Only quickly skimmed the beginning of this very long essay, but aren't Algernon's story and the first paragraphs of the essay about the impossibility of increas

Only quickly skimmed the beginning of this very long essay, but aren't Algernon's story and the first paragraphs of the essay about the impossibility of increasing the intelligence of a single individual? And what does evolution have to do with it? It seems to be impossible to increase the intelligence of, say, an average individual; yet Einsteins exist, there is actually a large number of them in absolute terms. One thing is the average level of human intelligence, evolutionarily determined; a completely different thing is the possibility of increasing the IQ of specific individuals during their lifetimes.