Having just read it, I think it without a doubt that this next passage of Tolkien’s is echoing G.K. Chesterton’s first chapter of The Everlasting Man, where he derides the modern idea of the “cave man” and all the silly conjecture surrounding him.
It’s no surprise that Tolkien was annoyed when critics appealed to the cave man image as a reason for why fiction like his should not be taken seriously.
“Their taste remains like the taste of their naked ancestors thousands of years ago; and they seem to like fairy-tales better than history, poetry, geography, or arithmetic.” But do we really know much about these “naked ancestors,” except that they were certainly not naked? Our fairy-stories, however old certain elements in them may be, are certainly not the same as theirs. Yet if it is assumed that we have fairy-stories because they did, then probably we have history, geography, poetry, and arithmetic because they liked these things too, as far as they could get them, and in so far as they had yet separated the many branches of their general interest in everything.
-J.R.R. Tolkien, On Fairy-Stories, (Children)