title: African Y chromosome and mtDNA divergence provides insight into the history of click languages.
abstract: BACKGROUND
  About 30 languages of southern Africa, spoken by Khwe and San, are characterized by a repertoire of click consonants and phonetic accompaniments. The Jumid R:'hoansi (!Kung) San carry multiple deeply coalescing gene lineages. The deep genetic diversity of the San parallels the diversity among the languages they speak. Intriguingly, the language of the Hadzabe of eastern Africa, although not closely related to any other language, shares click consonants and accompaniments with languages of Khwe and San.
  
  
  RESULTS
  We present original Y chromosome and mtDNA variation of Hadzabe and other ethnic groups of Tanzania and Y chromosome variation of San and peoples of the central African forests: Biaka, Mbuti, and Lisongo. In the context of comparable published data for other African populations, analyses of each of these independently inherited DNA segments indicate that click-speaking Hadzabe and Jumid R:'hoansi are separated by genetic distance as great or greater than that between any other pair of African populations. Phylogenetic tree topology indicates a basal separation of the ancient ancestors of these click-speaking peoples. That genetic divergence does not appear to be the result of recent gene flow from neighboring groups.
  
  
  CONCLUSIONS
  The deep genetic divergence among click-speaking peoples of Africa and mounting linguistic evidence suggest that click consonants date to early in the history of modern humans. At least two explanations remain viable. Clicks may have persisted for tens of thousands of years, independently in multiple populations, as a neutral trait. Alternatively, clicks may have been retained, because they confer an advantage during hunting in certain environments.
authors.affiliation: Department of Anthropological Sciences, Stanford University, Stanford, CA 94305, USA. aknight@stanford.edu
authors.forename: Alec
authors.initials: A
authors.lastname: Knight
authors.forename: Peter A
authors.initials: PA
authors.lastname: Underhill
authors.forename: Holly M
authors.initials: HM
authors.lastname: Mortensen
authors.forename: Lev A
authors.initials: LA
authors.lastname: Zhivotovsky
authors.forename: Alice A
authors.initials: AA
authors.lastname: Lin
authors.forename: Brenna M
authors.initials: BM
authors.lastname: Henn
authors.forename: Dorothy
authors.initials: D
authors.lastname: Louis
authors.forename: Merritt
authors.initials: M
authors.lastname: Ruhlen
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Mountain
mesh_terms: D000351:Africa, Eastern; D000353:Africa, Southern; D005075:Biological Evolution; D044383:Black People / Q000235:genetics*; D041322:Chromosomes, Human, Y / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics*; D005006:Ethnicity / Q000235:genetics*; D014644:Genetic Variation / Q000235:genetics*; D006801:Humans; D007802:Language; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010802:Phylogeny; D013997:Time Factors
chemical_list: D004272:DNA, Mitochondrial