To survive, those early homo erectus had to be very protective of their mates, children, food supplies, watering hole, and the security of the campgrounds. Strangers, on many occasions, wanted to take what they saw. Those who were strong won the confrontation. A million years later, with a thin layer of social veneer, we still have our doubts about those who are new and different. A child with so little as a missing thumb due to a birth defect can be put through intolerable harassment and humiliation in school.
Cheerleaders fantasize about quarterbacks and vice versa.
Good genes search out good genes. Meanwhile, peer pressure reigns. We have to work very hard to teach our children respect for diversity and differences in people. That's the litany of young people on the Internet. For them, its the natural reaction to something that's different and not well understood.