What characterizes knuckle-walking in primates?

Knuckle-walking in primates is characterized by the adaptation of strong arms that support upper body weight. This unique form of locomotion is primarily observed in certain species of African apes, such as chimpanzees and gorillas. When these primates walk on all fours, they do so by placing their knuckles on the ground, which allows their forelimbs, which are relatively strong and muscular, to bear their body weight effectively.

The effect of this adaptation is that it provides balance and support while maintaining a degree of stability during movement. The strong upper body and forelimbs are essential for knuckle-walking because they help to counterbalance the weight of the body and facilitate a stable gait over various terrains. This adaptation is not just functional for locomotion; it also allows these primates to engage in behaviors such as climbing and swinging in trees, which are integral parts of their survival.

The other aspects mentioned—such as the use of only the hind limbs, the proportions of forelimbs to hind limbs, and the flexibility of the lumbar region—do not accurately characterize knuckle-walking, as this locomotion relies heavily on the use and strength of the forelimbs rather than limiting movement to the hind limbs or focusing solely