Like many mammals,grizzly bears are covered in thick fur.
Afur is asoft, thick growth ofhair that covers theskin of almost allmammals. It consists of a combination of oilyguard hair on top and thickunderfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as aninsulating blanket that keeps the animal warm.[1]
The fur of mammals has many uses: protection, sensory purposes, waterproofing, and camouflaging, with the primary usage being thermoregulation.[2] The types of hair include[3]: 99
definitive, which may beshed after reaching a certain length;
vibrissae, which are sensory hairs and are most commonly whiskers;
pelage, which consists of guard hairs, under-fur, andawn hair;
spines, which are a type of stiff guard hair used for defense in, for example,porcupines;
bristles, which are long hairs usually used in visual signals, such as themane of a lion;
velli, often called "down fur", which insulates newborn mammals; and
Hair length is negligible in thermoregulation, as some tropical mammals, such as sloths, have the same fur length as some arctic mammals but with less insulation; and, conversely, other tropical mammals with short hair have the same insulating value as arctic mammals. The denseness of fur can increase an animal's insulation value, and arctic mammals especially have dense fur; for example, themuskox has guard hairs measuring 30 cm (12 in) as well as a dense underfur, which forms an airtight coat, allowing them to survive in temperatures of −40 °C (−40 °F).[3]: 162–163 Some desert mammals, such as camels, use dense fur to prevent solar heat from reaching their skin, allowing the animal to stay cool; a camel's fur may reach 70 °C (158 °F) in the summer, but the skin stays at 40 °C (104 °F).[3]: 188 Aquatic mammals, conversely, trap air in their fur to conserve heat by keeping the skin dry.[3]: 162–163
Mammalian coats are colored for a variety of reasons, the major selective pressures includingcamouflage,sexual selection, communication, and physiological processes such as temperature regulation. Camouflage is a powerful influence in many mammals, as it helps to conceal individuals from predators or prey.[4]Aposematism, warning off possible predators, is the most likely explanation of the black-and-white pelage of many mammals which are able to defend themselves, such as in the foul-smellingskunk and the powerful and aggressivehoney badger.[5] In arctic and subarctic mammals such as thearctic fox (Vulpes lagopus),collared lemming (Dicrostonyx groenlandicus),stoat (Mustela erminea), andsnowshoe hare (Lepus americanus),seasonal color change between brown in summer and white in winter is driven largely by camouflage.[6] Differences in female and male coat color may indicate nutrition and hormone levels, important in mate selection.[7] Some arboreal mammals, notably primates and marsupials, have shades of violet, green, or blue skin on parts of their bodies, indicating some distinct advantage in their largelyarboreal habitat due toconvergent evolution.[8] The green coloration of sloths, however, is the result of asymbiotic relationship with algae.[9] Coat color is sometimessexually dimorphic, as inmany primate species.[10] Coat color may influence the ability to retain heat, depending on how much light is reflected. Mammals with darker colored coats can absorb more heat from solar radiation and stay warmer; some smaller mammals, such asvoles, have darker fur in the winter. The white, pigmentless fur of arctic mammals, such as the polar bear, may reflect more solar radiation directly onto the skin.[3]: 166–167 [2]
The termpelage – first known use in Englishc. 1828 (French, from Middle French, frompoil for 'hair', fromOld Frenchpeilss, fromLatinpilus[11]) – is sometimes used to refer to an animal's completecoat. The term fur is also used to refer to animal pelts that have been processed into leather with their hair still attached. The wordsfur orfurry 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 singlecoat, it may consist of short down hairs, longguard hairs, and in some cases, mediumawn hairs. Mammals with reduced amounts of fur are often called "naked", as with thenaked mole-rat, or "hairless", as withhairless dogs.
An animal with commercially valuable fur is known within thefur industry as afurbearer.[12] The use offur as clothing or decoration is controversial;animal welfare advocates object to the trapping and killing of wildlife, and the confinement and killing of animals onfur farms.
Down hair (also known asunderfur,undercoat,underhair orground hair) is the bottom – or inner – layer, composed of wavy or curly hairs with no straight portions or sharp points. Down hairs, which are also flat, tend to be the shortest and most numerous in the coat.Thermoregulation is the principal function of the down hair, which insulates a layer of dry air next to the skin.
Theawn hair can be thought of as a hybrid, bridging the gap between the distinctly different characteristics of down and guard hairs. Awn hairs begin their growth much like guard hairs, but less than halfway to their full length, awn hairs start to grow thin and wavy like down hair. Theproximal part of the awn hair assists in thermoregulation (like the down hair), whereas thedistal part can shed water (like the guard hair). The awn hair's thin basal portion does not allow the amount ofpiloerection that the stiffer guard hairs are capable of. Mammals with well-developed down and guard hairs also usually have large numbers of awn hairs, which may even sometimes be the bulk of the visible coat.
Guard hair (overhair[13]) is the top—or outer—layer of the coat. Guard hairs are longer, generally coarser, and have nearly straight shafts that protrude through the layer of softer down hair. Thedistal end of the guard hair is the visible layer of most mammal coats. This layer has the most markedpigmentation andgloss, manifesting as coat markings that are adapted forcamouflage or display. Guard hair repels water and blocks sunlight, protecting the undercoat and skin in wet or aquatic habitats, and from the sun'sultraviolet radiation. Guard hairs can also reduce the severity ofcuts or scratches to the skin. Many mammals, such as the domestic dog and cat, have apilomotor reflex that raises their guard hairs as part of athreat display when agitated.
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"[citation needed] or "hairless".[14]
Some mammals naturally have reduced amounts of fur. Somesemiaquatic oraquatic mammals such ascetaceans,pinnipeds andhippopotamuses have evolved hairlessness, presumably to reduce resistance through water. Thenaked mole-rat has evolved hairlessness, perhaps as an adaptation to their subterranean lifestyle. Two of the largest extant terrestrial mammals, theelephant and therhinoceros, are largely hairless. Thehairless 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. Most hairless animals cannot go in the sun for long periods of time, or stay in the cold for too long.[15]Marsupials are born hairless and grow out fur later in development.
Humans are the onlyprimate species that have undergone significant hair loss. The hairlessness of humans compared to related species may be due to loss of functionality in thepseudogene KRTHAP1 (which helps producekeratin)[16] Although the researchers dated the mutation to 240,000 years ago, both theAltaiNeandertal andDenisovan peoples possessed the loss-of-function mutation, indicating it is much older. Mutations in the geneHR can lead tocomplete hair loss, though this is not typical in humans.[17]
At times, when a hairless domesticated animal is discovered, usually owing to a naturally occurring genetic mutation, humans may intentionally inbreed those hairless individuals and, after multiple generations, artificially create hairless breeds. There are several breeds of hairless cats, perhaps the most commonly known being theSphynx cat. Similarly, there are some breeds ofhairless dogs. Other examples of artificially selected hairless animals include thehairless guinea-pig,nude mouse, and thehairless rat.
Fur has long served as a source of clothing for humans, includingNeanderthals. Historically, it was worn for its insulating quality, with aesthetics becoming a factor over time. Pelts were worn in or out, depending on their characteristics and desired use. Today fur and trim used in garments may be dyed bright colors or to mimic exotic animal patterns, or shorn close likevelvet. The term "a fur" may connote a coat, wrap, or shawl.
The manufacturing of fur clothing involves obtaining animal pelts where the hair is left on the animal's processed skin. In contrast, makingleather involves removing the hair from the hide or pelt and using only the skin.
^abDawson, T. J.; Webster, K. N.; Maloney, S. K. (2014). "The fur of mammals in exposed environments; do crypsis and thermal needs necessarily conflict? The polar bear and marsupial koala compared".Journal of Comparative Physiology B.184 (2):273–284.doi:10.1007/s00360-013-0794-8.PMID24366474.S2CID9481486.
^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.PMID11214905.S2CID21545865.
