Certain cognitive skills, such as reading comprehension, math skills, and processing speed, are strongly influenced by genetics, even though they are separate from a person’s overall intelligence. A large-scale new meta-analysis reveals that specific cognitive abilities, like general intelligence, depend on inherited DNA. This distinction opens the door to future genetic profiles that will help guide personalized education. The study was published in the journal Intelligence.
Historically, psychology and behavioral genetics have focused on general cognitive abilities, often referred to as general intelligence. This concept sits at the top of a widely used psychological framework called the Cattell-Horn-Carroll model of intelligence. General intelligence represents the overlapping mental energies or broad processing abilities that help individuals successfully perform a variety of mental tasks. This serves as the underlying engine that improves performance on a variety of mental challenges.
Under this broad umbrella, the model features a middle layer of 16 specific cognitive abilities. These areas of expertise include skills such as quantitative knowledge, reading, writing, short-term memory, visual processing, and processing speed. The lowest layer of the model contains hundreds of individual cognitive tests used in schools and clinical settings. Researchers group these individual tests into intermediate tiers to better understand how a particular domain works.
Past behavioral research has shown that general intelligence is approximately 50% heritable. Heritability is a statistical measure that describes how much variation in a particular trait within a population is due to heritable genetic differences. This does not mean that an individual’s intelligence is strictly half genetic and half environmental. Instead, it describes the differences that unite people within a particular group.
Family and adoption research shows surprising developmental trends in general intelligence. In fact, the heritability of general intelligence increases as people get older. It rises from about 20 percent in infancy to 40 percent in childhood and finally reaches 60 percent in adulthood. People appear to grow in line with their genetic predispositions as they gain the independence to choose an environment that matches their innate abilities.
Far fewer data are available regarding the genetics of the intermediate tier of specific cognitive abilities. King’s College London researcher Francesca Procopio and her colleagues wanted to understand whether these special abilities are inherited in the same way as general intelligence. They also wanted to know whether certain abilities are more influenced by genetics than others. Early reviews in the 1970s and 1980s suggested similar genetic roots, but those early studies relied on very small sample sizes.
The main focus of their modern research was whether genetic influences on specific cognitive abilities are simply a byproduct of general intelligence. People with higher general intelligence tend to perform better on certain tests, creating overlapping statistical effects. The researchers wanted to isolate certain abilities to see if they had their own distinct genetic underpinnings. If we could separate specific skills from general intelligence, we could plan our own cognitive profile.
To answer these questions, Procopio and her team conducted a meta-analysis that combined data from 77 previous publications. They focused on twin studies, a classic and reliable method in behavioral genetics. By comparing identical twins, who share 100% of their genes, to dizygotic twins, who share about half of their genes, researchers can estimate the genetic contribution to a particular trait. The extra similarities observed in identical twins are likely due to shared DNA.
The authors compiled 747,567 twin comparisons across 11 of 16 specific cognitive domains within the broader theoretical model. They mapped the many different tests used in the original study onto these broad categories to create a unified framework. This aggregation allowed us to calculate average heritability estimates for specific abilities and compare them across different age groups. The final dataset provided sufficient statistical power to detect small differences between cognitive domains.
The combined results showed that the average heritability of all specific cognitive abilities was 56%. This number is slightly higher than the average heritability of overall general intelligence. However, the exact level of genetic influence varied widely between different specific domains. Some areas of cognition appear to be much more dependent on genetic differences than others.
Quantitative knowledge, reading, writing, and processing speed were the most heritable traits, with estimates of more than 60%. In contrast, fluid reasoning and short-term memory declined by nearly 40%. Fluid reasoning involves the ability to solve novel problems and is considered a core element of general intelligence. This particular contrast presented an unexpected puzzle for the research team.
Many psychologists believe that the acquired knowledge domain depends primarily on school instruction and shared childhood experiences. The data showed that these learned themes were more strongly tied to genetics than innate fluid reasoning. This finding challenges the assumption that subjects taught in schools represent purely environmental outcomes rather than innate biological abilities. This suggests that individuals have a strong genetic predisposition to acquiring certain types of academic knowledge.
The team also noticed surprising differences within functionally similar categories. Processing speed, the ability to perform simple cognitive tasks automatically under focused attention, was 64% heritable. On the other hand, reaction and decision-making speed, which performs basic responses to simple stimuli, had one of the lowest heritability estimates at 42%. The authors propose that tasks that require higher levels of mental complexity may simply capture more genetic influences.
Meta-analyses then assessed developmental patterns and revealed different aging trajectories for specific abilities compared to general intelligence. Genetic influences on general intelligence are expected to increase from childhood to adulthood as individuals select their own intellectual environments. Certain cognitive abilities do not show this same upward trend over the lifespan. Instead, they follow a flatter trajectory after their initial childhood bumps.
The heritability of certain abilities increases from infancy to middle childhood and then declines or stagnates slightly. For example, the heritability of reading and writing showed a general trend of decreasing influence after middle childhood. Researchers suggest that the apparent increase in heritability during childhood may be artificially inflated because of the difficulty in testing young children reliably. Some researchers suspect that universal education would reduce environmental disparities and stabilize the genetic predispositions of these subjects during school age.
When the researchers mathematically adjusted the data to remove the influence of general intelligence, they found another unexpected result. Isolated specific cognitive abilities remained highly heritable, with an average of 53%. This means that the genetic basis of skills such as mathematics and spatial reasoning is largely completely independent. It is different from the genes that drive a person’s overall intellectual ability.
This study includes several limitations based on available historical data. Five of the 16 specific cognitive categories were completely missing twin comparisons, meaning that certain areas such as motor skills or olfactory abilities could not be analyzed. Moreover, only two cognitive categories had enough data to be tracked over the human lifespan. This continued lack of data makes it difficult to draw absolute conclusions about cognitive aging.
Dividing the data into different age groups naturally reduces the statistical power of developmental analyses. The researchers also noted that studies conducted in different years and countries often used different exact testing methods, adding noise to the combined data. Organizing diverse cognitive tests into broad categories necessarily requires subjective classification. Paper-and-pencil tests are not completely reliable, so the mathematical methods used to distinguish between general intelligence and specific abilities are also approximations.
In the future, the research team hopes that these findings will encourage more detailed genetic studies using modern DNA sampling. They hope to identify the precise genetic variations associated with specific abilities to build a customized cognitive profile. Identifying these sequences may eventually allow scientists to predict an individual’s cognitive strengths and weaknesses from an early age. This knowledge serves as an additional tool for educators and parents.
Understanding these profiles independently of general intelligence may one day allow educators to tailor early intervention. Rather than waiting for students to struggle in a particular subject, teachers can anticipate learning hurdles and adjust their teaching methods. Nurturing a child’s natural strengths while minimizing his or her weaknesses will help maximize a child’s educational potential. Ultimately, this study shifts the focus from a single intelligence score to the diverse context of individual abilities.
The study, “Genetics of Specific Cognitive Abilities,” was authored by Francesca Procopio, Quan Zhou, Ziye Wang, Agnieska Gidziela, Kailirimfeld, Margherita Malanchini, and Robert Plomin.
