9 Nearly Hairless Mammals

All mammals have hair, but sometimes they've evolved to appear naked.

mom hipppo with newborn baby by river

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All mammals have hair. It is one of their defining biological characteristics. However, there are a few species with hair so reduced by evolution that they actually appear to be naked.

Perhaps it is because of the essential nature of this mammalian trait that we find skin on a mammal that appears bare to be such a strange sight. And yet, the idea should be more familiar to us than it is because humans are among the most hairless of all mammals. We've been called "the naked apes of the world."

From aquatic creatures to popular household pets, here are nine nearly hairless mammals.

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blue dolphin smiles while stalling upright in water

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Cetaceans are the largest group of hairless mammals, made up of animals including whales, dolphins, and porpoises. This makes sense, as hair isn't very helpful for an aquatic lifestyle. Instead, these creatures insulate themselves with a thick layer of blubber.

Although all cetaceans exhibit hair on their heads as fetuses, it is eventually lost. Baby dolphins have whiskers in utero, but shed them after birth. A few species are exceptions to this; one example is the bowhead whale, which has hairs on its lips, chin, and snout, and behind its blowhole.

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African Elephant

line of African elephants drinking in watering hole

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The African elephant is the world's largest land mammal, and it's also nearly hairless. This is because of an adaptation to the hot, dry climate in which it lives. With such large bodies, dissipating heat is more important to elephants than retaining it, which hair usually facilitates. As they grow in size, elephants lose more and more hair.

What little hair elephants do have is noticeably thin, in terms of hair shaft diameter. This, researchers suspect, could be good at wicking heat away from the body. "Thick hair traps air and keeps the body warm. But below a certain density, hair stops insulating and wicks heat off the body instead—helping the elephants get rid of an extra 20% of their body heat, especially on windless days."

It is also possible that hair on African elephants used to have sensory or protective purposes. While that is no longer the case—except for possibly an elephant's trunk—the continued presence of hair may be residual from evolution.

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group of walruses huddled on beach with long tusks

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Hair is used as an insulator for many mammals, but walruses, like a number of other semi-aquatic mammals, have minimalized this trait and replaced it with a layer of subcutaneous fat. Walrus blubber is so thick that hair is almost entirely unnecessary, but the animal is nonetheless covered in short, reddish-brown fur that gives these animals their cinnamon color. This coat is barely noticeable, however, so if it wasn't for their characteristic whiskers, walrus' bodies would appear completely naked.

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Hairless Dogs

hairless dog with big ears sits on black and white pillow

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There are a number of hairless dog breeds out there, including the Chinese crested dog, the Mexican hairless dog, the American hairless terrier, and the Peruvian hairless dog (pictured above). But there are several other varieties of hairless dogs that have yet to be officially recognized.

Hairless dogs are popular pets because they are both hypoallergenic and convenient—there's no shedding to worry about. However, their lack of hair does mean that they need sunscreen in hot weather and jackets for warmth in the cold, so they're high-maintenance in other ways.

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hairless sphynx cat lays down and glares

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Depending on who you ask, a Sphynx is either distinctive and adorable or ugly and creepy. This animal is not to be confused with a sphinx, the mythical creature with the head of a human and body of a lion after which the massive statue in Giza was modeled. Instead, these are hairless cats shaped by breeders—not mythology or evolution.

Of course, since Sphynx cats are mammals, they are not completely hairless. They are covered in fine, barely noticeable down that contributes to the soft feel of their skin.

Despite their untraditional looks, Sphynxes are well-loved as pets. They are known for their extroverted personalities, high energy levels, curiosity, and affection. Plus, like hairless dog breeds, there is no shedding to worry about.

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Skinny Pig

hairless guinea pig sniffs small fruit

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"Skinny pig" is the name given to a breed of hairless guinea pigs. They do not differ much from the standard guinea pig you are familiar with except for the fact that they are nearly hairless and you're looking right at their folds of skin (which come in many different colors). The small bit of fur they do have is found on their legs, feet, and muzzles.

Their name is given not because they are actually skinnier than regular guinea pigs but because of the exposed nature of their skin. They were originally bred in a lab—primarily for use in dermatology studies, where they can still be found, sadly—but have since become part of the pet population. Their defective hair shafts are due to a genetic mutation.

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Naked Mole-Rat

naked mole-rat looks out from round hole

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True to its name, the naked mole-rat is another nearly hairless mammal. It is identified by its wrinkly, pinkish-gray, slightly translucent skin.

The naked mole-rat is the only mammal that does not regulate its own body temperature—it simply adopts the temperature that surrounds it. They also do not have pain receptors in their skin; it has been suggested that this is an adaptation to their burrowing lifestyle and the subsequent overexposure to carbon dioxide.

Naked mole-rats are the only known eusocial mammals, meaning their social structure closely resembles that of insects like ants or bees.

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profile of babirusa walking in water

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Also called deer-pigs (which is the English translation of their Malay name), these mostly hairless animals are members of the pig family and are found in Indonesia. Aside from their nearly bare skin, babirusa are distinctive for their dual pairs of teeth, specifically the upper pair that appears to be growing out of its snout. These are backward-curving and can grow long enough to penetrate the skull if the animal fails to grind them down. These animals can weigh over 200 pounds at full size.

Babirusa are so strange-looking that some Indonesian locals have taken to creating demonic masks inspired by the animals.

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mother and baby hippo walk along dirt ground

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Hippos lack hair for much the same reason that other aquatic and semi-aquatic mammals do; fat is a more useful insulator for large animals that spend most of their time in the water. This lack of hair does leave hippos vulnerable to the sun, however, so they secrete a light-absorbing substance that acts as a kind of natural sunscreen. They need this, since they lack the glands that produce an oily substance called sebum that other mammals rely on for skin lubrication.

Interestingly, despite looking like they might be related to pigs and other even-toed ungulates, hippos are actually most closely related to modern-day cetaceans.