But oh, I tell you he could run on all-fours! Now this was something at which we were particularly awkward.

Furthermore, it was a rare individual among us who balanced himself with his knuckles when walking.

Such an individual was an atavism, and Red-Eye was an even greater atavism.
That is what he was--an atavism.

We were in the process of changing our tree-life to life on the ground.

For many generations we had been going through this change, and our bodies and carriage had likewise changed.
But Red-Eye had reverted to the more primitive tree-dwelling type.
Perforce, because he was born in our horde he stayed with us; but in actuality he was an atavism and his place was elsewhere.
Very circumspect and very alert, he moved here and there about the open space, peering through the vistas among the trees and trying to catch a glimpse of the hunting animal that all suspected had pursued me.
And while he did this, taking no notice of me, the Folk crowded at the cave-mouths and watched.
At last he evidently decided that there was no danger lurking about.