英语时差：东方的狗

Have you ever taken a good look at your dog and wondered, where did this creature come from? Sure, you know your dog came from the local shelter or a pet store, but what about before that? If you were able to trace your dog's lineage back to its origins, what would you find? Until recently, scientists believed that domestic dogs originated in the Middle East. But reports suggest that almost all domestic dogs began in East Asia as the offspring of three lineages. Virtually all domesticated dogs in the United States descend from dogs brought over by ancient people that crossed the Bering land bridge from Asia to North America. Although the New World had a healthy wolf population that might have given rise to a New World strain of domesticated dogs, by and large these ancient immigrants stuck with the dogs of Asian origin.

How, you may wonder, have scientists come to these conclusions? The same way forensic specialists increasingly solve crimes--through DNA evidence. Since mitochondria are cellular elements passed from mother to pup, mitochondrial DNA readily reveal genetic footprints stretching back into prehistoric times. Scientists from the Smithsonian Institution in Washington, D.C. collected DNA samples from the remains of ancient Old World dogs, ancient New World dogs, and ancient New World wolves. Test showed decisively that the New World dogs were genetically more similar to Old World dogs than to New World wolves, effectively proving that the dogs we save from local shelters originally hail from the far East rather than the woods of North America.