Dec 22 2015

The Genetics of Intelligence

DNA1A new study published in Nature Neuroscience explores genes that correlate with intelligence in healthy individuals as well as those with epilepsy and cognitive disorders. They looked at the brains of patients undergoing surgery for epilepsy, which means that a sample of their brain tissue was available. This allowed them to find which genes were highly expressed in brain tissue.

They then combined this data with other data sets including genetic analysis and IQ testing on healthy individuals and those with developmental disorders. They analysed thousands of genes to find those that correlate with differences in IQ.

They found that there are two sets of genes, which they are calling M1 and M3, that highly correlate with intelligence. M3 contains 150 genes that are tightly developmentally regulated. Keep in mind these are genes that they know are highly expressed in the brain.

What this means exactly is not yet known, but there are some obvious hypotheses. The researchers believe that these two gene networks are each regulated in a coordinated way and direct brain development. A certain set of gene variants is associated with optimal brain development and therefore function. The more variants differ from this optimal arrangement, the lower IQ, and not only for the range of healthy individuals, but the same genes seem to be involved in at least some individuals with cognitive impairment and epilepsy.

As an aside, epilepsy is often (not always) a marker for disorders of brain development. Do not think of this as people with epilepsy have low IQ. Rather, people who have severe disorders of brain development tend to have epilepsy.

The researchers further speculate that there may be master control genes that coordinate the functioning of the M1 and M3 sets of genes. This is not yet known, but is likely given what we know about gene regulation.

The next steps will including finding the master control mechanisms for these gene sets. Also, researchers would like to discover what these genes do, exactly. What proteins do they code for, and what brain developmental pathways do they influence?

Of course, science news stories must contain a section in which the practical applications of the new discovery are discussed. It is an obvious question and is often interesting, but I do think this speculation often gets more attention than it deserves, and sometimes goes wildly beyond the evidence. In reality we can’t always predict how basic science knowledge will pay off in the future. The knowledge is important unto itself.

News reports on this story have mentioned two possible applications. The first is that these genes could be tweaked in order to make people more intelligent. With the rapid progress of CRISPR technology, this is becoming more feasible. We are a long way from this type of application, and it is not known if altering these genes in an adult will have any effect or if they have to be changed in the embryo. Both situations are plausible, in the former case if genes affect neuronal functioning and not just their development.

Another study earlier this year examining standardized exam scores and genes from 12,500 twins found that between 54 and 65 percent of differences in the exams could be explained by genetic differences. This is always tricky data, and the very concept of using this type of twin analysis is not universally accepted, but it does suggest a strong contribution to overall intelligence from genes.

Genetics, however, are not destiny, as many are quick to point out. This still leaves a large portion that is down to environment, and that is the component we can most readily affect (at least for now).

The other possible application, as reported by the Telegraph, is this:

Report author Professor Robert Plomin believes that children should be genetically screened at the age of four so that an individualised curriculum could be tailored to their needs.

“Understanding the specific genetic and environmental factors influencing individual differences in educational achievement – and the complex interplay between them – could help educationalists develop effective personalised learning programmes, to help every child reach their potential by the end of compulsory education,” he said.

I found that suggestion a bit surprising. It certainly raises fascist images of GATACCA, even though the intention is completely benign. That aside, I don’t find the suggestion very compelling.

First, while genetics may predict a portion of overall intelligence, specific genetic variants, because they do interact with each other and the environment (and probably epigenetic factors), may never have sufficient predictive value to offer sufficient insight into a specific individual. It may be that genetic information is never as useful as regular aptitude testing.

Second, I am not convinced that personalized learning programs are of any value. The evidence does not support the conclusion that children have their own learning style, and that catering to that style is of any advantage.

Again, if you want to individualize a program you are probably better off using direct testing of academic ability and potential, and ongoing assessment of how each student is doing. Individualized attention and going at a rate that is appropriate for each student is advantageous (if resource intensive), and I don’t see how genetic information will help with this.

Using genes as a dominant determining factor in education may in fact be detrimental. It will punish students and their parents who provided an excellent learning environment, so that their children will have made good use of their potential. They will be judged not for their hard work but for their bad genes.

In any case – it just seems much better to use actual ability rather than using genes as a marker for potential ability. The latter approach does treat genes as destiny, which we know is not the case.


The new study provides insight into the genetics of brain development and function, which of course is tied to overall intelligence. It is interesting that the correlations found hold up not just for the spectrum of healthy individuals, but for those with developmental disorders and cognitive impairment.

This type of information is interesting enough on its own, but it is made more provocative as we are apparently on the cusp of the gene modification revolution. It does seem likely that we will face a not-so-distant future in which we will have to decide on the ethics of tweaking human genes to create more intelligent children (not necessarily super-intelligent, but at least at the upper end of current human variation).

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