Variations in the physical appearance of humans, known as human looks, are believe by anthropologists to be an important factor in the development of personality and social relations in particular physical attractiveness. There is a relatively low sexual dimorphism between human males and females in comparison with other mammals. However humans are acutely sensitive to variations in physical appearance, some theorize for reasons of evolution. Some differences in human appearance are genetic, others are the result of age or disease, and many are the result of personal adornment.