The good news is that molecular biology is rapidly advancing to the point where we can identify specific genes contributing towards certain traits eg:

Intelligence:

https://www.cambridgebrainsciences.com/more/articles/22-gene...

And aggression:

https://en.wikipedia.org/wiki/Monoamine_oxidase_A

As we continue to research, and hopefully one day allow embyro selection and gene insertion/deletion for genes linked these traits, we can resume the increase in IQ.

Epigenetics complicates things: https://en.wikipedia.org/wiki/Epigenetics but it just means we have more research to conduct!