[hodwik2]

>"Heritability of traits can be measured by twin studies."

No, correlations between traits can be measured in twin studies, but they do not prove a causal link.

In the realm of intelligence, it could be (and I would argue) that looking like a nerd generally proceeds becoming one. People become social outcasts, and then become intelligent as a defense mechanism. That is,once in that nerd social caste, a greater percentage of people will find themselves using their brains more often. As a result, they get smarter, and score better on IQ tests.

Because twins are liable to look the same way, have the same temperament, same physique, etc. they are liable to be pushed into the same sorts of social groups, and as a result the same sorts of interests, ultimately pushing their IQs up or down together.

This would not mean that IQ is heritable, but that traits which can have a forcing effect on nurture (and thus IQ) are heritable.

[Throwaway585250]

How about torsion dystonia? Increased IQ can be observed before the onset of the disease, even when matched to comparable members of the same population.

What evidence would falsify your position?

[hodwik2]

A few things on torsio dystonia.

One, Torsion Dystonia could just as easily be effecting something else which effects IQ.

Two, the studies on Torsion Dystonia decided to only study people who were not showing symptoms. This means they were selecting around heredity, since those who show symptoms and those who don't were not divided on gene expression -- there is only one allele in play as far as we know.

Three, the study was 14 persons. Removing a single person from the sample could have swung the data to say the opposite.

[bordercases]

Point 3 is weak without a quote of the variance or other such notions of spread.