Re: Brain size, IQ

Bryant (
26 Aug 1996 14:35:36 -0600

In article <>,
Len Piotrowski <> wrote:
>In article <4vqusf$> (Bryant) writes:
>>As Dawkins points out in his _Extended Phenotype_, the association of
>>larger cranial capacity and apparently increased intelligence in the Homo
>>lineage suggests (demands) heritability for brain size in past human and
>>proto-human populations. This is, hopefully, not controversial.
>I am not familiar with Dawkin's hypothesis, but you would be mistaken about
>the uncontroversialness of your statement.

What's controversial about the notion that cranial capacity was heritable
during human evolution? How else do you explain the dramatic changes in
head size through time, as evidenced in the fossil record of our ancestors?

Heritability means, evolutionarily, "not fixed." That is, genetic or
allelic variability is responsible for phenotypic variability for a given
trait. Once an allele is fixed in a population, heritability is zero,
because everybody has the same allele for that trait, and phenotypic
variation in that trait cannot be accounted for genetically.

>The evolutionary significance of altered developmental ratios for humans,
>seems to affect the sexes differently. Females appear to experience prolonged
>developmental growth with respect to males, thus apparently increasing the
>time and development of the neural net. A byproduct of this developmental
>retardation may just be something measurable by the human IQ test. Who knows?

I don't follow this. Sorry. Could you reword this?