From: Eliezer S. Yudkowsky <sentience@pobox.com>
>phil osborn wrote:
>>
>> First, it's nature AND nurture, obviously, else cats and mosquitos would
>> both have human intelligence. What Burt did was to heavily tilt the
balance
>> of evidence to please the British aristocracy. As I recall, he concluded
>> that about 80% was heredity, when in fact the data indicated more like
>> 50/50.
>
>I beguess that it's almost exactly 50/50, or a Gaussian curve centered
>very precisely on 50/50 and without too large a standard deviation,
>either.
Studies on twins trace approximately two thirds of IQ to genetic variation.
From:
http://www.cycad.com/cgi-bin/Upstream/Issues/psychology/IQ/bouchard-twins.ht
ml
General intelligence or IQ is strongly affected by genetic factors. The IQs
of the adult MZA twins assessed with various instruments in four independent
studies correlate about 0.70, indicating that about 70% of the observed
variation in IQ in this population can be attributed to genetic variation.
Since only a few of these MZA twins were reared in real poverty or by
illiterate parents and none were retarded, this heritability estimate should
not be extrapolated to the extremes of environmental disadvantage still
encountered in society. Moreover, these findings do not imply that traits
like IQ cannot be enhanced. Flynn [35], in a survey covering 14 countries,
has shown that the average IQ test score has significantly increased in
recent years. This increase may be limited to that part of the population
with low IQs [36]. The present findings, therefore, do not define or limit
what might be conceivably achieved in an optimal environment. They do
indicate that, in the current environments of the broad middle-class, in
industrialized societies, two-thirds of the observed variance of IQ can be
traced to genetic variation.