About 3.2 million years ago, the early homin Australopithecus afarensis had arches in the soles of its feet --- a key adaptation for walking on the ground -- but its long arms and slender fingers convinced some researchers it was still comfortable with climbing, which would be expected if australopithecines slept in trees at night to escape predators as most chimps do today, the researchers said.
It had been thought hominins may not have slept on the ground until Homo erectus appeared 1.9 million years ago, possible using fires to ward off predators as they slept.
However, researchers from Cambridge University studying West African chimpanzees in Guinea found widespread use of sleeping nests on the ground rather than in trees, NewScientist.com reported Thursday.
While the chimps in Guinea have few predators, similar ground nests are seen in the Democratic Republic of the Congo where leopards are also present, researchers said.
"Ground nesting can become established despite the presence of predators and without the use of fire," Cambridge researcher Kathelijine Koops said, suggesting australopithecines may have slept on the ground too.
Some other researchers agree, pointing out the anatomy of A. afarensis shows its ability to climb trees was compromised.
"It's nice to have a study that indicates that [ground-sleeping] is not necessarily related to the adoption of fire," Tim White at the University of California-Berkeley said.