His mother sighs and replies, "Of course you are darling. Your father's a polar bear, I'm a polar bear and all your brothers and sisters are polar bears. This means you can't be anything else."
Not entirely convinced, the baby polar bear seeks his father and asks the same question, "Are you sure I'm a baby polar bear?"
"Of course!" replied Daddy polar bear "we have been polar bears for many generations, my father before me and his before him. All your friends and family are polar bears....why do you ask?"
Spoiler:

