Some of the theorists who advocate this "revisionist" critique imply that, because the "pure hunter-gatherer" disappeared not long after colonial (or even agricultural) contact began, nothing meaningful can be learned about prehistoric hunter-gatherers from studies of modern ones (Kelly, 24-29; see Wilmsen)

Answer this question, if possible (if impossible, reply "unanswerable"): The "pure hunter-gatherer" appeared not long after what?
unanswerable