Re: Intelligence on the X chromosome

Hugh Gibbons (
Wed, 28 Aug 1996 23:20:11 +0000

Jef Bateman wrote:
> Forgive if this was already addressed, but to what extent are people
> accepting this research in the first place? I have not read any
> informed, critical evaluations of the issue itself.
> Even if the research were well-done, what they are asking us to
> believe is rather implausible. The way I see it, we would have to accept
> the following assertions:
> 1. Intelligence is a single discrete quantity.
> 2. This quantity can be measured.
> 3. This quantity is genetically based.
> 4. The amount of genetic material needed to "code" this quantity

There is, as you point out, not a clear picture of the evidence.
All our measures of intelligence are clouded by such factors as
inaccurate gauges, biases, etc. But it's fair to argue that
such indicators as student achievement scores, IQ tests etc.
are to some degree affected by native intelligence,
among many other factors. If you take at face value that
the scores are to some degree reflective of intelligence
(whatever that is) you have a clear difference that may
be explained by some intelligence-affecting factors could
be on the X-chromosome. I hope that satisfies your first two

Obviously genes affect intelligence. We're not trying to show
absolute causation, just an influence. Certain genes cause
severe defecits in intelligence. Some minimum collection of
"correct" genes must be necessary to have a normally working
human brain. Any flaw in the genes is likely to show up as
a mental disability (though perhaps small). Certain novel
genes may cause a few people to have extraordinary abilities.

As for #4, the X chromosome is quite large, and contains a
a lot of genes. It would be a great surprise if some of
them did not affect brain development or function.

Hugh Gibbons