Is Intelligence Heritable?

Throughout the course of modern science, a popular topic of research and discussion has been whether intelligence is heritable. Twin studies have suggested a genetic influence on mathematical abilities, but when considered, environmental factors may also have played a part in the development of the individuals’ intelligence (Pinel, 1). Therefore, the argument remains between nature and nurture: which one contributes to an individual’s general intelligence and cognitive ability? Are some people just born smarter than others, or does everyone, notwithstanding mental disabilities, have the equal opportunity to garner intelligence? The research of various studies so far concludes that both are true; while intelligence is rooted in genetic influence, environmental factors play a crucial role in the extent of that influence.
In a study published in 2009 in the Journal of Neuroscience, researchers used a new type of brain-imaging scanner in a twin study to show that intelligence is strongly influenced by the quality of the brain’s axons, which send signals throughout the brain. The faster the signaling, the faster the brain processes information, and since genes influence the integrity of the axons, these genes indirectly play a role in an individual’s intelligence. The study proposes that genes appear to influence intelligence by determining how well nerve axons are sheathed in myelin. The correlation to individual intelligence is based on the connection that the faster the myelin, the faster the nerve impulses, and therefore the faster capability for the brain to process information. The researchers scanned the brains of 23 sets of identical twins and 23 sets of fraternal twins. Using the fact that identical twins share the same genes,...

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...enes and general intelligence. The results only exhibited one nominally significant association, which is less than what would be expected by chance alone. The study then followed the methods of the 2011 study, and in applying the same procedure in its analysis, estimated that the 630,000 SNPs in the data jointly accounted for forty seven percent of the variance in general intelligence. The combined results of this study further reinforce the view that intelligence is a highly polygenic trait.
A more recent study published in 2013 in NeuroImage also worked on the basis of the past twin studies which have long suggested a genetic influence between specific candidate genes and intelligence. This study examined the heritability of the trait by jointly estimating genetic and environmental contributions with a modified model which was classically used in twin studies.