A、Because people differ in their behavioral and physical characteristics. B、Because human fingerprints provide unique informatio

Faces, like fingerprints, are unique. Even a writer probably could not describe all the features that make one face different from another. Yet a very young child—or even an animal, such as a pigeon—can learn to recognize faces. We all take this ability for granted.
    We also tell people apart by how they behave. When we talk about someone’s personality, we mean the ways in which he or she acts, speaks, thinks and feels that make that individual different from others.
    Like the human face, human personality is very complex. But describing someone’s personality in words is somewhat easier than describing that person’s face. If you were asked to describe what a nice face looked like, you probably would have a difficult time doing so. But if you were asked to describe a nice person, you might begin to think about someone who was kind, considerate, friendly, warm, and so forth.
    There are many words to describe how a person thinks, feels and acts. Gordon Allport, an American psychologist, found nearly 18,000 English words characterizing differences in people’s behavior. And many of us use this information as a basis for describing with such terms.
    People have always tried to type each other. Actors in early Greek dramas wore masks to show the audience whether they played the villain’s or the hero’s role. In fact, the words "person" and "personality" come from the Latin persona, meaning mask. Today, most television and movie actors do not wear masks. But we can easily tell the good guys from the bad guys because the two types differ in appearance as well as action.