Mark Cane, together with Peter Molnar, have concluded that the
closing of the Indonesia Seaway in the last 3-5 million years has
effected the aridification of East Africa (when and where humans
evolved), and may have provided the switch that initiated the cooling
leading to the ice ages.
Closing of the Indonesian seaway precursor to African aridificaton
3-4 million years ago.
Cane, M. A., Molnar, P., 2001: Closing
of the Indonesian seaway as a precursor to east African aridification
around 3-4 million years ago. Nature, 411, 157-162.