Full nudity refers to complete nudity, while partial nudity refers to less than full nudity, with parts of the body covered in some manner. The term "partial nudity" is sometimes used to refer to exposure of skin beyond what the person using the expression considers to be within the limits of modesty. If the exposure is within the standards of modesty of a given culture and setting (e.g. wearing a bikini at a non-nude beach), terms such as nudity, partial or otherwise, are not normally used. If however, the degree of exposure exceeds the cultural norms of the setting, or if the activity or setting includes nudity as an understood part of its function, such as a nude beach, terminology relating to nudity and degrees thereof are typically used. Toplessness is regarded by most people as partial nudity.
Full frontal nudity describes a state of full nudity with the subject facing towards the viewer, with the whole front of the body exposed, including intimate parts such as a man's penis or woman's vulva. Partial frontal nudity typically only refers to the exposure of the breasts. Non-frontal nudity describes nudity where the whole back side of the body, including the buttocks, is exposed, or a side-view from any other direction.
Hair probably evolved in mammals before about 220 million years ago. The closest genetic relatives of humans, apes and especially chimpanzees, possess an almost complete covering of fur.
Humans are today the only naked primate in nature, that is, most of the body is not naturally covered by fur. Reliable information on the development of nudity and the passage of time are not yet possible because hair does not fossilize.
Researchers at the University of Utah in 2004 found that human skin contains photoreceptors like those in the retina, allowing it to mount an immediate defence against damaging ultraviolet radiations. They suspect that the protein that protects the skin from sunlight evolved following the loss of protective hair, which happened about 1.2 million years ago.