April 06, 2014
Genetic Variant Quadruples Risk For Low IQ

Cardiff University researchers have found another genetic variant that plays a role in determining IQ.

They discovered that children with two copies of a common gene (Thr92Ala), together with low levels of thyroid hormone are four times more likely to have a low IQ. This combination occurs in about 4% of the UK population.

The post is by Oxford ethics prof Julian Savulescu. He points out that while doing IVF (in vitro fertilization followed by implantation) it would be fairly easy to screen for this and other genetic variants to select which embryo to implant. He finds it appealing to select against thisThr92Ala genetic variant because it would selective boost the intelligence of lower IQ folks. Therefore it would reduce inequality.

Another common objection to enhancement is that it would create inequality, allowing the rich to get smarter and pass on these benefits to their children. In this case, however, the interventions would only benefit those with an IQ of 70-85 so it would in fact reduce inequality. This is a strong argument in their favour.

I certainly think that selecting against passing 2 copies of this genetic variant to offspring is worthwhile and should be started sooner rather than later. But I do not think the legality of using genetic info for embryo selection should be weighed based the expected impact on equality of outcomes. It seems very short-sighted to oppose raising the intelligence of the children of very bright people in a quest for greater equality of outcomes. We all benefit from the higher levels of productivity of very bright scientists, engineers, managers, and scholars.

Already lots of genetic markers associated with intelligence difference are known and so the knowledge already exists to allow pre-implantation embryo selection to be done to boost intelligence. What is so far missing (at least to my knowledge): availability all those genetic markers in a test service for fertility clinics.

We still need more genetic markers for intelligence and also genetic markers for personality differences. I am hoping that when prospective parents gain the ability to select genetic variants for their offspring they will opt for more conscientiousness and that they won't go for genetic variants that create psychopaths. But I am uncertain what sorts of children psychopaths and border line psychopaths will choose to create. We might see the human race divergence into incompatible personality types that eventually cause societies to schism into separate new societies.

Share |      Randall Parker, 2014 April 06 08:46 PM 

Radford Neal said at April 6, 2014 10:17 PM:

Does anyone have any idea why this apparently deleterious gene variant occurs at a frequency of about 20% in the UK population (so that 4% have two copies)? Could it just possibly be that it confers some unknown advantage? It might be a good idea to find out before elminating it from the gene pool...

Engineer-Poet said at April 7, 2014 11:53 AM:

It could also be that it's being selected out and is on its way to extinction.  Testing DNA of burials from a few dozen generations ago, as well as native vs. migrant populations, would clarify that.

Radford Neal said at April 7, 2014 2:43 PM:

If it's being selected out, it must have been even more common in the past, presumably due to some substantial advantage. It may be that this advantage is no longer relevant to modern life, but I wouldn't want to assume that without knowing what it was.

Engineer-Poet said at April 8, 2014 6:21 AM:

If it's being selected out, it was probably an older variant which is losing share to the newer, higher-IQ allele.

Not all losing genetic variants have, or ever had, survival value.

Tj Green said at April 8, 2014 5:45 PM:

Our increasing knowledge and technology is moving us away from life`s battlegrounds so a loss of genetic variation would not lead to our extinction as it would for other species.

Randall Parker said at April 8, 2014 8:52 PM:


I wondered that as well. I would like to see a geographical distribution. I wonder if iodine deficient people function better with it.

spindizzy said at April 9, 2014 3:18 PM:

Genetic variation is being lost all the time due to differences in reproductive rates among subpopulations. For some reason, people only seem to care about this when the issue is framed in eugenic terms.

Latias said at April 9, 2014 4:16 PM:

So you posted this without any refer to the work by the scientists?

Yes, almost indubitably, those with a low IQ have a shitty quality of life.

destructure said at April 9, 2014 4:50 PM:

Randall's desire to hack away at DNA before it's fully understood has consistently been one of the few areas of disagreement between us. I agree with Radford that if it occurs at 20% it probably confers an advantage. And I disagree with others who assume without any basis that it's being selected out. Who says it's being selected out? Maybe it's increasing? Maybe it's in equilibrium? You don't know.

I would however suggest a parallel with sickle cell or tay sachs. Two copies of sickle cell gives you the disease but one copy provides resistance to malaria. Two copies of the tay sachs gene gives you the disease but one copy makes you smarter. It's not necessary to screen out every embryo carrying the gene. You only want to screen for embryos carrying TWO copies. If screening becomes standard / universal then it may well be that everyone might be better off carrying one copy of the gene. Simply screen out embryos carrying none or two which would be half of them.

Latias said at April 9, 2014 5:09 PM:

I am going to do everyone a favor and post the relevant abstract.


don wilkins said at April 10, 2014 2:54 PM:

Before you get too down on psychopaths, you may want to read The Wisdom of Psychopaths by renowned psychologist Professor Kevin Dutton.

spindizzy said at April 10, 2014 3:12 PM:


I agree there is no reason to believe it is being selected out.

Perhaps the advantage it confers is a tendency to have unprotected sex, or not to be in education or work during one's peak reproductive years.

destructure said at April 10, 2014 4:48 PM:


Perhaps. But I wouldn't try to eliminate it from the gene pool until I knew for sure.

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