From: Rafal Smigrodzki (rms2g@virginia.edu)
Date: Thu Oct 03 2002 - 13:39:11 MDT
Charles Hixson wrote:
> Rafal Smigrodzki wrote:
>
>> Damien wrote:
>>
>>
>>> At 06:26 PM 10/2/02 -0400, Rafal wrote:
>>>
>>>
>>>
>>>> ### 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
>>>>
>>>>
>>> ...
>>
>> ### You got it just right - the regression is to the mean of the
>> *remaining*, not the initial population. E.g. if you remove persons
>> above IQ 100, the IQ of the breeding population will drop to 89.88
>> (see http://www.psychstat.smsu.edu/introbook/normal.htm for the
>> calculation applet), and the regression will be towards 89.88, for
>> both the remaining parents with IQ 100 and the ones below 89.88.
>>
>> Rafal
>>
>>
> It is, however, a complex trait rather than a simple trait. There is
> no reason to believe that all "smartness enhancing" genes are mutually
> reinforcing, and considerable reason to disbelieve that.
### Indeed you are right. The 89.88 figure was obtained under the assumption
that the traits are inherited independently, their influences are simply
additive, and any systematic biases cancel out. The exact average IQ of such
divided population cannot be calculated - you would need to actually do the
experiment to get the correct number. Still, from general principles we can
get estimates which will in most cases be close to the truth - because with
the large number of unlinked genes, systematic biases *do* cancel out.
Rafal
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