A closer look at one of the hormones known to reduce bone resorption called the cocaine- and amphetamine-regulated transcript showed that it surged to levels 15 times higher than normal in the dozing bears, which suggests that it may play a role in regulating the ways bears have evolved to protect their skeleton from the long periods of stillness.
Polar bears have evolved to survive on the energy-rich, fatty flesh of seals.
This is another handy trick humans have evolved to protect fetuses from toxins their mothers have thrown down their throats things like meatloaf topped with gummy bears.
"Black bears evolved in thickly forested areas and can escape to the top of a tree, so they never really had to defend themselves," said Chris Morgan, a bear ecologist who wrote the just-published "Bears of the Last Frontier" and is featured in a three-part PBS series.
Southey's three bachelor bears evolved into Father, Mother, and Baby Bear over the course of several years.
Polar bears may have already evolved to stay underwater for longer periods, the authors noted.
Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet.
The work also suggests that the bears evolved these changes relatively quickly, likely because they had to adapt to extreme conditions that forced them to switch to a diet that would be toxic to other mammals.
A factor that may help explain the lack of response to non-moving snakes is that bears evolved from canid ancestors that relied on hunting almost exclusively, often in low light conditions, and were dichromats rather than trichromats such as primates that generally have excellent color (wavelength) discrimination (Neitz et al. 1989).
