Naked mole-rat

The naked mole-rat, sometimes called the sand puppy, is a rodent that lives in burrows across the Horn of Africa and parts of Kenya, especially in Somali areas. It belongs to its own genus, *Heterocephalus*, and its closest relatives are blesmols. This animal stands out for being the only mammal that regulates its body temperature like a cold-blooded creature—it lets its body temperature match the surrounding environment. It also lives in a eusocial system, meaning it has a strict social structure with a breeding queen, non-breeding workers, and shared care of the young. Only one other mammal, the Damaraland mole-rat, shares this eusocial arrangement. Naked mole-rats feel no pain in their skin, have unusually slow metabolisms and breathing rates, live a very long time, and show strong resistance to cancer and low-oxygen conditions. Although scientists once grouped them with other African mole-rats in the family Bathyergidae, newer research places them in their own family, Heterocephalidae.

A typical naked mole-rat measures 8 to 10 centimeters long and weighs 30 to 35 grams, though breeding females are larger, often exceeding 50 grams and sometimes reaching 80 grams. Their bodies are built for life underground. Their tiny eyes give them poor vision, and their short, thin legs let them move just as fast backward as forward. They dig with large, protruding teeth, and their lips close behind those teeth to keep dirt out of their mouths. About a quarter of their muscle power goes into closing their jaws while digging. They have almost no hair—hence the name—and their wrinkled skin is pink or yellowish, lacking any insulating layer.

In their oxygen-poor tunnels, naked mole-rats have adapted well. Their lungs are underdeveloped, and their hemoglobin grabs oxygen very efficiently, so they use oxygen sparingly. Their resting metabolism is about 70% that of a mouse, and during long periods without food, they can cut that rate by another 25%. They can survive at least five hours in air with only 5% oxygen, showing no distress, and they can handle an atmosphere of 80% carbon dioxide mixed with 20% oxygen. In a completely oxygen-free environment, they last 18 minutes without apparent harm—though none survived 30 minutes. During such anoxia, they lose consciousness, their heart rate drops from about 200 to 50 beats per minute, and breathing nearly stops. Instead of usin