50,000 and 46,000 years ago. This date fits quite well with the theory that behaviorally modern humans were able to leave Africa only 50,000 years ago.
As for the barbed points and other artifacts, Klein argues that they are, at least for the moment, anomalies that don't fit into the established archaeological pattern. If the Katanda points are 100,000 years old, why didn't such an important technique as fishing spread like wildfire? Yet no other African site shows evidence of fishing until 25,000 years ago. Klein, who does his fieldwork in Africa, has twice found sheep bones in strata belonging to the Middle Stone Age, which ended 50,000 years ago. Since sheep were not domesticated for another 40,000 years, the bones are clearly intrusions from a higher level, introduced by burrowing animals or one of the many other sources of confusion in the archeological record. Archaeologists must expect to find a few later intrusions in any stratum, Klein believes, and should therefore base their conclusions on well established patterns, not on the occasional anomaly. His critics, he believes, are looking at the noise in the record, not its true signal. Looking at the extraordinary process by which apes were slowly molded into humans, it is easy to think of the end result as some goal that evolution was driving toward. But evolution, of course, is a blind, inanimate process with no goals, let alone any interest in human welfare. It is driven by mutation, natural selection and drift. Mutation—random natural changes in the chemical units of DNA—is the ceaseless generator of novelty in the human genome. That novelty is the raw material on which natural selection acts, rejecting changes for the worse and retaining those that confer reproductive advantage. The mighty tide of genetic drift, through the random selection of genes between generations, makes some genetic variants a permanent fixture in a population and extinguishes many others, reducing the novelties that mutation introduces. The interplay of these three forces may sound like a recipe for chaos, yet evolution's mechanisms do in fact bring into being, over the course of long periods of time, structures of extraordinary complexity, such as the human ear or eye. Because such adaptations are ones that human engineers could create only by design, biologists often talk about evolution as if it possessed intent or forethought. But this is just a shorthand way of referring to the evolutionary process and is not meant to imply that evolution has any goal in mind.
In the sense of the biologists' shorthand, it could be said that with the development of language, evolution had accomplished a major part of the task of morphing an ape into a human, and of shaping humans into a truly social species. Since language is such a defining faculty of modern humans, providing perhaps the only clear distinction between people and other species, its nature and evolution merit a closer look.
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