That is, the left half of the body should be exactly the same as the right half, with well-proportioned limbs. Randy Thornhill, an evolutionary biologist at the University of New Mexico in the United States, has been studying symmetry for the past 15 years. He used a scanner to input the faces and bodies of different people into a computer to measure the symmetry ratio. The survey results show that both sexes find the opposite sex with good body symmetry more attractive. Thornhill explained that this is a genetic advantage, indicating that a person has good survival ability, and at the same time, it shows that he/she is in very good health. In comparison, men's way of observing women is slightly different. They value the symmetry of women's faces more than their bodies.