I once heard a naturalist and nature photographer who specializes in wildlife and plants explain his interest in geology by saying, “You have to have something to put those ecosystems on!” His point was that different geological features give rise to different climates, soil conditions, and other factors that shape the living things that inhabit them, and to understand the inhabitants you have to understand the place. Two geologists at the University of Utah take this idea a bit further; they suspect that geological change played a major role in the evolution of early hominins in east Africa several million years ago.
Climate change drove our ancestors out of the trees; the forest dried up and changed to savannah, and they had to adapt to the different conditions. Some of the adaptations were probably instrumental in shaping the hominins into modern humans. But what caused the climate change?
Royhan and Nahid Gani have examined a stretch of the Wall of Africa, a chain of mountains and highlands that runs from Sudan to South Africa, and determined that the land rose by at least a kilometer (about 3,200 feet) three to six million years ago. The uplift in the area they looked at (in Ethiopia) cut the land off from much of the moisture coming from the Indian Ocean, and in doing so changed the climate and the living conditions for the primates in the area, who had to scramble to cope. Instead of living in lush jungle-like conditions, they found themselves in a much less densely vegetated and drier area. Bipedalism may be one of the most crucial adaptations to the changed landscape.
The uplift is part of the tectonic history of the region, which involves the movement of two of the plates that make up the crust of the earth. The plates are pulling apart, creating a huge rift system several thousand miles long that runs from Lebanon in the north down through the African Rift Valley and on to Mozambique. A large plume of molten rock swells toward the surface under the rift system, pushing the rocks above to either side. From such subterranean forces, much follows, including perhaps you and me.
The Ganis speculate that in addition to driving the shift to bipedalism by pushing up the Wall of Africa, the tectonic activity in the area may have driven further hominin evolution by providing varied and changeable landscapes that required ingenuity on the part of their primate inhabitants. Further research may help determine more precisely the influence that the geology of its birthplace had on humankind.
If you want a quick read that will tell you more about this work, here’s a story from Live Science. For more detail, I highly recommend this press release from the University of Utah (check out the links on the left for some nice images).
