IQ- nature or nurture?

As an aspiring medical student, I am preparing to take the UKCAT exam this summer. Whilst practising a mock paper my immediate thought was that it is similar to an IQ test. This intrigued me and lead me to question the nature of IQ and, more specifically, if it is derived from genetics or environmental factors.

IQ, which stands for Intelligence Quotient, is a method of measuring the abstract nature of intelligence. It aims to score an individual on their general cognitive ability, or the general factor of intelligence written as “g”, from a series of standardised tests. These scores are also closely correlated with other aspects of life such as health, happiness, choice of romantic partner and longevity.  This is because the same variant of a gene can have a positive effect on intelligence, but a negative effect on a different trait, for example seven genes for intelligence are also associated by a negative correlation with schizophrenia.

The ‘Twins Early Development Study’, conducted by Richard Plomin, investigated the cognitive abilities of nearly 15,000 pairs of British twins (both monozygotic and dizygotic) at the ages of 2, 3, 4, 7, 9, 10, 12, 14, 16, 18 and 21 in order to gain understanding of the relationship between IQ and genes. The aggregation of single-nucleotide polymorphisms (DNA sequence variations often referred to as SNPs) in genome wide association studies concluded that inherited differences in SNPs accounts for approximately 50% of an individual’s intelligence. Each SNP has very little effect on IQ, only increasing or decreasing IQ by an average of 0.005%, and so 10,000 of them must be aggregated to equal the 50%. Genome Wide association studies can be used similarly to link gene variants with around 2,000 other traits including likeliness to have heart failure, depression and diabetes. 

A year ago, no specific gene had been associated with performance on an IQ test, however since then an experiment directed by Danielle Posthuma in Amsterdam has caused a major advancement in understanding the genetic underpinnings of intelligence. The study began in May 2017 by comparing the genotypes of 78,308 people with their IQ scores to successfully establish links with variants of 22 genes. By March 199,000 peoples’ genotypes had been investigated to identify links with over 500 genes variants.

From this research, Plomin proceeded to explain the potential to generate genetic IQ scores of infants to predict their future academic potential, and even set them into groups of similar ability, changing the education system massively.  However, this is unlikely and very controversial as the IQ predictions so far have not been very precise with Plomin himself coming across many twins who have performed both much better and worse than expected. Posthuma states how unlikely it is realistically because “We will never be able to look into someone’s DNA and say your IQ will be 120.”.

In conclusion, IQ is affected equally by genetics and environmental factors. Calculating the likeliness of developing traits, such as a high or low IQ, from gene variants is momentarily too inaccurate to act on but is an exciting prospect to investigate further in the future.




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