Brachiation:
Brachiation (from “brachium”, Latin for “arm”), or arm swinging, is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms. During brachiation, the body is alternately supported under each forelimb. [Wikipedia]
Noted in “The brain’s secret powerhouse that makes us who we are,” Caroline Williams, NewScientist (7 July 2018, paywall):
[Neuroscientist Robert] Barton suspects that what started this unlikely growth spurt was the challenge of moving a much larger body through the trees. While small primates can run along the branches, even gibbon-sized apes are too heavy to do the same, at least without holding on to branches above. This led apes to make a switch to swinging through the branches, known as brachiation, which in turn made the ability to plan ahead a distinct advantage. “Brachiation is a relatively complex locomotor strategy,” says Barton. “It involves fine sensory motor control, but it also involves a need to plan your route so that you can avoid accidents.”
