Pavel Novotny

In human anatomical terms, the leg is the part of the lower limb that lies between the knee and the ankle, the thigh is between the hip and knee and the term "lower limb" is used to describe the colloquial leg. This article generally follows the common usage.

The leg from the knee to the ankle is called the cnemis (nee'mis) or crus. The calf is the back portion and the shin is the front.

Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually-guided manipulation and the lower limb's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adoption to bipedalism is not limited to the leg, however, but has also affected the location of the body's center of gravity, the reorganisation of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization to support and locomotion — in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adopted to pipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.

The characterization of a person as “beautiful”, whether on an individual basis or by community consensus, is often based on some combination of inner beauty, which includes psychological factors such as personality, intelligence, grace, charm and elegance, and outer beauty, which includes physical factors, such as health, youthfulness, symmetry, averageness, and complexion.

A common way to measure outer beauty, as based on community consensus, or general opinion, is to stage a beauty pageant, such as Miss Universe. Inner beauty, however, is more difficult to quantify, though beauty pageants often claim to take this into consideration as well.

A strong indicator of physical beauty is "averageness", or "koinophilia". When images of human faces are averaged together to form a composite image, they become progressively closer to the "ideal" image and are perceived as more attractive. This was first noticed in 1883, when Francis Galton, cousin of Charles Darwin, overlaid photographic composite images of the faces of vegetarians and criminals to see if there was a typical facial appearance for each. When doing this, he noticed that the composite images were more attractive compared to any of the individual images. Researchers have replicated the result under more controlled conditions and found that the computer generated, mathematical average of a series of faces is rated more favorably than individual faces. Evolutionarily it makes logical sense that sexual creatures should be attracted to mates who possess predominantly common or average features.

Another feature of beautiful women that has been explored by researchers is a waist-to-hip ratio of approximately 0.70 for women. The concept of waist-to-hip ratio (WHR) was developed by psychologist Devendra Singh of the University of Texas at Austin. Physiologists have shown that this ratio accurately indicates most women's fertility. Traditionally, in premodern ages when food was more scarce, overweight people were judged more attractive than slender. Beauty is not solely limited to the female gender. More often defined as 'bishōnen,' the concept of beauty in men has been particularly established throughout history in East Asia, and most notably, in Japan. This is distinct from the idea of being metrosexual, which focuses mainly on the behavior of men in traditionally feminine ways. Bishōnen refers to males with distinctly feminine features, physical characteristics establishing the standard of beauty in Japan and typically exhibited in their pop culture idols. The origin of such a preference is uncertain but it clearly exists even today.