The figure shows ethnic grouping and localities of study participants, KB1, NB1, TK1, MD8 and ABT (a–e, respectively), areas of arid and desert climates and the geographic distribution of the Khoisan and Niger–Congo languages30. The Khoisan languages are characterized by clicks, denoting additional consonants. The ! is a palatal click; / is a dental click; and # is an alveolar click26. Note that the ABT Y chromosome haplogroup was determined using both genotyping and sequencing data generated by this study.