A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task, and proto-typically refers to solid hand-operated non-biological objects with a single broad purpose that lack multiple functions, unlike machines or computers. Although human beings are proportionally most active in using and making tools in the animal kingdom, as use of stone tools dates back hundreds of millennia, and also in using tools to make other tools, many animals have demonstrated tool use in both instances.