Some bees go out foraging, but one stands by the entrance to the nest.

Think about an animal. It has to get food, but at the same time it has to protect itself from predators.

The division of labor between men and women - men gather 68 percent of the calories in foraging societies - requires cooperation between the sexes.

"Whales, on the other hand, often feed at depth, " says Roman. "So they feed low in the water column.

The truth was that polar bears are ferocious wild animals and can become desperate for food in the ice-free summer months.