This is an example of sexual dimorphisim. It is certainly not unique to humans. Females (in general) have a greater biological investment into reproduction, this makes them the chooser while the male will mate with just about anything. In species where the male has a greater investment in raising the offspring (some bird species as an example), the roles are reversed and the male is the chooser while the females will wantingly mate with multiple partners. Everyone doesn't need to want to have children, evolution only requires a sufficient number (or accidents) to continue the species.