For decades, the prevailing image of early human evolution has been clear: as ancient forests gave way to Africa’s open savannah, our ancestors were forced to leave the trees and adapt to life on the ground. Walking upright, according to this long-held view, was simply a matter of survival.
But a groundbreaking study led by researchers at the Max Planck Institute of Evolutionary Anthropology in Germany challenges that assumption. Instead of learning to walk on the savannah, early humans may have taken their first upright steps in the trees.
Clues from Issa Valley chimpanzees
To explore this question, scientists studied the behavior of chimpanzees in Tanzania’s Issa Valley. These apes live in savannah-mosaics — dry, open woodlands that resemble the landscapes early hominins once inhabited. Despite the harsh environment, Issa Valley chimpanzees spend just as much time in the trees as their forest-dwelling cousins.
Food plays a big role. Many of their meals require extra effort, such as extracting seeds from pods or chewing fibrous unripe fruit. Because of their size, chimpanzees often navigate these trees by suspending themselves from branches or by standing and walking upright while using nearby branches for support.
This arboreal bipedalism, the researchers argue, may mirror how early humans first experimented with walking on two legs.
Rethinking the Miocene landscape
Toward the end of the Miocene Epoch (23–5.3 million years ago), Africa’s forests began transforming into more open savannahs. Traditionally, this ecological shift has been seen as the trigger for habitual bipedalism.
Yet fossil evidence tells a more complex story. Several late Miocene hominins still showed strong tree-dwelling traits, such as elongated arms and curved fingers. Dental wear and isotope studies also suggest that even after moving into open habitats, early humans relied heavily on tree-based foods.
“We suggest our bipedal gait continued to evolve in the trees even after the shift to an open habitat,” explains study author Rhianna Drummond-Clarke.
Walking upright: practice in the trees
According to the study, the trees may have served as “training wheels” for our ancestors. Upright walking could be practiced in relative safety, with branches available for balance. Over time, this skill may have translated to the ground, allowing early humans to navigate longer distances across open terrain, search for scattered food sources, and eventually spread across the globe.
The findings not only reshape our understanding of human evolution but also highlight the value of studying modern chimpanzees. Their behaviors may still echo the strategies of our earliest ancestors — and shed light on how one of humanity’s most defining traits, bipedalism, first took root.
