Early human ancestors stopped swinging in trees and started walking on the ground sometime between 4.2 and 3.5 million years ago, according to a new study.This follows on the heels (sorry) of the recent studies on Ardipithecus, where it was found that this hominid had a skeletal pattern that was adapted not just for the trees but for bipedal walking as well. How long was this pattern maintained? Viegas continues:
This key moment, when our ancestors became anatomically and behaviorally less ape-like, coincides with increased cooling, more defined seasonality, and a grassland growth spurt. All transformed former forest habitats into more varied ones, forcing our very early relatives to change their ways.
"With the trees being farther apart, it became energetically advantageous for hominids to cross the gaps bipedally," said Gabriele Macho, lead author of the study that was published in the latest issue of Folia Primatologica.
The scientists observed that the Australopithecus anamensis wrist bones exhibited pressure loads associated with modern arboreal animals. The analyzed Australopithecus afarensis bones conversely showed stress loads comparable to those of more terrestrial species, including modern humans.A. anamensis is the form that followed, at least chronologically, Ardipithecus ramidus. Whether or not there is a direct ancestor/descendant relationship there, it is clear that the transitional elements in Ardipithecus were continued in the hominid line and that A. anamensis maintained a similar adaptation to the environment. The true changes in bipedalism and adaptation came with A. afarensis. This is yet another piece of the puzzle at this critical point in our history.
The researchers concluded that the important shift in early hominid lifestyle happened around the time when A. afarensis first emerged.
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