Uplift of the roof of africa and its bearing on the evolution of mankind

Abstract

Evidence concerning the geomorphological evolution of the Western Rift Valley, sedimentation within the valley and comparison of the fossil mammalian faunas of Western Uganda and East Africa indicate that the mountain ranges which now flank the Western Rift were uplifted in three or more stages beginning during the upper Miocene and that they reached climatically important altitudes during the upper Pliocene, at which time they began to modify regional climatic patterns in East Africa. Their main effect was the xerification of conditions over much of the region east of the mountains. The regional climatic effects due to the mountain ranges were themselves modified by global climatic changes related to the onset of the Glacial Period, the two phenomena combining to yield the Present day climatic regime of East Africa. As the climate changed, so did the flora and fauna. Faunal response was of three main kinds: a) dispersal into East Africa of pre-existing forms already adapted to more xeric conditions (many bovids, some cercopithecids), b) autochthonous evolution of forms adapted to mesic environments into forms adapted to more xeric conditions (suids, elephantids, some bovids, hominids), c) displacement of species ranges of those lineages unable to adapt to changing conditions (i.e. local extinctions) (Anancus, Brachypotherium). Autochthonous evolvers, including hominids, adopted two main strategies reflected in their hard anatomy: a) dietary shift (suids, proboscideans, bovids and later Pliocene hominids) and b) locomotor changes (early Pliocene hominids).