[extropy-chat] Why Progress Might Slow Down

[Robin Hanson]

On 11/4/2003, Curt Adams wrote:
> >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.

Maybe you should read the paper first?  The topic is average changes, not
the change in each possible case.

> >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.

We don't actually know how much nutrition can account for height 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.

You might be right, but I don't think we have the data to support your claim
with any confidence.



Robin Hanson  rhanson at gmu.edu  http://hanson.gmu.edu
Assistant Professor of Economics, George Mason University
MSN 1D3, Carow Hall, Fairfax VA 22030-4444
703-993-2326  FAX: 703-993-2323