A new study found that chimps walk more upright than previously thought, signifying a resemblance with humans.
Humans exhibit coordinated rotation of the thorax and pelvis while walking, which is made possible by adaptations for trunk flexibility. Chimpanzees are humans' closest relatives in nature but it has long been believed that the two species do not share the same flexibility of the torso while walking.
To investigate, researchers from the Stony Brook University embarked on a study to see if chimpanzees exude bodily rotations during bipedal walking, just like humans.
The study involved five male and five female human subjects, as well as two male chimpanzees (Pan troglodytes). All the subjects were instructed to walk on a runway that is 11 meters (36 feet) long. The humans were given sufficient time to practice prior to the actual test. During the test time, they were asked to walk in a pace that is comfortable for them.
The chimpanzees have been trained to walk bipedally for about two years and have been found to show proficient behavior before the execution of the experiment. During the test, the chimpanzees were either asked to follow a trainer with a juice at hand as a reward or instructed to walk depending on their preference.
The researchers utilized three-dimensional (3D) kinematics to see if chimps truly have rigid trunks during bipedal walking. They divided the torso into three sections: the thorax, lumbar area and pelvis. Overall range of motion (ROM) for each segment were measured.
The findings of the study, published in the journal Nature Communications, showed that the overall ROM in the transverse plane relative the holistic coordinate system (absolute ROM) of chimpanzees were notably higher than in humans for all the segments.
The lumbar area rotates in a synchronous manner with the pelvis, in both humans and chimps.
The thorax of humans moved in opposite direction of the pelvis. The thorax of the chimpanzees, on the other hand, was found to rotate in the same direction as the pelvis; however, the thorax rotated much lesser compared to the pelvis.
"During walking, we actually observed as much rotation within the torsos of chimpanzees as in humans," said Nathan Thompson, lead author and a PhD student at Stony Brook University. This refutes the ancient belief that the skeleton of the chimps are the sole basis for its movement.
The study also suggests that early human ancestors may have walked just like present-day humans and chimpanzees, such that upper body rotations were opposite of pelvic rotation. Thompson said that as more information about how chimps move become available, experts are able to learn more about the isolated groups of early human bones. "Only then can we paint a complete picture of how we evolved into what we are today," he closed.
Photo: Eric Kilby | Flickr
