Trypanosoma brucei was first seen by David Bruce in 1894, in the blood of a cow in
South Africa, and named in his honour in 1899. Trypanosomes seen in the blood of an
Englishman in The Gambia in 1901 were named T. gambiense in 1902. Finally, in 1909,
trypanosomes from the blood of an Englishman in Zambia ("Rhodesia") were named T.
rhodesiense. Since then there has been continuous debate about the interrelationships
of these three "species". Studies of the molecular biology of these trypanosomes,
mainly analyses of their isoenzymes and deoxyribonucleic acid, now appear to have
shown that T. "rhodesiense" cannot be distinguished from T. brucei brucei by any valid
and consistent criterion, while T. "gambiense" probably does constitute a valid subspecies
of T. brucei. There is still doubt whether populations of T. brucei are predominantly
clonal or sexual. While some form of genetic exchange undoubtedly can occur in this
species, its nature and frequency are unknown and there is evidence that the population
structure of T. brucei is essentially clonal.