Molecular dating puts the human/chimpanzee split somewhere between four and six million years (eg. Takahata and Satta 1997; Caccone and Powell 1989).    At this time, much of Northeast Africa was experiencing a sea level rise at the end of the warm Miocene (23 - 5.3 Ma) and very beginning of the Pliocene (5.3 - 1.8 Ma). Although during the Pliocene a global cooling effect is seen, there were many rises and falls of sea levels as glaciations began to take place in the Northern Hemisphere. The entire Pliocene can be considered a time of great fluctuations in sea levels and climate.

It is possible that these waters provided the environmental niche required to initiate wading behaviours, and with time swimming and diving, in those primates who remained in these wet environments.