Editing Nilo-Saharan languages (section)

==Characteristics==
The constituent families of Nilo-Saharan are quite diverse. One characteristic feature is a tripartite [[singulative number|singulative–collective–plurative number system]], which Blench (2010) believes is a result of a [[classifier (linguistics)|noun-classifier]] system in the [[protolanguage]]. The distribution of the families may reflect ancient watercourses in a green Sahara during the [[African humid period]] before the [[4.2-kiloyear event]], when the desert was more habitable than it is today.<ref>{{cite journal |last1=Drake|first1=N. A.|last2=Blench |first2=R. M. |last3=Armitage |first3=S. J. |last4=Bristow |first4=C. S. |last5=White |first5=K. H. |year=2011 |title=Ancient watercourses and biogeography of the Sahara explain the peopling of the desert |journal=Proceedings of the National Academy of Sciences |volume=108 |issue=2 |pages=458–62 |doi=10.1073/pnas.1012231108 |pmid=21187416 |pmc=3021035 |bibcode=2011PNAS..108..458D |doi-access=free }}</ref>