It is an interesting proposition. Recursive thought basically allows humans to do things like count and have our “inner voice”. This type of thought is not present in animals. So when did it emerge in humans? The author posits 50 to 100 thousand years ago for women and much more recently for men. Perhaps the holocene or even more recently.
This type of thought is BELIEVED TO BE not present in animals.
“This type of thought is not present in animals.”
Rather, we don’t believe this type of thought is present in animals. It is impossible for us to actually know what is present in the thoughts of animals, because we can’t experience that, observe it, or measure it in any reliable way. The best we can do is try to come up with tests that might detect it if it was present, by the external reactions and behavior of the animals.
“So when did it emerge in humans?”
The question is based on an unsupported assumption. We have no idea that it ever “emerged” at all. For all we know the first human to exist already had the capability.