Sleeping sickness presents clinically as two distinct diseases, reflecting
the fact that two very different trypanosomes are responsible. The African
Rift separating East and West Africa defines the distribution of the two di
seases. In this review, Susan Welburn, Eric Fevre, Paul Coleman, Martin Odi
it and lan Maudlin discuss the biology and distribution of these two diseas
es in relation to the evolution of hominids in Africa.