Cognitive tests in infancy are key to predicting intelligence in adulthood

Modern science is increasingly turning to the question of how early stages of human development determine future mental abilities. A recent large-scale study demonstrates that cognitive tests conducted in infancy can serve as a reliable indicator of intelligence at age 30 and beyond.

The study involved more than 1,000 twins, allowing the researchers to examine not only the influence of genetics but also the role of environment. The analysis began in 1985, when Colorado twins were first assessed at 7 months of age on seven measures of cognitive ability, including vocalization, performance on simple tasks, and novelty preference — the tendency to play with new toys over familiar ones.

Over the next decades, the researchers regularly collected developmental data on the participants, conducted lab tests, made home visits, conducted interviews, and observed the children’s behavior. They found that measures taken in infancy could predict about 13 percent of the variance in cognitive ability in adults at age 30. Novelty preference and task orientation were particularly strong predictors.

One of the key aspects of the study was comparing the influence of genetics and the environment. To do this, the scientists used a classic method - they compared the indicators of identical and fraternal twins. Since identical twins have 100 percent of their genes in common, and fraternal twins - about 50 percent, the difference in their cognitive tests allows us to estimate the contribution of heredity.

The results showed that genes play a significant role: genetic factors measured at 7 months explain about half of the variance in cognitive ability at age 30. But crucially, the influence of the environment also remains significant. About 10 percent of the variance in adult cognitive ability is explained by factors related to early childhood conditions, and this effect persists even after accounting for genetic predisposition.

Interestingly, with age, the influence of the environment gradually decreases, giving way to genetic factors. However, even in adulthood, according to scientists, the role of constant cognitive training, educational programs and a healthy lifestyle is important for maintaining mental activity.

Study author Daniel Gustafson emphasizes that the findings support the importance of early childhood as a critical period for the development of cognitive abilities.

“Our findings show that even in the first years of life, processes occur that have long-term effects on a person’s cognitive abilities,” Gustafson says. He adds that creating favorable conditions during this period is an investment in the future that can reduce the risk of developing age-related cognitive impairments such as dementia.

Age-related disease specialist Chandra Reynolds said understanding how cognitive abilities are formed is important not only for education and professional practice, but also for preventing age-related brain diseases.

"If we can identify what factors contribute to high intelligence and cognitive resilience, we can develop strategies to enhance them," she said.

While there is no single gene for intelligence, combining multiple genetic variants provides insight into how heredity influences brain development, Gustafson says. He adds that the results show a strong match between genetic predictions and actual test results in adult twins, confirming the method's reliability.