Last Sunday, the New York Times Magazine published a fascinating story on the burgeoning field of animal-personality research. The very idea that animals would have personalities challenges our traditional concepts of psychology and the difference between man and beast, of course. But as the writer Charles Siebert argues, studying animal behavior helps us figure out what precisely a personality is, and what it isn’t. What function does a personality serve, anyway? Why do we have one?

That latter point turns out to be the most interesting question in the whole story. Because when you think about it, a personality doesn’t always seem like a usefully adaptive behavior, in evolutionary terms. As Siebert writes:

“[Why] do we even have a personality?” he asked. “Why do we have a relatively narrow range of responses as opposed to a full range? Why can’t we all be bold when we need to be and cautious and shy when we need to be? Then we’d have no identifiable personality, and that would free us all to become optimal.”

For Sih, the answer seems to be that our personality is a manifestation of a complex interplay between genetic inheritance and environment and early-life experience. Bold people, for example, are both naturally disposed to boldness and, further, choose to be bold, becoming ever better at it, building from an early age a mountain of abilities and tendencies that become a personality. It might happen, as well, that an inherently shy person is induced by an early-life experience to venture away from his or her natural disposition and cultivate a bold personality. But whether a person ends up building and climbing a shy or a bold mountain, it may become increasingly difficult to come back down and build another one.

As one of the researchers in the article notes, a human that actually was able to morph his or her personality to adapt to an environment would be “scary to be around”.