Gray hair can be bane or beauty, depending on who you ask.

It's also common among primates, leading one reader to inquire via Twitter, "What is the purpose of hair turning gray in primates and humans? Status, lack of status?”

We wonder about that, too—after all, if we make it to the golden years, how come all we get is a head full of silver? (Related: "How Old is That Lion? A Guide to Aging Animals.")

In some species, color denotes ranking—male mandrills with the most brightly colored faces and hindquarters dominate, while lionesses can be more attracted to lions with dark manes, which also have higher testosterone.

But only in one known mammal does gray hair seem