By Donald E. Moore III, PhD, Smithsonian’s National Zoo and Conservation Biology Institute
Animal hair is important to mammals’ survival: They use its form and color patterns for displays and camouflage, for its insulating properties, for self-defense, and even as a sensory organ. But what are the other properties that make this fuzzy collection of chemicals so unique to the animal kingdom?
What is Animal Hair?
The technical definition of “hair” is “a filament made of keratin protein that grows from follicles in the skin.” Keratin is a major structural protein in all vertebrates, found in skin, claws, hooves, and nails, as well as in hair. Although animal hair seems delicate to us, keratin protein is one of the toughest proteins an animal can produce. Hair is unique to mammals; although many groups of animals produce keratin, only mammals turn that keratin into hair.
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Why Animal Hair Matters
Hair is important to mammals for several reasons. They use its form and color patterns for displays and camouflage; they use it for its insulating properties, for self-defense, and even as a sensory organ.
This is a transcript from the video series Zoology: Understanding the Animal World. Watch it now, on Wondrium.
We don’t know when hair evolved, because it is rare in the fossil record. But zoologists do think that hair coincides with the evolution of warm-bloodedness or “endothermy”, the ability to produce our own body heat, because hair is a good insulator. If you spend a lot of metabolic energy producing body heat, it is most efficient to retain it rather than lose it to the environment around you.
The Amazing Arctic Fox Hair
Unsurprisingly, arctic animals have a lot of hair for insulation against the cold. For example, zoologists have estimated that the Arctic fox has tens of thousands of hairs per square inch; that’s a lot more than humans have! With a deep underfur and plentiful guard hairs on the outside, the small, nonmigratory Arctic fox may be the best-adapted of all Arctic creatures for cold temperatures down to forty-below-zero or lower.
Other Arctic animals, like polar bears and caribou, have thick coats of hollow hairs—these insulate like our winter parkas stuffed with synthetic hollow-fiber filling for efficient protection against the deep cold.
Arctic foxes also use their fur for camouflage. They are the only members of the Canidae family—dog-like carnivores—whose fur changes color with the seasons. In the winter, it turns pure white to blend in with the snow of its tundra habitat.
For summer, it sheds its white fur and replaces it with a brownish or grayish coat that blends in with the tundra grasses. This is useful, as the Arctic fox sits in the middle of the food chain. It preys on small animals like rodents and fish, and in turn, it is preyed on by wolves and bears. Its seasonal coloring disguises it from both predators and prey.
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Animal Hair Markings
Other times, an animal may use its fur for the opposite purpose: To be better seen. The classic example is the lion. Lions are the only members of the Felidae family—cat-like carnivores—that have visible sexual dimorphism. In other words, there’s an obvious visual difference between males and females: Male lions have manes.
The mane is not just a signal of male-ness. The color and size of a lion’s mane are influenced by its sex hormones, including testosterone. Research indicates that lions with darker, thicker manes have higher testosterone levels, and not only that, lionesses prefer males with big, dark manes. A mane gives the lioness information about a lion’s ability to survive and reproduce.
Hairless Mammals Still Have Hair
Hair is unique to mammals, and all mammals have some form of hair. But wait a minute, dolphins and whales are mammals and they’re hairless! But in fact, although they look hairless they do have a few small, whiskery hairs on their chins.
Elephants look hairless from a distance, but in fact, they do have hair, which is more obvious in juveniles than adults. Baby elephants are often redheads, with sparse but easy to spot hair on their heads and backs. Adult elephants have much less hair, but it is coarse and black, easiest to spot on the tips of their tails.
Hair takes on many forms that might surprise you. Many mammals have defensive structures made entirely of hair. Porcupines may be the most famous example. All porcupine species are slow and lumbering, which might make them vulnerable to a faster predator. But to make up for their lack of speed and agility, they have strong, barbed quills that are enlarged, modified hairs. These quills are very painful and difficult to remove, so most predators learn quickly to avoid porcupines.
Similarly, the spiny covering of hedgehogs and the horns of rhinoceros are made of keratin, the same substance that hair is made of. Modern research has busted the old myth that rhino horn is just a clump of dense hair. CT scans and other analyses show that the rhino’s horn covering is more like a horse hoof than like Rapunzel’s long hair. Note that rhinos also have hairs on the outside of their bodies like other mammals.
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Are Whiskers Hair?
Specialized whiskers on cats, dogs, and other mammals are also modified hairs. Whiskers are technically called “vibrissae,” and they work as sensory receptors. Cats and mice use these sensitive whiskers in the same way we use our fingertips to feel our way around in the dark, to find one another, or to avoid enemies.
There is a sensory organ at the base of the whisker called a proprioceptor, which sends tactile signals to the nervous system and brain. The proprioceptor relates the position of the body and limbs or head, which is important for an animal to be able to make quick decisions for the next movement. They can help an animal figure out if it can fit into a tight space, and can even sense air movements which probably helps running predators respond to changes in prey movement.
Some domestic animals have long whiskers, curly whiskers, or whiskers in strange places like the upper lip, chins, or even ears. Some people feel that they should trim these whiskers. But without these specialized sensory hairs, the animals can become disoriented, frightened, and stressed; animal whiskers therefore should be left intact.
What is the Difference Between Human Hair and Animal Hair?
Even though both human and animal hair is made of the same proteins, there are enough differences that allow them to be differentiated from each other. For instance, the cuticle—the outermost layer of hair—tends to have different patterns in animals than in humans. The innermost layer of hair in animals—the medulla— also tends to be thicker on animals, especially species that need to stay warm in colder climates.
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In both animal and human hair, melanin is found in the cortex layer and provides hair with its specific color. Unlike animals, human hair tends to be consistent in coloration from root to tip, where animal hair tends to change in melanin density along the length. This change in coloring is referred to as “banding”.
Common Questions About Animal Hair
There are many scientific differences between human and animal hair, including the fact that animal hair has denser pigmentation and can change in patterns such as bands, while human hair cannot.
Animal hair is used in many products. Horse hair is used for stringed instrument bows as well as brushes. Ox hair, hog bristle, and Siberian weasel hair are all used in making paint brushes as well.
As a horse is a mammal and all mammals have hair, horses are considered to have hair. It is animal hair and thus different from human hair.