untermensche
Contributor
As with other great ape language experiments, the extent to which Koko has mastered and demonstrates these signs was disputed in a study published in 1999.[4] But it is generally accepted that she does not use syntax or grammar, and that her use of language does not exceed that of a young human child.
https://en.wikipedia.org/wiki/Koko_(gorilla)
A lot of the so-called evidence in the case of the gorilla named Koko is merely the claims of the person who taught her.
What the case shows is that in spite of the great effort, a gorilla could not be taught to comprehend human language.
It's innate abilities of animal communication, not human language, could be extended with great effort however.
And in terms of young children there is evidence they understand a lot more than they can express. It is doubtful this gorilla had even a very young child's ability to comprehend language.
And Neanderthal had intelligence. What it lacked was the ability to innovate that you would expect to see in an animal with language.