[extropy-chat] Why Progress Might Slow Down

[CurtAdams at aol.com]

In a message dated 11/4/03 7:18:49, rhanson at gmu.edu cites:

>http://www.dienekes.com/blog/archives/000354.html
>
>The secular rise in IQ: Giving heterosis a closer look
>by Michael A. Mingroni, forthcoming in Intelligence
>
>Although most discussions today start from the assumption that the secular
>rise in IQ must be environmental in origin, three reasons warrant giving the
>genetic phenomenon heterosis a closer look as a potential cause. First,it
>easily accounts for both the high heritability and low shared environmental
>effects seen in IQ, findings that are difficult to reconcile with
>environmental hypotheses. 

Um, no, that's not right.  Heterosis affects are generally *not* highly 
heritable.  For example, take a individual with an AA genotype (inbred,
poor phenotype) and cross with a BB genotype (same).  All offspring are
AB (outbred, good phenotype).  By contrast, if a healthy AB mates with
a healthy AB, half the offspring are AA and BB, ie, inbred-like, and poor,
genotypes.  So *better* parents have *worse* offspring - the opposite
expected from high heritability.

>Second, numerous other highly heritable traits,
>both physical as well as psychological, have also undergone large secular
>changes in parallel with IQ, which is consistent with the occurrence of
>broad-based genetic change like heterosis. 

But, also with environmental change.  Feed people more, they mature
earlier and grow taller.   That's definitely an environmental change,
even though height is a highly genetically heritable trait.

>And third, a heterosis hypothesis
>for the trend can be tested in several straightforward ways. The paper also
>provides a hypothetical example, based on data from a real population,
>of how heterosis can result from demographic changes like those that have
>taken place throughout the developed world in recent history and shows that 
under
>certain conditions, even a small demographic change could cause large
>genetically based phenotypic changes.

The last, and most serious strike, is that heterosis effects could have no
ongoing effect in countries of recent settlement, such as the US and Canada.
You need generations of strong isolation of small villages to get much 
inbreeding
and the US and Canada were founded by individual or small family migrants from
the getgo.  There was never any inbreeding to dispose of.