Fur is used in reference to the hair of animals, usually mammals, particularly those with extensive body hair coverage that is generally soft and thick, as opposed to the stiffer bristles on most pigs. The term pelage – first known use in English c. 1828 – (French, from Middle French, from poil hair, from Old French peilss, from Latin pilus,) is sometimes used to refer to the body hair of an animal as a complete coat. Fur is also used to refer to animal pelts which have been processed into leather with the hair still attached. The words fur or furry are also used, more casually, to refer to hair-like growths or formations, particularly when the subject being referred to exhibits a dense coat of fine, soft "hairs." If layered, rather than grown as a single coat, it may consist of short down hairs, long guard hairs, and, in some cases, medium awn hairs. Mammals with reduced amounts of fur are often called "naked", as with the naked mole-rat, or "hairless", as with hairless dogs.
An animal with commercially valuable fur is known within the fur industry as a furbearer. The use of fur as clothing and/or decoration is considered controversial by some people: most animal welfare advocates object to the trapping and killing of wildlife, and to the confinement and killing of animals on fur farms.
Fur has been a major challenge for 3D computer graphics artists due to its visual complexity and physical properties. The first movie which made extensive use of CGI fur was Pixar's 2001 film Monsters, Inc.
Fur usually consists of two main layers:
- Down hair (known also as undercoat or ground hair) — the bottom layer consisting of wool hairs, usually wavy or curly without straight portions or sharp points; down hairs tend to be shorter, flat, curly, and more numerous than the top layer. Its principal function is thermoregulation; it maintains a layer of dry air next to the skin and repels water, thus providing thermal insulation.
- Guard hair — the top layer consisting of longer, generally coarser, nearly straight shafts of hair that protrude through the down hair layer. The distal ends of the guard hairs provide the externally visible layer of the coat of most mammals with well-developed fur. This layer of the coat displays the most marked pigmentation and gloss, including coat patterns adapted to display or camouflage. It is also adapted to shedding water and blocking sunlight, protecting the undercoat and skin from external factors such as rain and ultraviolet radiation. Many animals, such as domestic cats, erect their guard hairs as part of their threat display when agitated.
Mammals with well-developed down and guard hairs also usually have large numbers of awn hairs. These begin their growth much as guard hairs do, but change their mode of growth, usually when less than half the length of the hair has emerged. This portion of the hair is called awn. The rest of the growth is thin and wavy, much like down hair. In many species of mammals, the awn hairs comprise the bulk of the visible coat. The proximal part of the awn hair shares the function of the down hairs, whereas the distal part aids the water-shedding function of the guard hairs, though their thin basal portion prevents their being erected like true guard hairs.
The modern fur arrangement is known to have occurred as far back as docodonts, haramiyidans and eutriconodonts, with Castorocauda, Megaconus and Spinolestes preserving compound follicles with guard hair and underfur.
Mammals without fur
Hair is one of the defining characteristics of mammals, however, several species or breeds have considerably reduced amounts of fur. These are often called "naked" or "hairless".
Some mammals naturally have reduced amounts of fur. Some semiaquatic or aquatic mammals such as cetaceans, pinnipeds and hippopotamuses have evolved hairlessness, presumably to reduce resistance through water. The naked mole-rat has evolved hairlessness, perhaps as an adaptation to their subterranean life-style. Two of the largest extant mammals, the elephant and the rhinoceros, are largely hairless. The hairless bat is mostly hairless but does have short bristly hairs around its neck, on its front toes, and around the throat sac, along with fine hairs on the head and tail membrane. Sphynx cats are another example of hairless mammals. Most hairless animals cannot go in the sun for long periods of time, or stay in the cold for too long. 
Humans are the only primate species that have undergone significant hair loss. The hairlessness of humans compared to related species may be due to loss of functionality in the pseudogene KRTHAP1 (which helps produce keratin) in the human lineage about 240,000 years ago. Mutations in the gene HR can lead to complete hair loss, though this is not typical in humans.
Sheep have not become hairless, however, their pelage is usually referred to as "wool" rather than fur.
Humans have artificially selected some domesticated mammalian species to have breeds that are hairless. There are several breeds of hairless cats, perhaps the most commonly known being the Sphynx cat. Similarly, there are several breeds of hairless dogs. Other examples of artificially selected hairless animals include the hairless guinea-pig, nude mouse, and the hairless rat.
Use in clothing
In clothing, fur is usually leather with the hair retained for its aesthetic and insulating properties. Fur has long served as a source of clothing for hominoids including the Neanderthal. Animal furs used in garments and trim may be dyed bright colors or to mimic exotic animal patterns, or shorn down to imitate the feel of a soft velvet fabric. The term "a fur" is often used to refer to a fur coat, wrap, or shawl.
Usual animal sources for fur clothing and fur trimmed accessories include fox, rabbit, mink, beavers, ermine, otters, sable, seals, coyotes, chinchilla, raccoon, and possum. The import and sale of seal products was banned in the U.S. in 1972 over conservation concerns about Canadian seals. The import and sale is still banned even though the Marine Animal Response Society estimates the harp seal population is thriving at approximately 8 million. The import, export and sales of domesticated cat and dog fur were also banned in the U.S. under the Dog and Cat Protection Act of 2000.
The manufacturing of fur clothing involves obtaining animal pelts where the hair is left on the animal's processed skin. In contrast, making leather involves removing the hair from the hide or pelt and using only the skin. The use of wool involves shearing the animal's fleece from the living animal, so that the wool can be regrown but sheepskin shearling is made by retaining the fleece to the leather and shearing it. Shearling is used for boots, jackets and coats and is probably the most common type of skin worn.
Most animal rights activists are opposed to the trapping and killing of wildlife, and the confinement and killing of animals on fur farms. According to Humane Society International, over 8 million animals are trapped yearly for fur, while more than 30 million were raised in fur farms.
- Human activities
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- Thomson, Paul (2002). "Cheiromeles torquatus". Animal Diversity Web. Retrieved 29 October 2013.
- Winter, H.; Langbein, L.; Krawczak, M.; Cooper, D. N.; Jave-Suarez, L. F.; Rogers, M. A.; Praetzel, S.; Heidt, P. J.; Schweizer, J. (2001). "Human type I hair keratin pseudogene phihHaA has functional orthologs in the chimpanzee and gorilla: Evidence for recent inactivation of the human gene after the Pan-Homo divergence". Human Genetics 108 (1): 37–42. doi:10.1007/s004390000439. PMID 11214905.
- "Molecular evolution of HR, a gene that regulates the postnatal cycle of the hair follicle". Retrieved 2012-03-13.
- "Harp Seal", Marine Animal Response Society.
- Rules and Regulations Under the Fur Products Labeling Act.
- Australian Wool Corporation, Australian Wool Classing, Raw Wool Services, 1990.
- Chamber's journal, Published by Orr and Smith, 1952, pg 200, Original from the University of Michigan.
- Humane Society International Fur Trade.
- "Fur production, by province and territory".
- The fur industry. Peta, n.d.
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