" Our ancestors had access to two types of observable evidence of a woman’s health and youth: features of physical appearance, such as full lips, clear skin, smooth skin, clear eyes, lustrous hair, and good muscle tone, and features of behavior, such as a bouncy, youthful gait, an animated facial expression, and a high energy level. These physical cues to youth and health, and hence to reproductive capacity, constitute key elements of male standards of female beauty. "

― David M. Buss , The Evolution Of Desire: Strategies of Human Mating