ABSTRACT
Our biological sex is determined at birth by factors beyond our control, yet being born male or female is probably the most important feature of our lives. The first question generally asked about a new born baby is whether it is a boy or girl, just as the first thing we notice when we see someone for the first time is whether the person is male or female. Almost every official form we fill out requires us to say whether we are male or female. Physical appearance, dress, behavior, and language provide some of the most important means of identifying ourselves daily to others as male or female. When we see a baby dressed in pink with a frilly bonnet, we conclude it must be a girl. Even though unisex fashions have made gender boundaries increasingly less rigid, gender is still one of the most visible human traits;
80% of U.S. 2-year-olds can readily distinguish males from females on the basis of purely cultural cues like hairstyle and clothing.
