Few relationships are so laden with mutual benefit as that between man and dog. Much of the credit for this unusual state of affairs, it now turns out, may lie on the canine side of the equation.

Three studies in today's issue of Science shed light on the questions of when, where and how dogs were first domesticated from wolves. One suggests that a few wolves, perhaps from the same population somewhere in east Asia, are the mothers of almost all dogs alive today.

Despite some researchers' belief that dogs were domesticated independently in the Old World and in the New, domestication may have happened only once, probably around 15,000 years ago. Dogs seem quickly to have become highly prized and were brought along by the settlers who reached North America via the land bridge across the Bering Strait until the last ice age. This is the conclusion of a second study, based on DNA retrieved from ancient dog bones from Mexico, Bolivia and Peru, which found that all the pre-Columbian dogs belonged to Eurasian dog lineages.

A third study probes the psychology of dogs, showing that although chimpanzees may have brain power of far greater wattage, there is one task at which dogs excel, that of picking up cues from human behavior. This interpretive skill was perhaps the ability for which they were selected.