Data from chacma baboons (Papio cynocephalus ursinus) are used to asse
ss the impact of environmental variables on male and female body weigh
t. The most influential factors were found to be mean annual rainfall
and temperature. The nature of the relationship differed from that pre
viously described for the genus Papio as a whole. This was due to the
inclusion of the ecologically distinctive Drakensberg Mountain populat
ion. We consider the implications of the finding.