Made famous by the movie March of the Penguins, emperor penguin fathers endure below-freezing temperatures and forgo food to incubate their eggs.

After the female lays a single egg, her mate rests it on his feet and covers it with a flap of skin (above, a penguin protects its chick using the same skin flap).

"You could think of that pouch as almost a male womb, except they're birds," the University of Reading's Pagel said. "They're very much like seahorses in that respect: [They've] taken over a role rightly or wrongly we traditionally associate with females."

For four months the males huddle together, not moving much, while the females fill up on seafood in the ocean. The females eventually return to help feed the newly hatched chicks.

Both Pagel and Forbes say that animal parents give us insight into how human families work. "We can see ourselves in other animals," Pagel said.