impulsive dogs

Man's best friend — the dog — is a versatile creature. Dogs can work as herders, guards, guide dogs and even provide therapy for hospitalized patients. But which dogs are suited to which tasks (and here I mean individuals, not breeds) must be uniquely determined. There are behavioral tests, to be sure, and now there seems to be yet another way to tell whether a dog's personality can suit it to the job of ministering to the sick. And strange as it may seem, whether or not the dog becomes prematurely gray (i.e. before the age of 4 years) could provide the key.

In a...