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As I explained in a previous post, a popular belief is that the Flynn Effect disproportionately impacts the lower parts of the bell curve.  The reason this theory is so popular is because hypothesized causes of the Flynn Effect (increased schooling, better nutrition) are assumed to help primarily the most disadvantaged people, but have diminishing returns as you move up the scale.  It’s also popular because it nicely explains why past generations had so many impressive scientists, thinkers and writers despite the average test score being so low.  And for culturally biased tests like the SAT, the Flynn Effect is indeed much smaller at the high end.  The percent of all American 17 years old (not just those who finish high school) capable of scoring at the highest levels on the Verbal SAT has not been increasing according to the book “The Bell Curve”, even though at the low end of the distribution, literary rates have been skyrocketing over the 20th century.

However when it comes to one of the best and most culture fair tests we have (the Raven Progressive Matrices), this theory absolutely collapses.  In the previous post I talked about the dramatic Raven Flynn Effect in the brightest 10% of British men over the 20th century.  But perhaps I wasn’t looking high enough.  Perhaps the Flynn Effect disappears for the top 1%, or the the top 0.1%.  Fortunately, the always resourceful James Flynn, long ago found the data.  If you look at table 18 of a post by blogger Meng Hu, you can see Flynn’s data.  What it shows is that in the Netherlands (where Raven scores jumped the equivalent of 21 IQ points in 30 years), getting even extremely high scores became a lot more common.  By equating the changing frequency to the IQ distribution (mean 100, SD 15) we see that an IQ of 130 on the older norms equaled an IQ 110 on the newer norms.  An IQ of 140 on the older norms equals an IQ of 120 on the newer norms, and an IQ of 150 on the older norms, equals an IQ of 130 on newer norms.  So it seems the entire distribution increased by about 20 points from 1952 to 1982, including the extremely brilliant.

So what has caused these massive gains in such a short span of time? [UPDATE June 22/2014: I was informed in the comment section that the Flynn Effect gains among the gifted may have been theoretical rather than actually observed data, in which case, my above analysis is circular speculation].  James Flynn equated the older and younger generation on schooling and found that changes in education explained only about 1 IQ point of the massive rapid gains.  Virtually nothing. And given the relatively high correlation between IQ and schooling (within generations), one can assume that people above IQ 150 were already finishing high school at high rates in 1952 so schooling seems an unlikely cause, especially for a test as seemingly culture fair as the Raven.  So that brings us to Richard Lynn’s nutrition hypothesis which argues that 20th century nutrition has been increasing both intelligence and height.  This theory is especially compelling when one consider that the unusually large Flynn Effect the Dutch enjoyed (7 points a decade!) is nicely paralleled by unusually rapid height gains over the same span of time.

Some interesting quotes from an article in USA Today:

The Dutch were not noted for their height until recently. It was only in the 1950s that they passed the Americans, who stood tallest for most of the last 200 years, said John Komlos, a leading expert on the subject who is professor of economic history at the University of Munich in Germany. He said the United States has now fallen behind Denmark.

So, like the Raven IQ gains, the height gains seem to have taken off in the 1950s

Many Dutch are much taller than average. So many, in fact, that four years ago the government adjusted building codes to raise the standards for door frames and ceilings. Doors must now be 7-feet, 6 1/2-inches high.

So like the Raven IQ gains, the height gains have been very strong at the highest levels.

In 1848, one man out of four was rejected by the Dutch military because he was shorter than 5-foot-2. Today, fewer than one in 1,000 is that short.

This is an astonishing statistic.  It suggests that height among the Dutch has increased by 3.8 standard deviations since the 19th century.  Does that imply that biological intelligence has increased by 57 IQ points?!! Obviously the nutrition theory is wrong to imply such absurd conclusions? Not so fast. Two points must be understood:

1) Primarily NON-VERBAL intelligence is affected by nutrition.  Even the malnourished mind preserves virtually all its verbal-numerical intelligence.  And this is not because these are crystallized skills acquired before the onset of malnutrition.  Even when malnutrition occurs before birth, the ability to acquire verbal-numerical skills is virtually unscathed and these are the abilities that determine cultural achievements.  Non-verbal disabilities are relatively invisible. So even if overall intelligence had increased by 3.8 SD, the increase would be extremely lopsided, with non-verbal IQ increasing much more, and verbal-numeral IQ hardly increasing at all.  It’s unclear whether one should expect a 3.8 SD increase in overall IQ (verbal + non-verbal), or a 3.8 SD increase in just non-verbal IQ, in which case overall IQ would be much less increased.  But either way, verbal-numerical ability (the building blocks of culture) would be virtually unchanged.

2) The reason height gains are relevant is that they parallel gains in brain size (and probably other properties of the brain too).  But it’s unlikely that a 3.8 SD gain in height implies a 3.8 SD gain in brain size, since brain size probably has a much higher genetic floor than height does, which is why people of extremely short stature often appear to have big heads.

Lastly, the paradox of huge Raven gains (even at the high end) while no comparable high end gains on the Verbal SAT is resolved.  Verbal-numerical ability is virtually untouched by nutrition, though the rise in education has improved crystallized forms of such skills at the low end (literacy rates) but not the high end because the gifted have always been educated.  By contrast nutrition improves the ENTIRE distribution, hence even the gifted show huge Raven Flynn Effects. As for the Math SAT, that’s a mix of Verbal-numerical ability and NON-VERBAL problem solving, so it shows more high end gains than the Verbal SAT, but less than a pure non-verbal culture reduced test like the Raven.