It has long been believed that our prehistoric ancestors started walking on two legs as they moved from the trees into the more open environment of the African savanna. A new study of chimpanzees, however, suggests that such may not have been the case.
Known as the Savanna Hypothesis, the prevailing theory suggests that as tropical forests began receding due to natural climate change, the early hominins that lived in the trees of those forests started venturing out into the savanna. Because the savanna consisted of a mix of woodlands and grasslands, the apes gradually began walking upright, in order to better traverse the open spaces.
All of that having been said, not everyone completely buys into the hypothesis. Among those who now question it are scientists from University College London, the University of Kent, and Duke University in North Carolina, who conducted the recent study.
Over a 15-month period, the researchers observed a group of 13 wild adult chimpanzees living in the Issa Valley of western Tanzania. The "savanna-mosaic" landscape of that region is very similar to that of our early ancestors, consisting of a mix of dry open land and patches of forest. Because chimps are humankind's closest living relatives, it seems likely that over the millennia, the Issa population would adapt to their landscape in a manner similar to that of prehistoric hominins.
Refuting the Savanna Hypothesis, it was found that the Issa chimpanzees spent just as much time in the trees as their counterparts living in dense forest environments, rarely going out into the grasslands. Additionally, even when they did make their way across the open ground, they still tended not to walk upright. In fact, over 85% of the occurrences of bipedalism that were observed took place when the apes were in the trees.
"Our study suggests that the retreat of forests in the late Miocene-Pliocene era around five million years ago and the more open savanna habitats were in fact not a catalyst for the evolution of bipedalism," said University College London's Dr. Alex Piel, co-author of a paper on the study. "Instead, trees probably remained essential to its evolution – with the search for food-producing trees likely a driver of this trait."
The paper was published this week in the journal Science Advances.
Source: University College London via EurekAlert
