Human hands are unique in their flexibility and grasping capabilities.
A chimp s hands, good for swinging in trees, are virtually useless on the baseball diamond. The flexible joints of our index and pinky fingers allow us to palm a ball and choke up on a bat. Those same joints allowed our ancestors to fashion stone tools and wield clubs. According to one hypothesis, tool-making offered early humans such a competitive advantage that natural selection favored the evolution of our dexterous and versatile hands. But making tools also requires a brain that can think ahead and consider cause and effect.