Hominization in the rainforest: The chimpanzee's piece of the puzzle

Many models of human evolution propose that key behavioral innovations were involved in the divergence of the human line from the ape line. An ecological reason, the shift from dense forests to a more open habitat, is suggested as the basis for these innovations. Primate models can be useful to our understanding of how environmental factors can affect such key behaviors. New results on forest chimpanzees demonstrate that for most patterns of behavior considered to favor a savanna model, the environmental influences are in opposition to the expectations. A new evaluation of the environmental influences on human evolution is required. We propose that either patterns of key human behaviors were inaccurately distinguished or that the hominization process started while the common ancestor of the chimpanzee and man was alive.