The parenting instinct can be so strong in animals that sometimes it overpowers the predatory instinct, resulting in unusual relationships between members of different species.
Here's a collection of videos that document some very unexpected examples.
In Ireland, a farmer took several duck eggs to his barn and left them there to hatch. He discovered that a mother cat, instead of attacking or devouring them, had adopted the hatched ducklings and was raising them as part of her own kitten litter.
What's just as amazing is that the ducklings learned how to suckle, since ducks don't breastfeed.
Here's more footage of the cat (hilariously) trying to rein in the ducklings, who were outgrowing their kitten siblings and becoming quite a pawful to handle.
Here's the reverse situation in which a male duck adopted several orphaned kittens, proving that even male animals have the parenting instinct.
This mother cat adopted a baby squirrel as part of its litter.
Incredibly, the little squirrel even learned how to purr, believe it or not.
In this strange case, while birds and cats are traditional enemies, a wild crow took to taking care of an abandoned kitten, even ensuring it was fed.
Closer to home, on Vancouver Island, just outside Courtenay, B.C., a dog adopted an abandoned fawn.
The pair became an internet sensation that resulted in news coverage, videos, a website, and even a book.
Here's the full BBC documentary Animal Odd Couples, that takes a look at interspecies relationships that span the range from friendships to even, yes, attraction (speaking of which, you may have heard about a zonkey recently born to a donkey and zebra).
Perhaps we humans can learn a thing or two from these animals about overlooking differences and focusing on the important things in life?