An exclusive video of a male polar bear cannibalizing a cub ran on National Geographic last week—the first known instance of the behavior caught on film.  

Tough to watch, we know, but cannibalism has long been known to occur in polar bears during times when seals, their main prey, are hard to find. (See "4 Ways Polar Bears Are Dealing With Climate Change.") 

Weird Animal Question of the Week took the author’s prerogative to ask “Why do animals cannibalize?” 

It isn’t always desperation that drives animal to eat their own. (See "The Flesh-Eaters: 5 Cannibalistic Animals.") 

Take the African lion. Alison Dunn, an evolutionary biologist at the University of Leeds in the U.K., says when a young male lion takes over a pride from an older male, it will kill