“Find out where all the short-legged dogs come from,” an acquaintance told me, just before I left for Rarotonga, the capital island of the Cook Islands. Given that I was going to work as a veterinarian and that I had volunteered to collect DNA samples for the canine genome project, the request didn’t come entirely out of left field. Still, it seemed like some sort of inside joke.
Once I arrived, everything began to make sense. There are a lot of dogs on the island, most of them reminiscent of dingoes, like feral dogs the world over. But a good third of them have legs almost as short as a dachshund’s—though straight and lovely rather than crooked like those of most dwarf breeds. I guessed that these short-legged dogs descended from some distant European ancestor, some basset hound on holiday. But that thought only proved how little I knew about the origins of dogs and other domesticated animals.
Short legs, it turns out, aren’t that rare. The characteristic may even be a function of domestication. Animals don’t just become tame when they adapt to human society. They often become smaller, spotted, pug-nosed, floppy eared, oversexed, and small brained. They do this no matter what the species, genus, or taxon—dog, cat, cow, horse, sheep, pig. When natural selection narrows its focus on a single trait—docility—a suite of other traits tumble along behind. And those traits offer insight into biological development.
“Not one of our domestic animals can be named which has not in some country drooping ears,” Charles Darwin noted in The Origin of Species. His theory of natural selection was based in part on what he observed in domesticated species. Now genes dominate evolutionary theory, but some scientists argue that geneticists are missing something: DNA sequences alone can’t explain the many forms that species take. By looking closely at domesticated animals, they say, we may be able to unlock the mystery of how genotypes give rise to phenotypes—how nearly identical stretches of DNA can create radically different dogs.
