How Evolution Invented Faith: The Patience of the Penguin and the Art of Withstanding Abandonment.

Penguins mate for life and lay one egg per year, which the parents take turns incubating and nursing for long stretches as each ventures into the sea hunting for food. The separation can last for months, during which the starving parent protecting the egg must retain unfaltering faith in the mate’s return — for if they too leave the nursery and go in search of food, the egg will perish.