The human level of intelligence is not necessary for survival, and in fact it may eventually result in our extinction.
Bacteria have no intelligence in the usual sense of the word, but they comprise about 90 percent of the cells you walk around with. They have far more survival advantages than the beasts with big brains.
And even within the human community there is no evidence that superintelligent people have more offspring than the average.
Then what was Cro-Magnon's advantage? less apt to get the flu?