I think both thoughts could be correct. Without any real ability to deal with abstract concepts, sexual selection cannot function to enhance it.

First, there probably has to be a form of intelligence which would enhance survival, and a form of intelligence which could recognize the first as desirable.

After that, sexual selection might have favored the incremental enhancements by influencing development without very powerful genetic mutations, as you have said the genetic comparisons suggest.

Clearly, if one can breed for intelligence within Man, for instance, it will be developmental rather than genetic mutations which result in the changes. Doesn't lead to new species, though.

Interesting.