October 16, 2007
Twin Brain Scan Studies Find Genetic Influences On Intelligence

Evidence suggests that lots of genetic variations that influence intelligence are waiting to be found.

Evidence is accumulating that brain structure is under considerable genetic influence [Peper et al., 2007]. Puberty, the transitional phase from childhood into adulthood, involves changes in brain morphology that may be essential to optimal adult functioning. Around the onset of puberty gray matter volume starts to decrease, while white matter volume is still increasing [Giedd et al., 1999].

Recent findings have shown, that variation in total gray and white matter volume of the adult human brain is primarily (70–90%) genetically determined [Baare et al, 2001] and in a recent magnetic resonance imaging (MRI) brain study with 45 monozygotic and 61 dizygotic 9-year-old twin-pairs, and their 87 full siblings also high heritabilities have been found [Peper et al, in preparation]. Thus, while environmental influences may play a role in later stages during puberty, around the onset of puberty brain volumes are already highly heritable.

The more genes are found that influence intelligence the greater will be the desire of future parents to use reproductive technologies to make little Jill and Johnnie smarter. Reports like this one indicate that we are coming up on a mad scramble to use offspring genetic engineering technologies. Us older people will be dumb compared to the average child born 50 years from now. If you are smart then are you prepared to find yourself in the left hand side of the intelligence distribution? Or do you plan to use cybernetic implants to keep up with the younger generations?

These researchers compared the volumes of a large number of areas of the brain between twins while also testing them for intelligence. They found genetic influences on the brain density of many areas of the brain as well as genetic influences on intelligence.

Although genetic effects on morphology of specific gray matter areas in the brain have been studied, the heritability of focal white matter was unknown until recently. Similarly, it was unresolved whether there is a common genetic origin of focal gray matter and white matter structures with intelligence. In our study involving 54 monozygotic and 58 dizygotic twin pairs and their 34 singleton siblings, verbal, and performal intelligence were found to share a common genetic origin with an anatomical neural network involving the frontal, occipital, and parahippocampal gray matter and connecting white matter of the superior occipitofrontal fascicle, and the corpus callosum [Hulshoff Pol et al., 2006]. For the genetic analyses, structural equation modeling and voxel-based morphometry were used. To explore the common genetic origin of focal gray matter and white matter areas with intelligence, cross-trait/cross-twin correlations were obtained in which the focal gray matter and white matter densities of each twin are correlated with the psychometric intelligence quotient of his/her cotwin.

The results of this study indicate that genes significantly influence white matter density of the superior occipitofrontal fascicle, corpus callosum, optic radiation, and corticospinal tract, as well as gray matter density of the medial frontal, superior frontal, superior temporal, occipital, postcentral, posterior cingulate, and parahippocampal cortices. Moreover, the results show that intelligence shares a common genetic origin with superior occipitofrontal, callosal, and left optical radiation white matter and frontal, occipital, and parahippocampal gray matter (phenotypic correlations up to 0.35).

These researchers aren't doing DNA sequencing because DNA sequencing still costs too much. But with costs of DNA sequencing and DNA testing rapidly falling brain researchers are going to be able to do massive genetic comparisons in 5 to 10 years that will give them a large enough quantity of genetic information to be able to run down and identify the genetic variations that cause differences in brain density, brain volume, and intelligence. Brain scans on much larger sets of twins combined with full genetic sequencing on those same twins will answer many of the questions we have about genetics and intelligence.

Share |      Randall Parker, 2007 October 16 05:35 PM  Brain Intelligence

HellKaiserRyo said at October 16, 2007 6:10 PM:

If you are smart then are you prepared to find yourself in the left hand side of the intelligence distribution? Or do you plan to use cybernetic implants to keep up with the younger generations?

Who doesn't plan to use cybernetic implants... Cybernetic implants will eliminate all the misery caused by low intelligence. Maybe getting cybernetic implants would be a REQUIREMENT for obtaining welfare. In that case, those who receive it could be reeducated at an excellent school and eventually find a fulfulling career (i.e. a non-menial job) and obviate the need for welfate.

It would also drastically reduce crime if a state-sponsored enhancement program is used for universal access:

"What do you see as the principal social problems caused
by low intelligence levels?

Poor educational attainment, poor vocational skills, high unemployment,
high rates of crime and single motherhood. Low
intelligence is a major causal factor in all these social pathologies.

And how serious are these problems?

They are very serious. All these problems have been identified
for some time in the United States and have been well reviewed by
Richard Herrnstein and Charles Murray in The Bell Curve. They
have also appeared in Britain. For instance, official government
figures have shown that in 1995 62 per cent of young black males
are unemployed, as compared with about 18 per cent of whites.
Black crime in Britain is about three times higher than white. The
1991 census showed that slngle motherhood among blacks was
51 per cent, about double that of whites.

Why should lower intelligence cause more crime?

Most crimes are committed by people with low intelligence.
This is partly because the unintelligent have less to lose by being
caught because they generally have poor jobs, or are unemployed,
and partly because they can’t figure out so well the likelihood and
consequences of being caught."


I want to use them cure myself of the malady known as "Homo sapiens".

How come you never mention state-sponsored eugenics Randall? It could solve many problems if it is combined, not with selective breeding, but assiduous molecular manipulation!!!

Randall Parker said at October 16, 2007 10:39 PM:


I think I've written about state-sponsored eugenics. But I guess it has been a while. I'll look for reasons to bring it up in future posts.

Keep in mind that there are many governments. They do not share common goals and values. So different eugenic breeding programs will pursue different goals. Future generations could be biologically more different between countries than they already are now. Granted, IQ gaps might close. But values gaps due to different neural wiring could become even greater.

Of course, these same sorts of divergences will happen if individuals control genetic choices for offspring. Though individuals will make different choices than governments.

Solve problems: dummies will become less common. But other problems might become more common.

HellKaiserRyo said at October 17, 2007 1:06 AM:

I meant a program where the state would pay for eugenic enhancement such as genetic engineering without coercion as it would be up to the parents to take advantage of such a provision. One can go to Linda Gottfredson's page and find studies that show correlations between IQ and productivity, so in the long run such a program would be an economic boon. It is not a waste of money akin to sponsoring things such as breast enhancements and plastic surgery (with the exception regarding certain accidents) as those do not contribute to health or productivity.

Of course, you are indeed correct that:

"Keep in mind that there are many governments. They do not share common goals and values. So different eugenic breeding programs will pursue different goals. Future generations could be biologically more different between countries than they already are now. Granted, IQ gaps might close. But values gaps due to different neural wiring could become even greater."

Differences within individuals and families would also contribute too. For example, I do not know if Catholics would embrace genetic engineering. Their Luddite tendencies say no, but the allure of conceiving a child which would be impervious to academic failure (in today’s system) is quite tempting. In Eugenics, Lynn does consider differences in government public policy, and he concludes that China will supersede the United States as world power due to an authoritarian state eugenics program (embryo selection would be used initially). Lynn also acknowledges that eugenics would be used in the Western democracies, but in a free market fashion. Lynn, unfortunately, doesn't consider a subsidized program that would pay to allow parents to enhance their children in certain ways. Of course, it wouldn't pay for ALL enhancements, just those that significantly contribute to inequality and health. Positional enhancements, such as height, "athleticism," sex, pulchritude, I would image, would not be sponsored.

Contributing to the decline of the West in Lynn's vision is not some malevolent AI or grey goo, but a racial balkanization. It is also mentioned in the link I have provided. I do not know if such an event will happen, but if it is possible, a panacea such as powerful nootropics would easily avert it. Too bad Merck, BMS, Pfizer, etc. has no known R&D program for those noble cause.

Regarding the two options of free-market eugenics and authoritarian eugenics, in my opinion, the LATTER seems to be a lesser evil. At least it wouldn't significantly contribute to inequality if EVERYONE was coercively enhanced. It is better than having the technology restricted to those who couldn't pay for it. Of course, the latter would defeat the purpose of authoritarianism; people with high IQs (a solecism in such a state because everyone would be smarter) make poor serfs and wouldn't tolerate elitism.

As for future problems regarding individual choice, maybe genetic engineering will exacerbate some of the problems of human nature:

I will quote my favorite bioethicist, James Hughes.

"Another theorist who argues that egalitarians should embrace subsidized germinal choice technology, including enhancement, is the Princeton University Bioethicist Peter Singer. In Singer's 2001 A Darwin Left: Politics, Evolution, and Cooperation, he argues that the Left has ignored and denied the sociobiological constraints on politics to its own detriment. Singer contends that there is a biologically rooted tendency towards selfishness and hierarchy in human nature that undermines egalitarian social reforms. If ambitious egalitarian programs of social reform and democratic cooperation are to succeed, Singer argues, we must employ the new genetic and neurological sciences to identify and modify the aspects of human nature that cause conflict and competition. "In a more distant future we can still barely glimpse, it may turn out to be a prerequisite for a new kind of freedom: the freedom to shape our genes, we can build the kind of society we judge best." Toward that end Singer advocates a program of voluntary, socially subsidized genetic enhancement.”

“Society could forbid the most powerful enhancements to those who refused to be screened for basic empathy and morality, just like we do for a handgun purchase. The manufacturers of cognitive enhancement software could be obliged to include empathy and moral decision-making supports as a feature just as we require warnings and child-proof caps on medicine and air bags in cars”

Should we manipulate human nature? Would this be mind control and slavery? Would it create an obsequious and biddable race?

A talk by Hughes called “Virtue Engineering” argues that we should use technology to help us become better people and control our desires. It also mentions that racism has a genetic etiology at around 11:45. Returning to your original point, “racism” might be augmented in the children of white nationalists and other such people. Would state intervention become detrimental coercion and detrimentally eliminate diversity?


Kelly Parks said at October 17, 2007 9:04 PM:

Not to wax poetic or anything, but this is one possible path to the singularity. One of the many things smarter people will be able to do is figure out how to make people even smarter, which in turn allows...well, you get the idea. Very quickly you get people who are doing science we wouldn't be capable of understanding no matter how slowly they explained it to us, just as we could never explain quantum mechanics to someone so profoundly retarded that they can't tie their own shoes.

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