If you look at the history of human evolution, this doesn't make sense. Evolution was very very slowly increasing human intelligence by, e.g., making our skulls bigger. Then we got to the point where we could use language/transmit knowledge between generations/etc. and got up to technological, spacefaring civilization in, evolutionarily speaking, no time whatsoever. This is not a story which suggests that human intelligence is some sort of maximum, or that evolution was running into diminishing returns and so stopped at human intelligence. It suggests that human intelligence is the minimum intelligence necessary to produce the kind of generational transfer that gets you up to technological civilization.