Traditionally, the subgenus of Trypanozoon comprises three socio economically important and highly pathogenic African trypanosomes, i.e., Trypanosoma brucei , T. ev ansi and T. equiperdum . t he relationship of these species has been under much scrutiny over recent years to enable correct diagnosis and detection and to improve our understanding of the genetic and evolutionary relationships. i n this chapter, we have presented the available evidence to help us to unravel these questions with a specific emphasis on understanding the origins of T. evansi and T. equiperdum . We present and evaluate different models of evolution and explore the important question of the potential of these species to become human infective.