He compared bones and muscles of human and chimpanzee thumbs , finding that humans have 3 muscles which are lacking in chimpanzees .
In 1994 , Randall Susman used the anatomy of opposable thumbs as the basis for his argument that both the Homo and Paranthropus species were toolmakers .
Randall Susman compared bones and muscles of human and chimpanzee thumbs , finding that humans have 3 muscles which are lacking in chimpanzees .
In 1994 , Randall Susman used the anatomy of opposable thumbs as the basis for his argument that both the Homo and Paranthropus species were toolmakers .