In paleoanthropology, there has been an ongoing debate about the type of feet the last common ancestor (LCA) of humans and chimpanzees possessed. Some argue that they had feet similar to modern apes, ideal for vertical climbing, while others believe they had feet more like generalized monkeys, less suitable for vertical climbing. A recent study by paleoanthropologists from Dartmouth College and The Ohio State University focused on sooty mangabeys (Cercocebus Attis), known for their vertical climbing abilities. The research found that the LCA had the ability to flex its legs almost as much as a chimpanzee while climbing vertically, suggesting a tree-climbing lifestyle despite having a more ape-like anatomy.
Ardipithecus ramidus, a hominid that lived in Africa more than 4 million years ago. Illustration by Arturo Asensio, from Quo.es.
“Behavioral inferences from fossils are crucial in paleoanthropology. While some argue that monkeys lack the ability to climb vertically like great apes, our study points to functional equivalence. Even without chimpanzee-like legs, vertical climbing is possible,” said Dr. Luke Fannin from Ohio State University.
“Identifying the LCA is pivotal for understanding the evolution of bipedalism, a trait unique to humans,” he added.
The research highlights that despite having more ape-like foot morphology, early human ancestors could still climb trees like apes, shedding light on human evolution through understanding movement patterns.
The study by Fannin and his team focused on observing a sooty mangabey in Ivory Coast’s Tay National Park, using video recordings to analyze ankle and midfoot flexion during climbing.
While African apes rely on ankle hyperextension for climbing, mangabeys exhibit flexibility in the midfoot region, known as the midfoot break. This adaptation allows mangabeys to climb vertically by bending their midlegs, compensating for limited ankle mobility.
This finding challenges the notion that an ape-like midfoot anatomy would hinder early human ancestors in vertical climbing activities, suggesting that both ape-like and monkey-like feet could support tree-climbing behaviors.
Cercocebus Attis). Image credit: Luke Fannin, Dartmouth College.” width=”580″ height=”435″ srcset=”https://cdn.sci.news/images/2023/09/image_12249-Cercocebus-atys.jpg 580w, https://cdn.sci.news/images/2023/09/image_12249-Cercocebus-atys-300×225.jpg 300w” sizes=”(max-width: 580px) 100vw, 580px”/>
Sooty Mangabey (Cercocebus Attis). Image credit: Luke Fannin, Dartmouth College.
This study challenges the traditional view of the “monkey’s foot LCA” debate, suggesting that different foot structures can still support efficient tree climbing. The results imply that early human ancestors with various foot morphologies could have engaged in safe and frequent tree climbing activities.
“By demonstrating that vertical climbing can be achieved with different foot anatomies, this study adds complexity to our understanding of primate evolution and movement patterns,” said W. Scott McGraw, a professor at Ohio State University.
The findings, published in the Proceedings of the National Academy of Sciences, provide insights into the kinematic convergence of apes and monkeys during vertical climbing, shedding light on early arboreal life in humans.
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Luke D. Fannin et al. 2026. Kinematic convergence in vertical climbing of apes and monkeys informs debates about early arboreal life in humans. PNAS 123 (35): e2608183123; doi: 10.1073/pnas.2608183123
Source: www.sci.news
