Human ancestors may have started bipedal foraging among the treetops in the open, researchers have suggested, challenging the idea that the behavior evolved to adapt to spending a lot of time on the ground.
The origin of bipedalism in hominins around 7m years ago has been thought to be related to environmental change, when dense forests began to give way to open woodlands and grasslands. In such cases, it has been argued, our ancestors would have spent more time on the ground than in trees, and would have been able to walk more efficiently on two legs.
But now researchers studying chimpanzees in Tanzania say the trait may have had a different origin. “I think we’ve been telling this plausible story for a long time, which at least our data doesn’t really support,” said Dr Alex Piel, a biologist at the University of London and co-author of the study.
Writing in the journal Science Advances, the researchers report how they spent 15 months studying 13 chimpanzees living in the Issa Valley in western Tanzania, an environment similar to that of our ancestors. the hall they had.
The results reveal that these chimpanzees spend more time on the ground, moving, in open areas of forest and grass than in densely forested areas in the same area.
However, even in the open environment, the proportion of time the chimpanzees spent on the ground was similar to that previously reported for other chimpanzee populations living in densely forested areas, including Gombe and Mahale.
“Although we have very few trees, [the chimps are] it no longer belongs to the world,” said Piel.
The team combined data from different sites in Issa Valley and analyzed how often the chimpanzees stood or walked on two legs.
The results reveal that although bipedal behavior was less than 1% of the recorded situations, only 14% related to chimpanzees on the ground.
“Most of the time they are bipedal in trees,” said Piel, adding that the behavior, at least in the branches, seems to be closely related to foraging.
Rhianna Drummond-Clarke, the first author of the study from the University of Kent, said that open space would have favored the two chimpanzees, as well as the ancestors of early humans, because such an environment has a lot of trees. more dense forests.
“[Bipedalism may help them] Move safely and efficiently in flexible branches and get as many results as possible when they get them,” he said.
The team says that while the study can’t prove that our ancestors showed the same behavior twice, it calls into question the conventional wisdom about how humans ended up walking on their feet. two grasses, and they suggest that trees continued to play a role in our evolutionary story. even as the environment changes.
“Instead of having time on the ground which is exciting [bipedalism], may have caused it, but it was already there,” said Piel. And that fits well with the fossil record because all of these early hominins have an adaptation to shrubs and earth.