New research led by paleoanthropologists at the University of the Witwatersrand and the University of Southern California is shedding light on one of the most debated transitions in human evolution: when early hominins stopped regularly climbing trees and committed fully to walking on two legs. The findings suggest that early Homo had largely abandoned arboreal behavior by approximately 1.8 million years ago, marking a decisive shift toward a fully terrestrial lifestyle.
The study addresses a long-standing question in paleoanthropology about the timing and completeness of the transition from life in the trees to life on the ground. While it has long been accepted that bipedalism emerged early in the human lineage, researchers have debated how long climbing remained part of the daily repertoire of early hominins. Some species, such as Australopithecus, are thought to have combined walking on two legs with significant time spent in trees, using their upper limbs for both locomotion and climbing. The new analysis indicates that by the time early Homo appears in the fossil record, this dual strategy had given way to a more committed form of bipedalism.
The research, conducted by a team from two major institutions, examined fossil evidence to assess the degree of arboreal adaptation in early Homo. The results point to a clear reduction in features associated with regular tree-climbing, suggesting that these early humans were spending far less time in the canopy and more time navigating open landscapes on foot. This shift would have had profound implications for foraging, predator avoidance, and the ability to travel long distances across expanding savanna environments.
The transition away from tree-climbing is considered a key milestone in human evolution because it is tied to a suite of anatomical and behavioral changes. A fully terrestrial lifestyle would have freed the hands for tool use and carrying, while also reshaping the pelvis and lower limbs for more efficient upright walking. The timing proposed by the new study places this shift at roughly 1.8 million years ago, a period when early Homo was dispersing across Africa and beginning to show signs of increased brain size and technological innovation.
While the study does not claim that early Homo never climbed trees, it argues that regular arboreal behavior was no longer a central part of their survival strategy. Occasional climbing may have persisted, but the fossil evidence suggests it was no longer a routine activity. This distinction is important because it helps clarify the ecological niche of early Homo and how it differed from that of earlier hominins.
The research adds to a growing body of work that uses fossil anatomy to reconstruct behavior. By comparing skeletal features across species, paleoanthropologists can infer how ancient hominins moved and what habitats they preferred. The new findings support the view that early Homo was adapted to a more open, ground-based way of life, a shift that likely played a role in the species' ability to expand its range and eventually migrate out of Africa.
The study was led by researchers from the University of the Witwatersrand and the University of Southern California, continuing a long tradition of collaboration in the field of paleoanthropology. Their conclusions contribute to the ongoing effort to map the timeline of human evolution and to understand the environmental and behavioral pressures that shaped our earliest ancestors.
