From double negation to portmanteau

Northern Samo languages of North Western Burkina Faso, belonging to the Mande group of languages, show an extreme variation in all fields of grammar, as in the construction of negation. Double negation marking with a post subject plus a sentence final negation marker was probably a feature of proto Northern Samo. Both markers are extremely variable and prone to loss in some areas. In some areas, double negation marking developed into post subject Portemanteau morphems marking both TAM and negation. Main factors for these variation and developments seem to be very different migration patterns of the subgroups, very different and sometimes assimilated contact groups, and local insecurity in the 18th and 19th century due to slave trade.