Chimpanzees are highly adaptable primates that exhibit a diverse range of movements across various environments. Their locomotion allows them to navigate both arboreal (tree-dwelling) and terrestrial (ground-dwelling) habitats effectively. These movements showcase their physical versatility. Chimpanzees can move quadrupedally, on all fours, and also bipedally, on two legs, demonstrating a flexible approach to getting around.
Knuckle-Walking
Knuckle-walking is the predominant form of terrestrial locomotion for chimpanzees, where they support their upper body weight on the knuckles of their forelimbs. This involves a partially flexed posture of their fingers, allowing the body’s weight to be transferred through these joints to the ground. The anatomy of their wrists is specialized for this movement, allowing for an extended wrist posture during the stance phase. This differs from gorillas, which use a more columnar or straight wrist posture.
This method of movement offers several benefits, including protecting the fingers and providing stability when moving across varied terrain. Their hands, with long fingers and short thumbs, are adapted for grasping branches, which also influences their knuckle-walking.
Occasional Bipedalism
While knuckle-walking is their primary mode of ground locomotion, chimpanzees are capable of walking on two legs, a gait known as bipedalism. This form of movement is typically adopted in specific situations rather than for sustained travel. For instance, they may walk bipedally when carrying food or tools, as it frees their hands. Bipedalism is also observed during displays, such as when a male chimpanzee stands upright to appear larger and assert dominance.
Chimpanzee bipedalism is characterized by a “bent-hip, bent-knee” posture, meaning their hips and knees remain significantly flexed throughout the walking cycle. Their trunk also tends to lean forward. This differs from human bipedalism, which involves a more extended posture of the limbs. They generally do so for short periods, and this movement appears to have similar energy costs to their quadrupedal locomotion.
Chimpanzee Walking Versus Human Walking
The walking styles of chimpanzees and humans differ significantly due to distinct anatomical adaptations. Humans are obligate bipeds, meaning two-legged walking is their primary and most efficient mode of locomotion, characterized by a striding gait with an upright posture and extended limbs. In contrast, chimpanzees primarily knuckle-walk, and their bipedalism is facultative and less efficient for long distances.
Key anatomical differences contribute to these distinct gaits. The human pelvis has curved iliac blades, which allow the gluteal muscles to stabilize the body during single-leg support, preventing sideways collapse. Chimpanzees, however, have flat iliac blades, leading to different muscle orientation and a more pronounced sway or wider arc of pelvic rotation during bipedal walking to maintain balance. Furthermore, the human foot is structured to efficiently store elastic energy for propulsion, with a more anterior center of pressure for stability, unlike the chimpanzee foot, which is adapted for grasping with an opposable big toe. These fundamental differences in skeletal and muscular structure underpin the unique biomechanics and energetic costs of walking for each species.