Bear envy: Why can’t we hibernate, too?
It’s “lights out” for bears in North America. They’re fat. They’re happy. Wake them when the weather gets better.
Humans struggling for a respectable eight hours of sleep may look upon the genus Ursus with envy and ask, “Why can’t we pass out for a few dark months?”
Black bears sleep so soundly that mamas can give birth without even waking up. The cubs manage to find a nipple and stay attached until spring flashes the green light and the family resumes activity.
Hibernation is essential to some animals’ survival. It slows down their breathing and heart rate and sends body temperature lower — all useful in months when food is scarce. And it keeps the animals hidden from predators at a time when they might be out and about scavenging for food.
Bears apparently sleep longer (up to seven months) in places like Arizona than they do in New York. That’s because the northern bears have extended access to nuts and berries.
Bears hibernate in their dens, but several years ago, a 500-pound black bear chose a basement in Hopatcong, New Jersey. In preparation, he had brought twigs and leaves downstairs. The bear was discovered by a very surprised cable guy.
Many other animals hibernate. Bats hibernate in caves (or your attic). Hedgehogs prefer their nests.
Dormice go underground, with some hibernating as long as 11.4 months, nearly a whole year. In Europe, it’s a question of the beeches’ ability to provide seeds. Dormice need these seeds to reproduce. So when they are in short supply, the animals skip reproduction and survive by staying hidden.
Some hibernation occurs in warm weather. Large white butterflies in Spain “sleep” all summer to avoid the wasps that would destroy their eggs.
Back to the primary question: Why don’t humans hibernate?
First off, humans evolved in tropical Africa, where year-round food supply was abundant and temperatures never approached freezing. Human hearts stop at a body temperature of 82 degrees, Thomas Ruf of the University of Veterinary Medicine in Vienna, explained to the BBC. Bear hearts evolved to continue beating at a body temperature of 34 degrees.
Humans don’t have to hide from predators, because we’re the predators. And we don’t need firearms to kill a bear. We can do it with a car alarm. Waking up from hibernation requires an enormous amount of energy, so a bear roused too early by a car alarm might lack the reserves to survive the rest of the winter.
Humans are primates, and some primates — certain lemurs and lorises — already hibernate. That leaves hope that one day, humans can be engineered to hibernate.
This would be especially helpful for space travel. Hibernating astronauts would not need a lot of supplies to stay alive, explains Rob Henning, a University of Groningen (in the Netherlands) anesthesiologist working with NASA.
Also, hibernators don’t experience massive loss of muscle or bone during their torpor. Astronauts in space currently have to exercise a tedious six hours a day just to maintain body strength.
A serious drawback to hibernation is memory loss. After emerging from hibernation, squirrels that had previously mastered a maze at the Vienna veterinary school knew not where to turn.
“It might be that we can put astronauts into hibernation,” Ruf says, “but when they wake up, they might not know who they are or what to do.”
Science is working on it.
In the meantime, humans living in harsh climates will continue applying their ingenuity to getting through winter while staying conscious. Those choosing the easy way out may do not as the bears do but as the birds do and fly south.