I'm my mind, gene expression is at least as important as the coding genome.

AFAIU, the later mostly encodes the structure of proteins, which naively are the factory machines of or cells (enzymes, that is) and some of its building blocks. The gene expression tells the factory what to produce (a tail or an ear, say), when to produce it, and how much. More relevant to the topic of this article, the gene expression would determine which structures and pathways of the brains (or adrenal glands, or any other organs) to suppress, and which to reinforce and build up in a new generation of humans.

The building blocks are important, but once they are good enough, it matters more what you choose to build with them.