There probably is no "correct" answer.

No shit. The analysis of the development of humanity is far more complicated than global climate analysis is.

Not only is humanity as a whole capable of real-time adaptation to change, something approached in the rest of nature only by bacteria, but in no other species can a few members, or even a single member, alter the course of history by his or her actions.

We can draw some general conclusions, or make educated guesses, but

Hari Seldon was full of beans. In real life, there's hundreds of "Mules" born every year.

I think humans stopped being selected for intelligence once they settled down and started farming.

I would agree with that.

If we could magically bring a few hundred Cro-Magnon babies to our time and raise them with urban families, I wouldn't be surprised if their average IQs were a few percent higher than our present population's.

Probably. People might even be surprised if you raised a Neanderthal baby in our current society. I think they've gotten a bit of a bad rap.

For the same reasons, I believe average human intelligence is on a path of decline. At best, we may be as smart now as we're ever going to get.

Biological-only intelligence, maybe. But we're past that, now. Humans can lift a lot bigger loads now than a caveman could, but we aren't as strong.