Knuckle-walking is a form of quadrupedal locomotion in which the weight of the body is borne on the knuckles of the hands rather than on the palms. Knuckle-walking is an efficient way to move on all fours because it allows for a long stride and a high degree of mobility. Some primates, such as chimpanzees and gorillas, are knuckle-walkers.

However, humans are not knuckle-walkers. There are several reasons for this, including:

* Humans have shorter arms than chimpanzees and gorillas. This means that humans would have to stoop down more to knuckle-walk, which would put them at a disadvantage when it comes to running and climbing.

* Humans have larger brains than chimpanzees and gorillas. This means that humans have a higher center of gravity, which makes them less stable when they are on all fours.

* Humans have more versatile hands than chimpanzees and gorillas. This means that humans can use their hands for a wider variety of tasks, such as grasping objects and manipulating tools.

As a result of these factors, humans evolved to walk upright on two legs. This allowed us to free up our hands for other tasks, which ultimately led to the development of human civilization.