From: Lee Corbin (lcorbin@tsoft.com)
Date: Thu Oct 03 2002 - 01:58:19 MDT
Rafal writes
> ### Regression to the mean is a natural by-product of recombination of
> recessive traits - the super-smart are so smart because they have the
> luck of being homozygous for some IQ-enhancing recessive genes, but for
> any single person the exact combination of such genes is likely to be
> different than in their super-smart mate. As a result, the offspring
> will be heterozygous for many of the traits that made their parents
> super smart, and the IQ will be on average lower than the parent IQ.
Thanks much for that explanation. I had always supposed
that it was entirely an environmental effect. Say one had,
hypothetically, a collection of giraffes and decided to
perform some eugenic experiments to maximize neck length.
We can readily suppose that although (perhaps) predominantly
determined by genes, environment still can play a significant
role. Some giraffes, for example, will by luck have a superior
intra-uterine environment in which to develop, and by chance
receive extra nutrition or exercise at the most fortuitous moments.
To clinch that argument, suppose that all the giraffes of my
example were identical twins or clones, and that *all* the
variation in height was due to environment. One would certainly
expect, then, that regression towards the mean via my mechanism
would ensue.
Therefore, much as I appreciate your argument, (and as much as it
is very provocative mathematically), I still contend that regression
to the mean also obtains from environmental effects.
> E.g.
> Pat AAbBCCdd x mat aaBBcCDD will produce offspring aAbBcCdD, aABBcCdD,
> aAbBCCdD, aABBCCdD. Capitals denote the alleles which if homozygous will
> increase IQ. Only one of the filial genotypes will have a combination of two
> homozygous high IQ alleles (=same as parents). You do not need a large
> number of loci for this effect to be apparent.
Nothing could be clearer than your example.
> The argument for the dysgenic effect of high-IQ emigration on the remaining
> population is however independent of the above - if you kill the smartest
> 25% of the population (or remove them from the group by emigration), the
> frequency of high-IQ alleles will be lower.
This is so obvious that I want to engage in speculations as
to *why* people so resist the notion that one could in
principle breed for intelligence in laboratory mice, in
dogs, or in humans. And just as certainly, one could
breed for stupidity, which could also occur naturally as
in Spike's example of small towns which, hypothetically,
lose their most intelligent people in each generation but
don't lose any of their least intelligent people.
> In the example above, try to see the frequency of F2
> (second-generation filial) and subsequent generation
> phenotypes from the matings between the first three
> genotypes (the fourth moved to Palo Alto).
So your F2 will obtain from every combination of mating
between
aAbBcCdD
aABBcCdD
aAbBCCdD
aABBCCdD
which you obtained easily from your original AAbBCCdd x aaBBcCDD.
So your F2 will obtain from every combination of mating between
them. Here is what I think the F2 look like.
aAbBcCdD x aAbBcCdD = aabbccdd aAbBcCdD aAbBcCdD AABBCCDD
aABBcCdD = aabBccdd aAbBcCdD aABBcCdD AABBCCDD
aAbBCCdD = aabbcCdd aAbBcCdD aAbBCCdD AABBCCDD
aABBCCdD = aabBcCdd aAbBcCdD aABBCCdD AABBCCDD
aABBcCdD x aAbBcCdD = aaBbccdd aABBcCdD aAbBcCdD AABBCCDD
aABBcCdD = aaBBccdd aABBcCdD aABBcCdD AABBCCDD
aAbBCCdD = aaBbcCdd aABBcCdD aAbBCCdD AABBCCDD
aABBCCdD = aaBBcCdd aAbBBCdD aABBCCdD AABBCCDD
aAbBCCdD x aAbBcCdD = aabbCcdd aAbBCCdD aAbBCCdD AABBCCDD
aABBcCdD = aabBCcdd aAbBCCdD aABBCCdD AABBCCDD
aAbBCCdD = aabbCCdd aAbBCCdD aAbBCCdD AABBCCDD
aABBCCdD = aabBCCdd aAbBCCdD aABBCCdD AABBCCDD
aABBCCdD x aAbBcCdD = aaBbCcdd aABBCCdD aAbBCCdD AABBCCDD
aABBcCdD = aaBBCcdd aABBCCdD aABBCCdD AABBCCDD
aAbBCCdD = aaBbCCdd aABBCCdD aAbBCCdD AABBCCDD
aABBCCdD = aaBBCCdd aABBCCdD aABBCCdD AABBCCDD
Is it really so simple as this, or have I made a conceptual error
here? It's rather astonishing that 1/4 of the entire F2 is
radically "smarter" than their grandparents, but, perhaps not,
given the original distribution of capital letters. One also
easily sees that if the right-most three columns left town,
a lot of good genes would go with them.
Lee
> A phenotype will depend on the total number of homozygous capitals
> - you will get some phenotypes smarter than the paternal generation
> but the overall frequency of high-IQ will be lower with each
> generation where you remove the top achiever.
>
> Rafal
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