In the physical adaptation view, one function (producing speech sounds) must havebeen superimposed on existing anatomical features (teeth, lips) previously used forother purposes (chewing, sucking). A similar development is believed to have takenplace with human hands and some believe that manual gestures may have been aprecursor of language. By about two million years ago, there is evidence that humanshad developed preferential right-handedness and had become capable of makingstone tools. Wood tools and composite tools eventually followed. Tool-making, or theoutcome of manipulating objects and changing them using both hands, is evidence ofa brain at work.