Human Bipedalism, Evolved from Arboreal Locomotion of Two-arm Brachiation

TL;DR

This paper proposes that human bipedalism evolved from arboreal two-arm brachiation, a locomotion mode used by our ancestors, which influenced the development of upright posture and limb proportions.

Contribution

It introduces a hypothesis linking arboreal two-arm brachiation to the evolution of human bipedalism, emphasizing anatomical and locomotion adaptations.

Findings

Bipedalism may have originated from two-arm brachiation.

Evolution of foot structure with longitudinal arch supports upright walking.

Limb proportion changes made quadrupedal walking less feasible.

Abstract

Among all kinds of apes, only gibbons have the slim body as human. Gibbons can move in the forest by cross arm swing, what was the locomotion mode of our arboreal ancestor. Since our ancestor had much heavier body but weaker arms than gibbons, we suppose they had to move with two arm brachiation. Such mode of locomotion can account reasonably for the transition to bipedalism. Firstly, it needed our ancestor to straighten knee and hip joints and flex their lumbar spine. secondly, it evolved the feet of our ancestor with longitudinal arche. And most importantly, it made the ratio of the length of the upper limbs to that of the lower limbs unsuitable for quadruped walking.