Popper unintentionally took a stance on one of the requirements for being a universal explainer (or General Intelligence). Specifically, he argued that language was a requirement for his epistemology to work and thus a requirement for general intelligence:
The most important of human creations, with the most important feed-back effects upon ourselves and especially upon our brains, are the higher functions of human language; more especially the descriptive function and the argumentative function.
Human languages share with animal languages the two lower functions of language: (1) self-expression and (2) signallying. …All animal languages and all linguistic phenomena share these two lower functions. …The two most important higher functions of human languages are (3) the descriptive function and (4) the argumentative function.
With the descriptive function of human language, the regulative idea of truth emerges, that is, of a description which fits the facts. Further regulative or evaluative ideas are content, truth content, and verisimilitude.
The argumentative function of human langue presupposes the descriptive function: arguments are, fundamentally, about descriptions: they criticize descriptions from the point of view of the regulative ideas of truth; content; and verisimilitude.
Now two points are all-important here:
(1) WIthout the development of an exosomatic descriptive language – a language which, like a tool, develops outside the body – there can be no object for our critical discussion. But with the development of a descriptive language (and further, of a written language), a linguistic third world can emerge; and it is only in this way, and only in this third world, that the problems and standards of rational criticism can develop.
(2) It is to this development of the higher functions of language that we owe our humanity, our reason. For our powers of reasoning are nothing but powers of critical argument.
With the evolution of the argumentative function of language, criticism becomes the main instrument of further growth.Objective Knowledge, p. 120-121
Deutsch has argued that we may not be born universal explainers and that we may acquire part of the necessary program via memes. (BoI, p. 415) If Popper is correct in his argument, then “descriptive and argumentative language functions” is at least one meme (or rather a memeplex) we must acquire before we can be true universal explainers. This might explain why people without language consistently are not universal explainers and have limited intelligence until they acquire language.
However, there is a bit of an explanatory gap here worth mentioning. What exactly is the difference between being a universal explainer (with the needed language functions) and being a potential universal explainer (without language but you could, unlike an animal, acquire it if given the chance.)