‘Where do you get your brains from?!’ Perhaps your parents have said this to you? I bet even Einstein’s mother or Hawking’s father have thought this about them. Being bright can be a wonderful thing: it can help you triumph in exams and for the truly intellectually gifted, earn you an invitation to mingle with the Mensa elite. But after my mum asked me that very same question, it got me thinking: what exactly makes one person more intelligent than another?
One of the common beliefs is that socio-economic factors influence intelligence: individuals from affluent backgrounds are generally better educated and tend to have jobs that command a high level of brainpower, suggesting intelligence. Advances in genetic studies however, have revealed that what makes one smart is not necessarily how privileged or educated they may be – the secret to intelligence may be determined from birth; imprinted in our genes. The genetic code is made up of nucleotides which provide the blueprint for what makes every human unique. Height, eye colour and skin tone, to name a few, are traits that are governed by our genes. Small changes in the genetic code, known as single nucleotide polymorphisms (SNPs or “snips”) can make some genes more or less active, influencing a number of traits. For example, a hyperactive fat-storing gene may encourage weight-gain. A nucleotide change that restricts melanin production may increase the risk of sunburn. All of these traits are, in part, dictated by our genetic code. Since intelligence is another highly variable trait, can there be genetic variants that decide our intellectual fate?
Scientists have long believed intelligence is heritable and since twins share similar genetic backgrounds, but may have been exposed to different environmental factors, they have commonly been used in studies to help find the genes that shape intelligence. Whilst providing some insight, these studies garnered no tangible answer. Advances in genetic studies however, have allowed the analysis of entire genetic codes (known as genome wide association studies or GWAS) to see if there are any genetic similarities amongst people sharing a common trait (Figure 1).
GWAS have provided some novel insights. One research group in the Netherlands, led by geneticist Danielle Posthuma, published a study comparing the genomes of over 78,000 individuals of European ancestry (Sniekers et al., 2017). Each participant had their genome analysed and were subsequently grouped according to their intelligence, determined by their obtained scores on several IQ and neurocognitive tests. The research uncovered 22 genes containing SNP variations that were shared by the people that had scored highly on the intelligence tests. More recently, the group increased their number of participants and analysed over 250,000 genomes (Savage et al., 2018). In this study, a further 939 new genetic variants were identified. Many of these SNP variants reside in genes that contribute to brain function, memory and neuronal development. More interestingly, some of these genetic variations may possibly protect an individual from suffering with several neurological and psychiatric conditions including Alzheimer’s disease, Schizophrenia and Attention Deficit Hyperactivity Disorder (ADHD).
Both studies have revealed several genetic variations that not only influence intelligence, but also play a role in neurological and psychological behaviours. A further study published by the group in 2018 showed that from nearly 450,000 individuals, 599 of these ‘clever’ genes may increase the risk of developing concurrent anxiety, depression and autistic behaviours (Nagel et al., 2018). This may mean therefore, that being genetically brainier may come at a price.
Advances in scientific technology is making gene therapy – the ability to correct a poorly functioning gene with the correct copy – a realistic future medical intervention. With this in mind, it raises a number of ethical questions: Would you want to tinker with your genetic code to become a revered rocket scientist, or do you graciously accept the genetic cards you were dealt? Would you reconsider being bright if it made you more prone to suffering from depression?
Uncovering the genes that promote intelligence and also those which compromise brain function could prove to be extremely useful: some children are born with intellectual and cognitive disabilities. Mental health is fast becoming a major cause of mortality and morbidity globally, but the biological mechanisms at play that impact on these conditions are not fully understood. If it is demonstrated that particular genetic variations are strongly associated with intelligence or psychological behaviours, they may in fact serve themselves as targets for tailored therapies. Whilst this may be construed as ‘genetic enhancement’, it in fact would improve the quality of life for those living with conditions that would otherwise be inadequately treated.
While the answer to how genes influence intelligence remains unclear, hopefully this blog has given you some ‘intelligent’ insight into the work being done to answer this age-old question. Where did you get your brains from? Well, at least some of it has come from your parents.
Savage, J.E., Jansen, P.R., Stringer, S. et al. (2018) Genome-wide association meta-analysis in 269,867 individuals identifies new genetic and functional links to intelligence. Nat Genet, 50(7): 912-919.
Nagel, M., Jansen, P.R., Stringer, S., et al. (2018) Meta-analysis of genome-wide association studies for neuroticism in 449,484 individuals identifies novel genetic loci and pathways. Nat Genet, 50(7): 920-927.
Sniekers, S., Stringer, S., Watanabe, K. et al. (2017) Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence. Nat Genet, 49(7): 1107-1112.
By Dr. Liam Hurst; Foundation Year 1 Doctor; General Surgery; Norfolk and Norwich Hospital