An Introduction to Human Evolutionary Anatomy . Hamrick, Mark W. and Sandra E. Inouye 1995. Thumbs, tools, and early humans. Hamrick, Mark W., Steven E. Churchill, Daniel Schmitt, and William L. Hylander 1998. Jones-Engel, L.E. and K.A. Bard 1996.
Precision grips in young chimpanzees.
Marzke, M.W. 1986. Tool use and the evolution of hominid hands and bipedality. In J.G. Else and P.C. Lee, eds., Primate Evolution . Marzke, M.W. 1987. Marzke, M.W. 1992.