Hair is a filamentous outgrowth from the skin, found mainly in mammals.
In some species, it is absent at certain stages of life. It projects from the epidermis, though it grows from hair follicles deep in the dermis. So-called "hairs" (trichomes) are also found on plants.
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The projections on arthropods, such as insects and spiders are actually insect bristles. The hair of non-human species is commonly referred to as fur. There are varieties of cats, dogs, and mice bred to have little or no visible hair.
Not all mammals have thick fur. Many aquatic mammals, such as whales and dolphins, have little or no body hair (though life in the water does not necessarily lead to hair loss, as the pinnipeds and otters demonstrate). |
A general inverse trend exists between body size and the thickness of body hair (measured in hair follicles per square centimeter). Large animals such as elephants and rhinoceros that have a higher ratio of body mass to surface area (and that need to keep from overheating) also have little or no body hair.
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