We might also consider that the default assumption here is that this would be a well-functioning society. Well-functioning enough to reproduce in any kind of stable fashion. I don’t think it would be. If you took all the brightest people–even assuming they are socially well-adjusted in a broad society–and made a society out of only them, you wouldn’t have many followers. To properly implement a successful eugenics program, you’d need to have fairly well-enforced structure that creates hierarchies in a world where everyone is an alpha genius. Too many chiefs; too few Indians? Who does the drudge work in such a society before Rosie the Robot is invented?
A second item worth mentioning is (idle speculation) on whether or not physical ability and mental agility are at odds, genetically. Dumb jocks; weakling scientists. If it turns out there is a genetic underpinning to “really smart or really fast, but not both” then you have a second problem. Suppose, for instance, that testosterone-like hormones drive physical prowess but at the expense of brain prowess, and a given evolutionary environment has to make a trade for one trait or the other, but not both.
One of the things that Mensa plays up is that their members are in all walks of life. There are rocket scientists in Mensa, and also janitors, for instance. Now, I’ll grant you that IQ tests will only measure certain kinds of intelligence, but I’d say that having a high intelligence doesn’t necessarily mean that the person will be a leader. Some are content to be followers. I would imagine that there might be fewer pure drudge jobs, and that each person would have to clean up after him/herself more, and also that the general drudge work would be rotated.
I can only imagine with horror a society made up of Mensa members. I have gone to a few social functions (as well as their Annual Gatherings) a few times and I have to say, these people may be smart, but dear God, their social development is stunted. They all think they are eighty times smarter than they are; they have virtually no social graces, as a rule, are arrogant, won’t shut up. interrupt other people constantly to insert their (often wrong) pearls of wisdom, and are generally a pain in the ass to be around. They do mate with each other occasionally because no one else will have them, but in a colony of nothing but Mensans, everybody would be dead within a week.
This is very odd. The children of PhDs in physics aren’t all that likely to get PhDs in physics, and thus wouldn’t be working at Los Alamos. Second, why would they stay?
Third, you have not demonstrated correlation between high intelligence and expert bridge playing. Perhaps the people you played with selected themselves for being good, and most of the genius population are whatever the bridge equivalent of potzers? I’ve played bridge at MIT and Bell Labs, for fun, and I assure you we were nothing special.
Mensa membership however does not represent the premise very well. None of the very smartest people I have met have been Mensans; they feel no need to join such a group. Joining Mensa selects for those who also have some other need in their life that is not otherwise being met.