In human beings, some Characteristics can be easily explained but with some human traits, we really have no Idea why they occur. Each of these traits has a "clinical profile," the sum total of clues we have from looking at the outside, clinical level. They are mysteries waiting to be biologically solved on the inside, the mystery of what creates them: eye color, height, cystic fibrosis, cancer, intelligence, Tay Sachs, baldness, athletic ability, resistance to some viruses and susceptibility to others, skin tone, muscle mass, allergies and sex ....