There is an iron law in nature: the larger a species, the longer its members live. That's why whales outlive elephants, and elephants outlive lions. Very few animals defy this rule. Humans have circumvented it thanks to culture. But there is a small animal that laughs in its face. Given its size, the naked mole-rat (Heterocephalus glaber) shouldn't live more than two years, yet they often approach 40. What's more, they age healthily, without typical age-related diseases such as cancer, neurodegenerative disorders, or arthritis.