What we don't know about great ape variation.

The patterning of intraspecific variation among the great apes is proving more complex than has been recognized previously. The great ape species, as currently defined, may include markedly different subspecies, alternatively, the majority of intraspeclflc variation may be observed at the populational level within a single subspecies. Recent studies have raised a number of questions about great ape evolutionary biology. How many species of living great apes exist? What was the original dietary adaptation of gorillas? How should we define male orang-utan adulthood?