Q. Why does my dog howl and moan at the sound of a harmonica?

Walpole

A. Time to take those harmonica lessons you've been putting off, J.T.

Actually, it has nothing to do with how well or poorly the harmonica is being played. Dogs don't howl, as some think, because a sound is hurting their ears. Those howls are the ancient cry of the wolf still embedded in your dog's genes.

Dr. Nicholas Dodman, director of the Animal Behavior Clinic at the Tufts Veterinary School, explains that dogs howl in response to sounds that trigger vestigial biological responses that were part of their ancestors 10,000 to 12,000 years ago, when most scientists think our human ancestors tamed wild animals into the dogs we know today.

Back then, the wild canid predecessors of today's dogs probably used howling ``like smoke signals, a kind of long-distance relay to carry messages farther than just one voice could,'' Dodman says. ``The message probably wasn't very complicated. It was likely, `I'm here. Pass it along.' Or something simple like that.''

Then, our human ancestors bred our dogs' ancestors to do the things humans wanted them to do, like protect them and their livestock, and stop doing things they didn't want them to do, like eating humans. Barking around the campfire for protection at night when something stirred in the darkness was a good trait. Howling all night keeping the humans awake, and calling in their human-eating relatives, was not. So those traits were bred out as wolves were domesticated.

The breeds that still howl the most, like the Siberian husky and the American Eskimo, weren't bred as much to become docile, quiet domestic pets, but rather to keep some of their useful wild animal traits.

Domesticating dogs also bred a lot of the intelligence out of them. Juvenile wolves are playful and friendly but not nearly as smart as the adults. An adult wolf, on the other hand, is a veritable animal Ph.D. compared to most dogs. But we bred dogs to be like juvenile wolves: safer to be around but not as smart.

But though we bred most of the howling out of them, we didn't eliminate it entirely. So when dogs hear a sound that triggers that ages-old response, they howl back, ``I'm here.'' Lots of sounds set them off, including a harmonica, another dog's howl, or even a human howling at the dog.

Dodman says you can take a pretty accurate census of the dog population in his hometown when the fire department siren goes off.