Exposed to the harshest conditions imaginable on the unforgiving Iberian tundra, desperate early humans may have had no choice but to retreat into caves and hibernate. In this dark and cold environment, they may have lapsed into “metabolic states that helped them survive for long periods of time in frigid conditions with limited supplies of food and enough stores of body fat,” Arguaga and Bartsiokas explained. The researchers acknowledge that their speculative hypothesis sounds like “science fiction.” But they note that primitive primates, from which we all evolved directly or in parallel, are among the animals known to have hibernated. This suggests that “the genetic basis and physiology for such a hypometabolism could be preserved in many mammalian species, including humans.”