Other thought experiments are certainly possible, but mine is about the stated gamble, in which you cannot predict. That's what's meant by "unshared environment

Other thought experiments are certainly possible, but mine is about the stated gamble, in which you cannot predict. That's what's meant by "unshared environment", it's poorly named, the environment you talk of is "shared environment". As I said, I don't know that this is true in the real world, but I don't think it wildly implausible. (Maybe tortured mad artists are a better example than nerds.) Tay-Sachs is the first example I know about, of some genetic strain of humans being deliberately bred out of existence. Phrased like that I think the idea would alarm many people. But it has not. (I should remind myself more of the details of this story.) Thought experiments aside, note that it's not obvious we need a single new mutation to make much smarter people. We just need the shuffling of the deck to place more of the existing + variants into one body. This will obviously be the goal of embryo selection, and I think would also be the goal of explicit editing. I'd wager that many more of the Nobel-sized brains alive at the end of this century (and the next) will owe their existence to one of these kinds of engineering, than to population growth.