Gibbons seem to be all the rage, lately. A new biophysics paper on the gait of Gibbon bipedalism has been the most recent news that I have caught in my search of current events in primatology. The paper, “The dynamics of hylobatid bipedalism: evidence for an energy-saving mechanism?” was published four days ago in the Journal of Experimental Biology. It overviews how Gibbons moved on the ground based on the concern that there is some common energy-efficiency pattern in all primates that are fundamentally adapted to arboreal environments, but that can also stand up and walk. It turns out, they do just fine on two legs, but their gait is much different from ours.
Specifically, Evie E. Vereecke and two colleagues introduced an ‘instrumented walkway’ to the enclosure of four white-handed gibbons (Hylobates lar) in a Belgian zoo. As the apes ambled over it, their every move was filmed and every footfall recorded. The methodology reminds me of Eadweard Muybridge‘s studies on human gait.
Gibbons are anatomically much different than any other ape. They have outrageously large arms compared to their legs and rest of their bodies. This is because gibbon arm length is proportional to how the ape moves throughout its environment. The animals are much more often found swinging from limb to limb than “walking” on the ground.
Humans have two very distinct gaits, walking and running, gibbons only rarely engage in a way of locomotion that resembles our walk, where the legs are swung like pendulums. Instead, at all speeds, they propel themselves in a springy, bouncy fashion closer to our run. Here’s a video that I uploaded of a gibbon on the run.
And, unlike humans, Vereecke reports that gibbons do not use their Achilles tendons as the main spring. Vereecke hypothesizes that they might use their quadriceps muscles instead. Also unlike a human, they never have both feet off the ground at the same time. Vereecke suggests that this ‘aerial phase’ (think of this lovely expression on your next jog) should not be a requirement to call something a run.
The study concludes that gibbons make use of a energetically efficient spring-mass mechanism during bipedal locomotion.