They were now their own unavoidable experiment, and were making themselves into many things they had never been before: augmented, multi-sexed, and most importantly, very long-lived, the oldest at that point being around two hundred years old. But not one whit wiser, or even more intelligent. Sad but true: individual intelligence probably peaked in the Upper Paleolithic, and we have been self-domesticated creatures ever since, dogs when we had been wolves. But also, despite that individual diminution, finding ways to accumulate knowledge and power, compiling records, also techniques, practices, sciences2312 by Kim Stanley Robinson (goodreads.com)
possibly smarter therefore as a species than as individuals, but prone to insanity either way.
I have almost finished listening to this on Audible.