Animals Wildlife 9 Nearly Hairless Mammals By Bryan Nelson Writer SUNY Oswego University of Houston Bryan Nelson is a science writer and award-winning documentary filmmaker with over a decade of experience covering technology, astronomy, medicine, and more. our editorial process Twitter Twitter Bryan Nelson Updated May 31, 2017 Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species 1 of 10 Show Some Skin Photo: Asichka/Shutterstock All mammals have hair — it is one of their defining biological characteristics — but there are a few bizarre species with hair so reduced by evolution that they actually appear to be naked. Perhaps it's because of the essential nature of this mammalian trait that we find bare skin such a strange and comical thing on a mammal. Before poking fun at these adorable little nudies, however, don't forget to look in the mirror. We humans are among them. 2 of 10 Cetaceans Photo: ahudson216/Shutterstock Cetaceans — or the whales, dolphins and porpoises — are the largest group of hairless mammals, and for good reason: Hair doesn't make a lot of sense given their aquatic lifestyles. They have opted instead to insulate themselves with a thick layer of blubber. Although all cetaceans exhibit hair on their heads as fetuses, hair is eventually lost except for in a few species, such as with the bowhead whale, which has hairs on its lips, chin, snout and behind its blowhole. 3 of 10 African Elephant Photo: Villiers Steyn/Shutterstock The relative hairlessness of the world's largest living land mammal is an adaptation to the dry, hot climate. With such large bodies, dissipating heat is more important to elephants than retaining it. As they grow in size, elephants lose more and more hair. 4 of 10 Walrus Photo: Vladimir Melnik/Shutterstock Hair is used as an insulator for many mammals, but walruses, like a number of other semi-aquatic mammals, have forsaken this trait and replaced it with a cushy layer of subcutaneous fat. Walrus blubber is so thick that fur has become almost entirely unnecessary, and if it wasn't for their characteristic whiskers, their bodies would appear completely naked. 5 of 10 Hairless Dogs Photo: Vladimirkarp/Shutterstock There are four recognized breeds of hairless dog today: the Chinese crested dog, the Mexican hairless dog, the American hairless terrier and the Peruvian hairless dog (pictured). But there are several other varieties of hairless dogs that have yet to be officially recognized. They might be hairless, but they still enjoy a good rub as much as the next dog, and they're perfect for pet owners with allergies. 6 of 10 Sphynx Photo: Natalie magic/Shutterstock Depending on whom you ask, a Sphynx is either distinctive and adorable, or creepy and chupacabra-like. These are the hairless cats, shaped by breeders rather than evolution, but still quite comfortable in their own skin. To the uninitiated, their hairlessness might take some getting used to, but they're still just cats on the inside. Sphynxes are known for their extroverted personalities, displaying high levels of energy, curiosity and affection. And the good news for pet owners? No hairballs! 7 of 10 Skinny Pig Photo: Julia Kaysa/Shutterstock Skinny pigs are the name given to a breed of hairless guinea pigs. They were originally bred in a lab, primarily for use in dermatology studies, but have since become part of the pet population. Skinnies are distinctive for their human-like skin, which could be either comforting or creepy. 8 of 10 Naked Mole Rat Photo: belizar/Shutterstock Nudity might be the least bizarre trait of these oddball rodents. Unlike most mammals, naked mole rats don't regulate their own body temperature and don't have any pain receptors in their skin, likely an adaptation to their burrowing lifestyle. They are also the only known eusocial mammals, meaning their social structure closely resembles that of insects like ants or bees. 9 of 10 Babirusa Photo: Vladimir Wrangel/Shutterstock These bizarre, mostly hairless animals are members of the pig family found in Indonesia. Babirusa are so strange-looking that some Indonesian locals have taken to creating demonic masks inspired by the animals. Aside from their bare skin, they are also distinctive for their backward-curving tusks, which can grow long enough to penetrate their skulls if the animal fails to grind them down. 10 of 10 Hippopotamus Photo: Volodymyr Burdiak/Shutterstock 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. Interestingly, despite looking like they might be related to pigs and other terrestrial even-toed ungulates, hippos are actually most closely related to modern-day cetaceans. So hairlessness seems to run in the family!