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NancyLebovitz comments on Q&A with Harpending and Cochran - Less Wrong
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That may be the case, but I still don't find the explanation satisfactory from the point of view of the classic general intelligence theory (not that I have a better alternative, though).
To clarify, the traditional theory of general intelligence, which is taken as a background assumption in most IQ-related research, assumes that general intelligence is normally distributed in the general population, and any reasonable measure of it will be highly correlated with IQ test scores (which are themselves artificially crafted to produce a normal distribution of scores). Moreover, it assumes that people whose intellects stand out as strikingly brilliant are drawn -- as a necessary condition, and not too far from sufficient -- from the pool of those whose general intelligence is exceptionally high. Now, if the scores on IQ tests are rising, but there is no visible increase in outstanding genius, it could mean one or more of these things (or something else I'm not aware of?):
We're applying higher criteria for genius. But are we really? Has the number of people at the level of von Neumann, Ramanujan, or Goedel really increased by two orders of magnitude since their time, as it should have if the distribution of general intelligence has simply moved up by 2SD since their time? (Note that for any increase in average, ceteris paribus, the increase in the rate of genius should be greater the higher the threshold we're looking at!)
The average has moved up, but the variance has shrunk. But this would have to be implausibly extreme shrinkage, since the average of IQ scores today is roughly at the z-score of +2 from two generations ago.
The modern culture is making common folks smarter, but it drags geniuses down. I believe there might be some truth to this. The pop culture everyone's supposed to follow, however trashy, has gotten more demanding mentally, but true intellectual pursuits have lost a lot of status compared to the past. Still, such effects can't explain the severity of the effect -- remember, the Flynn increase is greater than the difference between borderline retardation and being above average in the way the scores are used for diagnostics!
The IQ scores say a lot about people who are average or below average, but not much about smart people. This seems like the most plausible option to me, and the only one compatible with evidence. But this means that the standard model based on the normal distribution is seriously broken when it comes to the right side of the distribution, and it also makes the results of many heritability studies much more murky.
All in all, the situation is confusing, and unlikely to get clearer in the near future.
It's conceivable that there are institutional barriers to genius expressing itself-- partly that there really is more knowledge to be assimilated before one can do original work, and partly that chasing grants just sucks up too much time and makes it less likely for people to work on unfashionable angles.
Still, it's not like historical geniuses all grew up as pampered aristocrats left to pursue whatever they liked. Many of them grew up as poor commoners destined for an entirely unremarkable life, but their exceptional brightness as kids caught the attention of the local teacher, priest, or some other educated and influential person who happened to be around, and who then used his influence to open an exceptional career path for them. Thus, if the distribution of kids' general intelligence is really going up all the way, we'd expect teachers and professors to report a dramatic increase in the number of such brilliant students, but that's apparently not the case.
Moreover, many historical geniuses had to overcome far greater hurdles than having to chase grants and learn a lot before reaching competence for original work. Here I mean not just the regular life hardships, like when Tesla had to dig ditches for a living or when Ramanujan couldn't afford paper and pencil, but also the intellectual hurdles like having to become professionally proficient in the predominant language of science (whether English today or German, French, or Latin in the past), which can take at least as much intellectual effort as studying a whole subfield of science thoroughly.
So, while your hypothesis makes sense, I don't think it can fully explain the puzzle.
It could also be communications.
Many high intelligence situations involve disorders that also have as an effect anti-social behavior. Academia is highly geared against this in some cases going so far as to evaluate people's chances for success in a PhD based on their ability to form working relationships with a peer group during their MSc. Travel is easier and correspondence is far more personal.
Would the mathematicians of the past have been as interested in this model? Perhaps some of them were the type of people that were happy to correspond by mail but found communicating face to face awkward. This wasn't a big barrier to success in the past, but it is very difficult in modern academia (particularly with most positions in most fields being teaching + research).
Far enough, and I'm not even sure the "more knowledge required" is that strong an argument for some parts of math.
A scary possibility is that there are fewer people at the far right end of the bell curve. I have no idea what could case that effect, but we don't know what makes for genius of the sort which does significant creative work.
It's conceivable but unlikely that teachers' ability to recognize extraordinary minds has declined.
Perhaps genius requires extraordinary effort, which is only worthwhile if you already have nothing to lose. So maybe the hardships and obstacles that previous highly intelligent people faced actually contributed to their eventual success.
There are still plenty of poor people, so lack of hardship doesn't seem to be the problem.
IIRC, there's a theory that you get more genius when political entities are small and competing-- hence the Renaissance. However, that's generalizing from one example-- any clues plus or minus for the theory?
There are always people with nothing to lose-- it may be less common to have elites with something to win.