Koko appeared much, much more in the media and pop sci publications than the actual scientific literature. There are also a number of researchers who questioned

Koko appeared much, much more in the media and pop sci publications than the actual scientific literature. There are also a number of researchers who questioned Koko in the literature, including people that tried to replicate with their own animals. There is really no way to make an argument from authority here, because Koko is a controversial topic among the "authorities". The OP is right that Koko stumbled around a lot, even after the signs had supposedly been "mastered". This article presents one of the more bizarre results of that: https://slate.com/technology/2018/06/koko-the-ape-obituaries-are-overlooking-her-nipple-fetish-and-other-important-things.html https://slate.com/technology/2018/06/koko-the-ape-obituaries... We probably are underrating animal intelligence, and whether Koko understood language is largely dependent on what one considers to qualify as "language" - there definitely were some impressive displays of intelligence at times. But through an unbiased lens I think it's also pretty clear the researchers were constantly making the most charitable possible interpretation of Koko's signs. As far as the GP comment, it is well documented that zero as a mathematical concept was developed surprisingly late, while the concept of "nothing" existed prior to any formal notion of integers at all. The Quanta article is conflating "nothing" with "zero", although perhaps the original research makes the distinction more clear.