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. Although many animals use simple tools, only human beings, whose use of stone tools dates back hundreds of millennia, have been observed using tools to make other tools. Early human tools, made of such materials as stone, bone, and wood, were used for preparation of food, hunting, manufacture of weapons, and working of materials to produce clothing and useful artifacts. The development of metalworking made additional types of tools possible. Harnessing energy sources, such as animal power, wind, or steam, allowed increasingly complex tools to produce an even larger range of items, with the Industrial Revolution marking an inflection point in the use of tools. The introduction of widespread automation in the 19th and 20th centuries allowed tools to operate with minimal human supervision, further increasing the productivity of human labor. By extension, concepts which support systematic or investigative thought are often referred to as "tools" or as "toolkits". Definition While a common-sense understanding of the meaning of tool is widespread, several formal definitions have been proposed. In 1981, Benjamin Beck published a widely used definition of tool use. This has been modified to:Other, briefer definitions have been proposed: History Anthropologists believe that the use of tools was an important step in the evolution of mankind. Because tools are used extensively by both humans (Homo sapiens) and wild chimpanzees, it is widely assumed that the first routine use of tools took place prior to the divergence between the two ape species. These early tools, however, were likely made of perishable materials such as sticks, or consisted of unmodified stones that cannot be distinguished from other stones as tools. Stone artifacts date back to about 2.5 million years ago. However, a 2010 study suggests the hominin species Australopithecus afarensis ate meat by carving animal carcasses with stone implements. This finding pushes back the earliest known use of stone tools among hominins to about 3.4 million years ago. Finds of actual tools date back at least 2.6 million years in Ethiopia. One of the earliest distinguishable stone tool forms is the hand axe. Up until recently, weapons found in digs were the only tools of "early man" that were studied and given importance. Now, more tools are recognized as culturally and historically relevant. As well as hunting,