Gwen Dewar, biological anthropologist and founder of the Web site Parenting Science, responds:

The urge to nibble cute creatures might be a case of getting one's wires crossed. In a recent study, researchers performed functional magnetic resonance imaging scans on women who unwittingly sniffed newborn infants. The odors activated reward-related areas of the brain, the same regions that trigger a pleasurable rush of dopamine when we get our hands on a desirable bit of food. A similar neural effect was reported in an earlier study where women viewed images of babies.

This research suggests that, to some degree, our brains respond in a parallel way when perceiving cuteness and seeking food, and perhaps our psychological experience of wanting to bite arises from that physiological overlap. Yet we may have other reasons to associate babies and biting. A kind of friendly “social biting” may be part of our evolutionary heritage.

Creatures throughout the primate world are often drawn to their species' offspring. Some Old World monkeys, for instance, will line up for the chance to handle another monkey's new baby, and nuzzling—rubbing one's nose and mouth against the baby—is one of the most common forms of handling.

None of this is real biting. When biting occurs, animals get hurt. Yet pseudo-biting, if you will, is prevalent, especially in the form of the teasing nips that mammals give one another during rough-and-tumble play. The reasons for this behavior are not entirely clear. When a puppy gently bites your hand, is he honing his motor skills? Rehearsing for real-life combat? Engaging in a friendly game?

All those explanations are possibilities, but what is interesting here is that play-biting generally happens between trusted allies. Primatologist Susan Perry in the anthropology department at the University of California, Los Angeles, and her colleagues have seen capuchin monkeys bite one another in careful, seemingly ritualistic ways, clamping down on fingers hard enough to trap them but apparently causing no pain. The researchers think the monkeys may be testing their social bonds, sending the message, “I'm so trustworthy, you can stick your finger in my mouth.”

So biting is not only for feeding or aggression. Behaviors that resemble biting—mouthing, nuzzling and gentle nips—seem to be a normal part of the friendly social repertoires of many mammals. Also, of course all mammals begin life as enthusiastic social nibblers, extracting milk from their mother's mammary glands by chomping down with their toothless jaws. Against this background, the impulse to gobble up an adorable baby does not seem so bizarre. It may be one more example of friendly, pseudo-biting—and a sign of good intentions.