that genetic change came a number of surprisingly familiar physical changes: some of the later-generation foxes have multicolored, piebald coats, recognizable in dog mutts everywhere. They have floppy ears and tails that curl up and over their backs. Their heads are wider and their snouts are shorter. They are improbably cute.
    All these physical characteristics came along for the ride, once a particular behavior was chosen and picked out. The behavior is not what affects the body; instead, both are the common result of a gene or set of genes. Single behaviors aren't dictated by genes, but they are made more or less likely by them. If someone's genetic makeup leads to having very high levels of a stress hormone, for instance, it doesn't mean that they will be stressed all the time. But it may mean that they have a lowered threshold for having the classic stress response—a raised heart rate and breathing rate, increased sweating, and so on—in some contexts where someone else doesn't have a stress response. Let's say this low-threshold character screams at her dog for barreling into her at the dog park. Her screaming at the poor pup certainly is not genetically obliged—genes don't know from dog parks, or even pups—but her neurochemistry, created from her genes, facilitated it happening when a situation presented itself.
    So, too, with the doglike foxes. Given what genes do,* even a small change in a gene—turning on slightly later than it otherwise might, say—could change the likelihood of both certain behaviors and certain forms of physical appearance. Belyaev's foxes show that a few simple developmental differences can have a