Human ancestors first walked in trees

Human ancestors first walked in trees not savannas

Human ancestors first walked in trees
mongabay.com
May 31, 2007

Walking on two legs is likely to have first arisen among apes living in trees, rather than ground-dwelling prehistoric ancestors of humans, reports research published in the June 1st issue of the journal Science.

Orangutan in Sumatra. Photos by Jen Caldwell.

Upright walking has long been thought to be a defining characteristic of hominids. One of the leading theories, known as the savannah hypothesis, held that “the ancestors to chimps, gorillas and humans descended from the trees and began walking on the ground on all fours,” stated a release from AAAS, the nonprofit society that publishes Science. “Over time, this four-legged gait would have evolved into the ‘knuckle-walking’ that chimps and gorillas still use today and then into upright, two-legged walking in humans.”



However new research complicates this explanation. Observing wild orangutans in Sumatra, Indonesia, a team of researchers led by Susannah Thorpe of the University of Birmingham in Birmingham found evidence of “hand-assisted bipedalism” as they move about the trees of the rainforest canopy.

“Our conclusion is that arboreal bipedalism had very strong adaptive benefits. So, we don’t need to explain how our ancestors could have gone from being quadrupedal to being bipedal,” said Susannah Thorpe, lead author of the paper.

To explain the evolution of bipedalism in our ancestors, Thorpe and colleagues propose a scenario that begins as other researchers have envisioned. AAAS explains:

“Somewhere toward the end of the Miocene epoch (24 to 5 million years ago), climate in East and Central Africa became alternately wetter and drier, and the rainforest grew increasingly patchy. Apes living in the forest canopy would have begun to encounter gaps between trees that they could not cross at the canopy level.”



“The Science authors suggest that early human ancestors responded to this by abandoning the high canopy for the forest floor, where they remained bipedal and began eating food from the ground or smaller trees. The ancestors of chimps and gorillas, on the other hand, became more specialized for vertical climbing between the high canopy and the ground and thus developed knuckle-walking for crossing from one tree to another on the ground.”




Thorpe et al (2007) “Origin of Human Bipedalism as an Adaptation for Locomotion on Flexible Branches”. Science 1 June 2007.