Chimpanzees and gorillas are quadrupedal, walking on four legs. Their hands land on their knuckles, not their palms. Orangutans sometimes walk on their knuckles also.

Elaine and most primatologists think that knuckle-walking is a primitive trait — that the last common ancestor of gorillas, chimps, and humans was a knuckle-walker, and then the human branch evolved to became bipedal. 

Marc Verhaegen has a different version: the last common ancestor of gorillas, chimps, and humans was bipedal. The gorilla-branch and chimp-branch then evolved independently to be knuckle-walking quadrupeds, while the human-branch remained bipedal. 

Elaine Morgan wanted to discuss the pros and cons of that topic, without arguing too much with Marc about it. So she initiated the thread 'Knuckle-walking' in the AAT discussion group on May 6, 2012, and discussed it mostly with her fictional characters Rob Dudman and m3dodds (Bill) for the next month. These were the last messages in which Elaine posted messages under her own name. After that, she only posted messages as Rob Dudman and m3dodds (Bill).

This thread Knuckle-walking is copied from this address:

https://groups.io/g/AAT/topic/64992109#58936