Scientists have long focused on how climate and vegetation allowed human ancestors to evolve in Africa. Now, University of Utah geologists are calling renewed attention to the idea that ground movements formed mountains and valleys, creating environments that favored the emergence of humanity.
“Tectonics [movement of Earth’s crust] was ultimately responsible for the evolution of humankind,” Royhan and Nahid Gani of the university’s Energy and Geoscience Institute write in the January, 2008 issue of Geotimes, published by the American Geological Institute. They argue that the accelerated uplift of mountains and highlands stretching from Ethiopia to South Africa blocked much ocean moisture, converting lush tropical forests into an arid patchwork of woodlands and savannah grasslands that gradually favored human ancestors who came down from the trees and started walking on two feet – an energy-efficient way to search larger areas for food in an arid environment.
In their Geotimes article, the Ganis – a husband-and-wife research team who met in college in their native Bangladesh – describe this 3,700-mile-long stretch of highlands and mountains as “the Wall of Africa.” It parallels the famed East African Rift valley, where many fossils of human ancestors were found.“Because of the crustal movement or tectonism in East Africa, the landscape drastically changed over the last 7 million years,” says Royhan Gani, a research assistant professor of civil and environmental engineering. “That landscape controlled climate on a local to regional scale. That climate change spurred human ancestors to evolve from apes.”
Hominins – the scientific word for humans (Homo) and their ancestors (including Ardipithecus, Paranthropus and Australopithecus) – split from apes on the evolutionary tree roughly 7 million to 4 million years ago. Royhan Gani says the earliest undisputed hominin was Ardipithecus ramidus 4.4 million years ago. The earliest Homo arose 2.5 million years ago, and our species, Homo sapiens, almost 200,000 years ago.Tectonics – movements of Earth’s crust, including its ever-shifting tectonic plates and the creation of mountains, valleys and ocean basins – has been discussed since at least 1983 as an influence on human evolution. But Royhan Gani says much previous discussion of how climate affected human evolution involves global climate changes, such as those caused by cyclic changes in Earth’s orbit around the sun, and not local and regional climate changes caused by East Africa’s rising landscape.
“Although the Wall of Africa started to form around 30 million years ago, recent studies show most of the uplift occurred between 7 million and 2 million years ago, just about when hominins split off from African apes, developed bipedalism and evolved bigger brains,” the Ganis write.
“Nature built this wall, and then humans could evolve, walk tall and think big,” says Royhan Gani. “Is there any characteristic feature of the wall that drove human evolution?”
The answer, he believes, is the variable landscape and vegetation resulting from uplift of the Wall of Africa, which created “a topographic barrier to moisture, mostly from the Indian Ocean” and dried the climate.