most complex in the world.
About 30 different click languages are still spoken in southern Africa. They fall into three groups that, apart from their clicks, bear little evident relationship to each other. Speakers of another two click languages, known as Hadza and Sandawe, live far away in Tanzania. Hadza and Sandawe are both isolates, meaning they have no known relationship to each other or to the !Kung language of the San. Despite the fact that many of the click languages apparently have nothing in common save their clicks, Joseph Greenberg, the great classifier of the world's languages, assigned them all to a single family, known as Khoisan. Linguists grumbled that it was illogical to define a group of unrelated languages as a family, but went along with the idea because no one knew what else to do with the click languages. Greenberg is at present reviled by most historical linguists, but his classification of the Khoisan languages seems a stroke of genius in light of a surprising new link that has now emerged among them. The link is the finding from genetics that the Hadza speakers and the !Kung are two of the most ancient populations in the world. All peoples are of course the same age in the sense that everyone is descended from the ancestral human population. But some populations are viewed as older than others because they lie on longer branches of the human family tree. In a recent survey of African populations, Douglas Wallace of the University of California at Irvine found that three of the most ancient peoples in the world were the Biaka pygmies of the Central African Republic, the Mbuti pygmies of the Congo, and the !Kung San. The !Kung possess several lineages of mitochondrial DNA, Wallace and his colleagues found, but their principal lineage forms the first branch of L1, the oldest of the three divisions of the human mitochondrial tree. This lineage, Wallace notes, "is positioned at the deepest root of the African phylogenetic tree, suggesting that the
!Kung San became differentiated very early during human radiation."_
In other words, the !Kung San split off from the ancestral population at an early date, and have remained a reasonably distinct population ever since.
Two Stanford researchers, Alec Knight and Joanna Mountain, recently compared the genetics of the !Kung with that of the Hadzabe, as the speakers of Hadza click language are known, a foraging people who live near Lake Eyasi in Tanzania. They discovered that the Hadzabe too are an extremely ancient people. However, the Hadzabe belong not to the L1 division of the mitochondrial DNA tree but to L2. Because L2 and L1 mark two of the first forks in the tree, the !Kung of L1 and the Hadzabe of L2 are two populations that separated almost at the dawn of human time. The split between the ancestors of the two groups "appears to be among the earliest of human population divergences," the Stanford researchers say. Based on measurements of their Y chromosomes, the two populations are more distant from each other
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