Intelligence has strong genetic basis: study

Is intelligence determined by genes or by the environment? This is one of the most important debates in Psychology. A study by a team of scientists at the University of California, Los Angeles (UCLA) has led credence to the theory that intelligence has a strong genetic basis.

In the study, the researchers assessed white matter integrity using diffusion MRI in 92 identical and fraternal twins (Identical twins have the same genes while fraternal twins share only half their genes) and compared it with Intelligence Quotient (IQ) scores.

White matter is one of the three main components of the brain, the other two being grey matter (largely containing nerve cells) and Substantia Nigra. White matter largely consists of bundles of axons which interconnect grey matter parts and transmit impulses between nerve cells.

White matter integrity refers to the quality of the axons in white matter. Better quality axons transmit impulses faster. Better the white matter integrity, higher the intelligence.

The researchers found clear differences between identical and fraternal twins in the correlation of their white matter integrity with their IQ scores.

“White matter integrity (FA) was under strong genetic control and was highly heritable... common genetic factors mediated the correlation between IQ and white matter integrity, suggesting a common physiological mechanism for both, and common genetic determination,” said the results of the study, published in the Journal of Neuroscience.

In other words, white matter integrity is largely determined by genes, which suggests that the information processing capacity of humans, that owes heavily to genetic factors.

“The study is the first to analyze genetic and environmental factors that affect brain fiber architecture and its genetic linkage with cognitive function,” the report says.