Renowned pychometrician Charles Murray has given us, in The
Inequality Taboo, a concise summary of the most current science on
group differences in IQ and other measures of capability. Most of it
is not surprising to anybody who has been following the actual science
rather than press accounts severely distorted by the demands of
political correctness.
There is some new information here, however, and perhaps the most
interesting bit is that turns out to be much less to the Flynn effect
than meets the eye. The Flynn effect is the long-term rise in average
IQ scores recorded since IQ began to be measured in the early 20th
century. Advocates of the view that IQ is unimportant or meaningless
have seized on the Flynn effect to argue that IQ is either (a) a
statistical artifact, or (b) almost entirely environmentally driven
(and thus can presumptively be increased by correct social
policy).
Murray’s news is that the Flynn effect is not being driven by a
rise in average g, the measure of general mental ability that accounts
for over 50% of variance in almost all kinds of mental aptitude tests.
Since Spearman discovered the ‘g’ statistic, almost all psychometricians
have accepted that IQ is interesting precisely because it is a good
approxmation of g. Thus, the Flynn effect is basically a mirage —
it’s taking place in the noise, not the signal.
I’m not entirely sure what this means yet, and I don’t believe
Murray or other psychometricians have gotten to the bottom of it
either. But at minimum, it’s very suggestive that IQ differences are
either genetic or driven by environmental factors over which we have
little control. Spearman’s g, in particular, is notoriously
intractable. It is highly heritable according to separated-twin
studies. And while there is good evidence that it can be lowered from
its ‘natural’ genetic level by unfavorable environment (such as poor
childhood nutrition), it apparently can’t be raised by a favorable
one.
Indeed, Murray reports in a footnote evidence from a study in
Denmark that the Flynn effect has leveled off since the early 1990s.
Thus, it may be that we have already maxed out the effects of wealth
and better nutrition on the both the g and non-g components of IQ that
we can manipulate.