National Geographic : 2012 Feb
• it dating back, in some form, to ancient Egypt.) Pliable skin served as a defense mechanism, allowing the dog to endure sharp-toothed bites without signi cant damage. A long and sturdy tail helped hunters to retrieve it from an animal's lair, badger in its mouth. e breeders gave no thought, of course, to the fact that while coaxing such weird new dogs into existence, they were also tinkering with the genes that determine canine anatomy in the rst place. Scientists since have assumed that under- neath the morphological diversity of dogs lay an equivalent amount of genetic diversity. A recent explosion in canine genomic research, however, has led to a surprising, and opposite, conclusion: e vast mosaic of dog shapes, colors, and sizes is decided largely by changes in a mere handful of gene regions. e di erence between the dachs- hund's diminutive body and the Rottweiler's mas- sive one hangs on the sequence of a single gene. e disparity between the dachshund's stumpy legs---known o cially as disproportionate dwarf- ism, or chondrodysplasia---and a greyhound's sleek ones is determined by another one. e same holds true across every breed and almost every physical trait. In a project called CanMap, a collaboration among Cornell Uni- versity, UCLA, and the National Institutes of Health, researchers gathered DNA from more than 900 dogs representing 80 breeds, as well as from wild canids such as gray wolves and coyotes. ey found that body size, hair length, fur type, nose shape, ear positioning, coat col- or, and the other traits that together de ne a breed's appearance are controlled by somewhere in the neighborhood of 50 genetic switches. e di erence between oppy and erect ears is determined by a single gene region in canine chromosome 10, or CFA10. e wrinkled skin of a Chinese shar-pei traces to another region, called HAS2. e patch of ridged fur on Rhode- sian ridgebacks? at's from a change in CFA18. Flip a few switches, and your dachshund be- comes a Doberman, at least in appearance. Flip again, and your Doberman is a Dalmatian. "The story that is emerging," says Robert Wayne, a biologist at UCLA, "is that the diversity in domestic dogs derives from a small genetic tool kit." Media reports about the gene for red hair, alcoholism, or breast cancer give the false im- pression that most traits are governed by just one or a few genes. In fact, the Tinkertoy genetics of dog morphology is a complete aberration. In nature, a physical trait or disease state is usually the product of a complex interaction of many genes, each one making a fractional contribution. Height in humans, for instance, is determined by the interaction of some 200 gene regions. So why are dogs so di erent? e answer, the researchers say, lies in their unusual evolution- ary history. Canines were the earliest domesti- cated animal, a process that started somewhere between 20,000 and 15,000 years ago, most likely when gray wolves began scavenging around human settlements. Dog experts di er on how active a role humans played in the next step, but eventually the relationship became a mutual one, as we began employing dogs for hunting, guarding, and companionship. Sheltered from the survival-of-the-fittest wilderness, those LIKE ITS ANCESTOR THE GRAY WOLF, THE BASENJI, ONE OF THE MOST ANCIENT BREEDS, DOESN'T BARK.