We traded natural selection for cultural selection

Which is natural. Nothing was traded.

We transitioned from* 😉
I'd love to hear some musings on the nature of cultural selection (i.e.: general intelligence rising over the past century)

I think general intelligence has most likely decreased over the last century, while knowledge has increased.

There is general scientific consensus on this, as it has been studied for quite some time. Take Robert W Howard as a good starting point. There are many factors like declining motivation at play but generally it is rising