08/13/2026
Beary interesting! Could this research lead to more advanced for long space travels?
Black bears enter their dens in November with gunshot wounds, arrow punctures, and infected bite marks from fights with other bears. Five months later they walk out healed. The wounds close. The infections clear. The scars barely form. They do this without eating, without drinking, at a body temperature reduced by 13 degrees Fahrenheit, and in a metabolic state so suppressed that in any other mammal the same conditions would make healing nearly impossible.
Researchers at the Universities of Minnesota and Wyoming discovered the extent of it by accident. While checking on GPS-collared bears in their winter dens as part of a long-term population study, the teams noticed that bears they had documented with significant injuries in the fall were emerging in spring with those injuries resolved.
Gunshot wounds from hunters who had hit but not killed a bear during the fall season. Arrow wounds from bowhunters. Bite wounds from territorial fights with other bears that had been visibly infected and inflamed when the bear entered the den. By the time the researchers opened the den in February or March, the wounds were closed, clean, and showing almost no scar tissue.
David Garshelis, the University of Minnesota bear researcher who had been studying these animals for decades, described his own surprise directly: it seems so remarkable to us that their wounds would heal so well and so completely when they are hibernating and their metabolism is slowed down.
Paul Iaizzo and colleagues designed an experiment to test whether the healing was real or whether the bears had simply recovered during the last warm weeks before denning. They anesthetized hibernating bears inside their dens during early winter, made small full-thickness cuts through the skin, and returned two to three months later to examine the sites.
The wounds had healed completely. New skin had grown over the cuts. New hair follicles had formed at the wound margins. The scar tissue was minimal enough that the researchers described the healing as reduced scar formation, a clinical phrase meaning the bears healed cleaner than a human with full access to food, warmth, and medical care would heal from the same wound.
The paper, published in Integrative Zoology in 2012, laid out why this should not be possible. Even mildly hypothermic body temperatures re**rd healing processes in mammals. A hospital patient whose core temperature drops a few degrees heals slower and develops more infections.
A bear's core temperature during hibernation drops to between 86 and 95 degrees Fahrenheit. Its heart rate falls to roughly eight beats per minute. It does not eat for five to six months. It does not drink. It does not urinate. It does not defecate. It is malnourished, dehydrated, hypothermic, and immobile, every condition that in a human patient would produce the worst possible healing outcome. The bears heal better under those conditions than most mammals heal under the best conditions.
The mechanisms are not fully understood but the pieces are coming together. Bears recycle their own urea, a metabolic waste product that any other mammal would excrete, breaking it back down into nitrogen and using it to synthesize new proteins for tissue repair without consuming food.
Their white blood cell counts increase during hibernation rather than decrease, mounting an immune response that fights infection while the rest of the body operates at minimum power. Their blood carries antimicrobial compounds that appear to prevent wound infection in the absence of any external treatment. They lose almost no muscle mass despite lying motionless for months, and almost no bone density despite bearing no weight on their skeleton for half the year.
Garshelis put it the way it needed to be said: they sit in the den for six months and do not lose any appreciable muscle or bone mass, so this healing is another adaptation. The bear's body does not shut down during hibernation. It redirects. Everything that is not essential stops. Everything that keeps the animal alive and whole when it walks out in April keeps running.
Source: Iaizzo et al. (2012), Integrative Zoology / University of Minnesota / University of Wyoming / BBC Nature / PhysOrg.
