A Zoologist Discusses the Science of Animal Hair

From a lecture series: Zoology — Understanding the Animal World

By Donald E. Moore III, Ph.D., Smithsonian’s National Zoo and Conservation Biology Institute

Animal hair is important to mammals for a number of reasons. They use its form and color patterns for displays and for camouflage; they use it for its insulating properties, for self-defense, and even as a sensory organ. But what are some of the other properties that make this fuzzy collection of chemicals so unique to the animal kingdom?

Big male lion lying in dense grassland - Kruger National Park
Lion camouflaged in the prairie grass (Image: Johan Swanepoel/Shutterstock)

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 and in claws, hooves, and nails, as well as in hair. Although animal hair seems very delicate to us, keratin protein is one of the toughest proteins an animal can produce. And 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 a number of reasons. They use its form and color patterns for displays and for 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 The Great Courses Plus.

We don’t really know when hair evolved, because it is rare in the fossil record. But zoologists do think that hair coincides with the evolution of warmbloodedness or “endothermy”, the ability to produce our own body heat, because hair is a very 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

Arctic Fox on a Hill at Omega Park, Montebello, Quebec, Canada
Arctic fox has tens of thousands of hairs per square inch (Image: Fitawoman/Shutterstock)

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 we 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 human winter parkas that have synthetic hollow-fiber filling for efficient protection against deep cold.

Arctic foxes also use their fur for camouflage. They are the only members of the Canidae family—that is, the dog-like carnivores—whose fur changes color with the seasons. In the winter, it is 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 because the Arctic fox sits at 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—the cat-like carnivores—that have visible sexual dimorphism. In other words, there’s an obvious visual difference between males and females—and you know what it is, right? Male lions have manes.

The mane is not just a signal of male-ness. The color and size of a lion’s mane is actually 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! So a mane gives a lioness information about a lion’s ability to survive and reproduce.

Hairless Mammals Still Have Hair

I said earlier that hair is unique to mammals, and I should also add that ALL mammals have SOME form of hair. Now, you may be thinking, 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. It’s easiest to spot on the tips of their tails.

 elephants hair closeup
Adult elephants have much less hair, but it is coarse and black (Image: bypty/Shutterstock)

In fact, 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 really enlarged, modified hairs. And these quills are very painful, and difficult to remove, so most predators learn quickly to avoid porcupines!

In a similar way, 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 rhino 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.

(Image:  Iryna Marienko/Shutterstock)

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 apparently feel that they should trim these whiskers. But without these specialized sensory hairs, the animals can become disoriented, frightened and stressed. So animal whiskers 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 for 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 an animal hair tends to change in melanin density along the length. This is change in coloring is referred to as “banding”.

Common Questions About Animal Hair

Q: What is the difference between human hair and animal hair?

There are many scientific differences between human and animal hair, including the fact that animal hair has much more dense pigmentation and can change in patterns such as bands, while human hair cannot.

Q: Is there any use for animal hair?

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.

Q: Is there hair or fur on horses?

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.

Q: Does cat hair cause harm?

Cat hair itself is not harmful; however, people who are sensitive to cat excretions will have trouble as the cat hair carries those excretions such as dander or saliva which could inflame those with allergies.

This article was updated on 11/29/2019

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