Re: Oh, those gaussians (Was: Twin Studies)

J. R. Molloy (
Sun, 22 Aug 1999 08:54:18 -0700

From: Eliezer S. Yudkowsky <>

>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
>> 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,

Studies on twins trace approximately two thirds of IQ to genetic variation.

From: 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.