New Study Suggests Tree Climbing Influenced Human Bipedalism Evolution

In a groundbreaking study published on July 29, 2025, researchers have suggested that the evolutionary journey of early humans towards bipedalism may have been significantly influenced by tree-climbing behaviors observed in modern chimpanzees living in dry, open savannah-like habitats. This research, conducted in the Issa Valley of Tanzania, highlights that despite the open terrain, chimpanzees frequently ascend trees to gather food, indicating that the adaptation of walking on two legs may not have solely evolved for terrestrial mobility but could also involve efficient navigation within arboreal environments.

The research, led by Dr. Rhianna Drummond-Clarke from the Max Planck Institute for Evolutionary Anthropology, challenges the long-held assumption that bipedalism arose purely from the necessity to traverse open ground. Dr. Drummond-Clarke stated, “For decades it was assumed that bipedalism arose because we came down from the trees and needed to walk across an open savannah. Here we show that safely and effectively navigating the canopy can remain very important for a large, semi-arboreal ape, even in open habitat.” This perspective marks a significant shift in understanding the evolutionary pressures that may have shaped early human ancestors.

The study observed the Issa Valley chimpanzees during the dry season, documenting their foraging behaviors and the types of trees they utilized. The researchers found that these chimpanzees rely heavily on trees for vital food sources, such as fruits, leaves, and flowers, despite the sparse distribution of trees typical of savannah-mosaic habitats. This reliance suggests that adaptations for climbing and foraging in trees were crucial for survival, potentially influencing the retention of arboreal traits among early hominins.

Dr. Drummond-Clarke and her team monitored the adults within the Issa community, recording the size, height, and structure of trees as well as the duration of foraging activities. Their findings revealed that chimpanzees spent considerable time foraging in larger trees that provided substantial food resources, indicating a strategic approach to foraging that balances the nutritional benefits of specific foods with the energy expenditure required to access them.

Moreover, the researchers noted that the chimpanzees employed unique strategies to navigate thinner branches safely, utilizing a combination of bipedalism and suspensory behaviors. This adaptability in tree-climbing may mirror the behaviors of early hominins, suggesting that bipedalism could have also evolved as a means to facilitate movement within tree canopies, not just on the ground.

However, Dr. Drummond-Clarke cautioned that further research is necessary to validate these conclusions. “This study only looked at foraging behavior during the dry season. Future studies on different communities of chimpanzees in similar habitats are essential to determine if these behaviors are consistent indicators of savannah-mosaic adaptations,” she stated. The implications of this research extend beyond understanding early human evolution, offering insights into the ecological dynamics of chimpanzee populations and their adaptive strategies to survive in changing environments.

This study contributes to a growing body of literature that seeks to reconstruct the evolutionary history of hominins, emphasizing the complex interplay between environmental factors and adaptive behaviors. As anthropologists and evolutionary biologists continue to investigate the roots of bipedalism, the findings from the Issa Valley serve as a compelling reminder of the intricate connections between climbing and walking in our primate relatives. The research underscores the need for a nuanced understanding of how adaptations may have evolved in response to both arboreal and terrestrial challenges faced by early human ancestors.