A common trend in size differences between males and females is a long-standing puzzle. A study of shorebirds shows that the type and strength of competition for mates may explain much of the pattern.

Animal intelligence varies widely. Some have cognitive abilities that were once thought to be limited to humans, while others seem to act purely on instinct. It’s not simply a matter of having large ...

Behavior that we’d consider intelligent is oddly widespread in the animal kingdom. Animals with very different brains from ours—a species of octopus and various birds—engage with tools, to give just ...

The relative size of the human male's penis and testes can be reduced to our species' mating strategies, and can provide some surprising insights into early human culture. Humans have a much longer ...