Nature vs Nurture: Does Your DNA Determine Your Intelligence?

Are you extremely, exceedingly smart? Do you regularly use words like ‘pejorative’ and ‘antidisestablishmentarianism’? Do you write a monthly science feature for The Adelaide Review and generally feel pretty bloody chuffed with yourself?

If you have answered ‘yes’ to any of these questions, you have probably already spent some time considering the source of your intellect. You probably already know then, that the general consensus is that intelligence is influenced by some combination of both nature — that is, heredity — and nurture — that is, environment. What remains less clear though, is which genes are responsible for intelligence, and to what extent.

First, if you can bear it, come with me on a journey back to high school science class where you would surely have learnt about the structure of deoxyribonucleic acid, or DNA.

DNA is in most cells of the body, and is typically organised into 23 pairs of chromosomes, with one from each pair inherited from each parent. DNA is made up of nucleotides, which contain a phosphate, a sugar, and a nitrogen base; cytosine (C), thymine (T), adenine (A), and guanine (G). Different sequences of nitrogen bases carry different biological messages, and these messages make up your genome, which determines all the proteins you will ever synthesise.

These proteins control the structure and function of all cells. Nucleotides found in particular chromosomal regions are called SNPs (single nucleotide polymorphisms). The sequence of nucleotides on a particular SNP (pronounced ‘snip’) is the most common source of genetic variation between people. The best way to study whether variations in SNPs are associated with certain diseases or traits is via genome-wide association studies (GWAS). So far, GWAS have also been used to identify SNPs associated with Crohn’s disease, Parkinson’s disease, and diabetes.

A recent GWAS published in Nature Genetics involved the sequencing of DNA from more than 78,000 people, an unprecedented sample size for studying the genetic basis of intelligence. The aim was to find a relationship between certain SNPs and performance on an IQ test, as an indicator of performance. Of the 12,000,000-plus SNPS that were analysed, relationships were identified between IQ test performance and 336 particular SNP variations, implicating a total of 22 genes, and explaining 5 per cent of variation in test performance. Half of these genes were not previously known to be related to intelligence. Using a different technique that involved sequencing larger patterns of SNPs, the researchers identified a further 29 genes associated with intelligence that were previously unknown. While it may seem like GWAs take an astounding volume of data, and whittle it down into a seemingly trifling outcome, previous studies of the genetic basis of intelligence have been able to explain only 2.5 per cent of the variance between individuals. Pffft! Amateurs.

The researchers conducted their own quality control check on their findings, by checking for a relationship between each of the 336 SNPs and level of education in a new sample of 200,000 people. There was an almost perfect relationship between the ‘intelligence’ SNPs and level of education. This means that the presence of certain genes is also associated with level of education, another indicator of intelligence. Trifling numbers or not, these data provide new knowledge about which genetic variations are likely to lead to increased intelligence, and indicate that intelligence and learning may be governed by some of the same genetic processes.

Good news for some. The flipside of course, is that individuals without these particular SNPs may be more likely to struggle intellectually and may find it more difficult to learn.

So how do we use these kinds of genetic insights for good instead of evil? One potential outcome is the early identification of children at risk for learning problems or intellectual deficits, and the ability to develop and implement environmental interventions to counteract these issues.

Indeed, studies of identical twins raised separately from birth have shown that those raised in intellectually ‘rich’ environments have significantly higher IQ scores than their genetically identical counterparts. And, keep in mind that intelligence is also influenced by a number of non-genetic causes, like being read to more, or having only the most up-to-date Apple products, or getting one of those tiny Hot Wheels laptops for Christmas. So, if you’re a supernerd about to have a kid: don’t rest on your genetic laurels.

Dr Jessica L Paterson, Senior Research Fellow, CQUniversity, Appleton Institute