Genius as distinct from high IQ

From A theory of Ashkenazi genius: intelligence and mental illness by Emil O. W. Kirkegaard.  

Kirkegaard is exploring the association between genius and mental illness.  It is a long debated topic.  I am more interested in a related phenomenon, the burst phenomenon of population genius.  Why do we repeatedly see bursts of genius at a population level which are distinct from before and after periods?  These burst can be from 50-150 years in length (i.e., multigenerational.)  

I accept that genius, if defined simply as a point above some level on an IQ distribution, can have a population and biological component.  In other words, in addition to IQ being reasonably strongly hereditary, different populations have different IQ means and sometimes might have different standard deviations which imply that some populations will have a higher percentage of their population above the defined IQ level to warrant as genius.

But why do we see instances where, in a relatively brief time span, a stable population suddenly demonstrates a much higher degree of genius than at other times, before or after?

Candidates for such flowerings would include

Scotland 1700-1850

Greece 550-400 B.C.

Northern Italy 1300-1550

Netherlands 1450-1700

Western European Ashkenazi Jewry 1600-1850

Eastern European Ashkenazi Jews in America 1900-2000

In some instances, changes in genetic composition might possibly be argued but that seems shaky ground to me.  

My general disposition is that these bursts of development are the product some base biological capacity for higher IQ distributions in combination with shorter term reductions in some key constraints, usually social, cultural, material, technological, etc.  The constraints are reduced (for whatever reason) and the latent capacity for genius manifests.  Eventually the old constraints return or new ones emerge and the population level manifestation of genius falls.

A variation of this is to view populations as having Supply and Demand curves of genius.  The Supply may in fact be heavily driven by genetic potentialities.  However, if circumstances constrain Demand, then actual manifested genius will be below the potential.  

Ashkenazi Jews in Eastern Europe or Scots in Scotland may have stable and high genetic dispositions towards genius but if the demand is low because of constraining social hierarchies or structures (serfdom) or material want (low wealth), etc.  then the intersection of Supply (genetics) and Demand (materials and social constraints) curves will result in a lower manifestation of genius than possible.  When those Demand constraints are relaxed (spread of Classical Liberal norms, industrial revolution, increased tolerance, etc.) then the intersection of Supply and Demand shifts upwards and outwards.  

But all that is speculative.  I was interested in this section of Kirkegaard's argument which begins to hone in on the definition and measurement of genius as distinct from simply high IQ.

I want to put together a theory to explain a putative phenomenon: Ashkenazi Jews have more geniuses relative to non-Jewish Europeans (gentiles) than one would expect based on their average intelligence of about 110 IQ. This hasn't been strictly shown mathematically, but I think it is true. We can do a rough estimate using the interactive tail effects tool here. We fill in the approximate number of European Americans and Ashkenazi Americans. I used 204 and 5.5 million. Then we fill in the approximate mean and SDs of IQ, I used 100/15, 110/15. Then we have to guess at a threshold for resulting in a genius of some sort. It is well knowing that there is more to genius than simply being very smart. The SMPY and Terman samples didn't produce many geniuses despite sky-high IQs, the latter even missed two Nobel prize winners. But let's ignore this, and say the threshold is 140. Using that, we get this result:

Click to enlarge.

So among the Americans who are regular Europeans or Ashkenazis and who have 140+ IQ, 86% are gentiles, and so 14% are Ashkenazis. However, looking at US Nobel prize winners, Ashkenazis appear to be about 33%. Thus, according to our crude modeling, there's something like twice as many Ashkenazi geniuses than expected, some other factor is at play making them more likely to become geniuses. Mind you these numbers are all approximative.