Correct me if I'm wrong , but I don't think there's any species in the wild that over eats. It's not in their programming.  "But duh whales and duh walrus and duh bears have lots of fats."  There's a difference between necessity and over eating. They were born that way and through evolution it's a necessity. "But, but I was born this way and muh juhnetics!" No. You were born with your fat parents stuffing your face. This is not nature, it's nurture.