An attentive mother dog grooms her litter of newborn pups. She licks them and, with her nose, nudges those that wander off back into the group. Few images connote the nurturing relationship of a mother with her infants better than this. For us humans, it's nearly impossible to view such a scene and not feel intuitively that the mother's treatment of the pups is good for them -- that this is the way things ought to be. The warmth, wetness, and pressure of the mother's tongue must make her babies feel safe and cared for.... But then we think, "That's ridiculous. They're just puppies. They probably wouldn't know if the mother was there or not, except that she supplies their food. Their eyes aren't even open."

So, which is it? Do newborn animals benefit from the caresses of their mother's tongue, or are we just anthropomorphizing -- ascribing human values and motivations to animal behavior? Studies conducted on several species of mammals (especially rats and monkeys) suggest that touch during early stages of development is critical to an animal's physical and psychological well-being.

Most touch research has compared the development of animals under normal conditions with the development of animals deprived of touch. These studies have revealed strong correlations between touch deprivation and a variety of physiological, behavioral, and social problems in young animals.

Researchers found that young rats and monkeys, for example, tended to grow more slowly and have weaker immune systems when deprived of touch. They were also much less likely to be inquisitive as they grew older, rarely venturing far from the nest to learn about the outside world. For monkeys it also seems that the importance of touch is absolutely essential when it comes to establishing social bonds. Touch-deprived rhesus monkeys tended to be extremely aggressive toward other monkeys and exhibited behaviors consistent with the human emotions of anger and depression. Furthermore, monkeys that were deprived of touch when young went on to raise their own offspring in a similarly distant manner.

It's not difficult to understand why being raised without touch would interfere with socialization. What's surprising is that the lack of touch can have such profound effects on so many aspects of a young animal's life, from its immunity to its adventurousness. And there's little doubt that the same is true for humans, too.

Test the skin's range of sensitivity in this NOVA classroom activity.