Monday, 2 April 2012

Intelligence Genetics- Nature versus Nurture

It has been universally accepted that genetics have some bearing on an individual's intelligence, but in modern day science we are still struggling to differentiate between genetic and developed traits. Although scientists continue to unravel the components of our genetic sequence which influence brain function, current research still cannot answer the age-old conundrum of Nature versus Nurture: are we born or made intelligent?

Intelligence is by its nature relatively ambiguous and resists a simple and easy system of measurement. It can be divided into areas of specific interest such as problem solving, rate of learning or memory, yet when trying to get an indication of general intelligence, obtaining reliable quantitative data can be frustrating for a researcher.

A tool commonly used is the IQ (Intelligence Quotient) test, which can give a satisfactory indication of a subject's general mental ability. 

When studying the effects of genetics versus nature, twins that share the same genetic data are useful as any differences in intelligence must be due to differing environments. Preliminary research into the genetics of intelligence consisted of examining the similarities between monozygotic and dizygotic twins' IQ's. Monozygotic twins, those with an identical genome, raised together were seen to have a greater similarity in their general mental ability than dizygotic twins, those with differing genomes. This was a good indicator that genetics had a large part to play in intelligence.

This finding was corroborated by a Dutch study that compared 209 pairs of twins' intelligence using a RAKIT test as they aged through years 5, 7, 10 and 12. Through analyzing genetic trends, percentage values for genetic influence and environmental influence were obtained. The results indicated that genetic factors contributed 26%, 39%, 54% and 64% respectively to intelligence throughout the ages. This steady swing from environmental factors to genetic influences may suggest that although environment may influence basic behavior, our cognitive development and potential is more closely tied to our DNA.

Intelligence in humans has also been linked to certain quantitative traits known to be determined by genetics. Healthy growth of the foetus intrauterine (where itrauterine environment is normal) correlated strongly with higher IQ scores. Additionally, a greater brain volume was seen to increase an individual's intelligence. The volume of grey matter and white matter within the brain, almost entirely heritable traits, were found to relate to speed of processing and memory capabilities.  

However, the specific identification of genes responsible for intelligence is still a relatively vague area of research. Recent evidence may link the catechol-o-methyltransferase gene (COMT), responsible for an enzyme involved in neurotransmitter metabolism, and working memory. Appropriate levels of neurotransmitters (e.g. dopamine and glutamine), are important for normal functioning of the brain, and thus different alleles/activations of this gene may alter cognitive function. However, the COMT gene represents a single patch in the collage of genes which determine intelligence and far more genetic annotation is required before any form of predictive genetics may be employed.

There is still some way to go, but in time the secrets behind genetic intelligence will hopefully be uncovered. Although it would be naive to say that environment does not have an effect on intelligence, new evidence suggests that genetics are a more powerful and determining factor than previously believed.


U.S. National Library of Medicine, 2007, COMT, viewed March 18 2012,

M. Bartel, M.J.H. Rietveld, G.C.M. Van Boal and D.I. Boomsma, 2002, Genetic and Environmental Influences on the Development of Intelligence, Behaviour Genetics, viewed March 16 2012,

Ian J Deary, Frank M Spinath and Timothy C Bates, 2006, Genetics of Intelligence, European Journal of Human Genetics, viewed March 16 2012,

Farnoosh Tayyari, 2004, Genetic Basis of Intelligence, The Science Creative Quarterly, viewed March 16 2012,

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