Your Baby’s Favorite Toy Could Hint at Their Future IQ

A study involving more than 1,000 twins suggests that the environment during very early life plays a more important role than previously believed.

Watching a baby babble, play, and interact with others can offer valuable clues about their cognitive abilities later in life, according to new research from the University of Colorado Boulder published in the journal PNAS.

The study, which examined more than 1,000 twins, found that tests conducted as early as 7 months old can help predict performance on cognitive assessments at age 30. It also revealed that an infant’s environment has a greater impact on lifelong cognitive development than previously understood. According to the authors, early-life conditions could even influence the risk of developing dementia in later years.

“Our findings highlight the enduring consequences of the very early childhood environment on cognitive ability and suggest that early life is a critical developmental period that we should be paying attention to,” said lead author Daniel Gustavson, assistant research professor at the Institute for Behavioral Genetics (IBG).

What twins can teach us

Similar to “IQ,” general cognitive ability (GCA) is a single, combined measure of a person’s ability to learn, reason, understand, and solve problems.

Previous studies have shown that much of a person’s GCA is established by childhood. An 8-year-old’s score on a series of cognitive tests will closely resemble their score at age 30. Intelligence measures at age 20 are strongly correlated with those at age 62, and IQ tends to remain stable from age 11 through age 90.

However, few researchers have looked further back to investigate whether any signs in infancy can predict cognitive performance in adulthood and old age.

In this study, lead author Daniel Gustavson and senior author Chandra Reynolds, a professor of psychology and neuroscience, examined data from 1,098 participants in the Colorado Longitudinal Twin Study. The Institute for Behavioral Genetics (IBG) launched the study in 1985, enrolling infant twins from Colorado’s Front Range to explore how genetics and environment influence different aspects of development.

Since then, researchers have collected extensive data through regular lab visits, home assessments, surveys, interviews, and behavioral tests.

“We have co-authors on this paper who have been involved since the start and watched these twins grow up,” said Gustavson.

As early as 7 months old, researchers assessed seven measures of cognition, including vocalization, ability to stay on task, and “novelty preference” — whether the infants preferred to play with new toys over ones they were familiar with.

Age-appropriate cognitive assessments have been done at five points, so far. The team found that looking at cognitive tests in infancy could predict about 13% of the variance in scores at age 30. Two measures —novelty preference and task orientation—were the strongest predictors. This early life “signal” is not huge, the authors note.

“We certainly do not want to imply that cognition is somehow fixed by seven months old,” Gustavson said. “But the idea that a very simple test in infancy can help predict the results of a very complicated cognitive test taken 30 years later is exciting.”

Nature, nurture or both?

To explore what role genetics vs. environment plays, the study compared GCA score differences between identical twins, who share 100% of their genes, and fraternal twins, who only share half of their genes. In general, if there is greater similarity among identical twins than fraternal twins, this suggests that genes play a strong role in that trait.

They also analyzed the twins’ DNA collected via blood or saliva.

As expected, genes played a big role in influencing general cognitive ability, with genetic influences measured by age 7 accounting for about half of the variation in scores at age 30. But environment also had a significant and lasting impact.

“One of the most exciting findings was that 10% of the variability in adult cognitive ability was explained by environmental influences before year one or two,” said Gustavson.

The older the children got, the more influence genes had and the less environment had. “This suggests that even the pre-preschool environment matters,” Gustavson said.

Reynolds, who studies age-related diseases including Alzheimer’s and dementia, says the findings could have implications not only for how youth do in school or how adults perform at work but also how prone they may be to age-related cognitive decline.

“Cognitive aging is a life-long process, not just something that begins in mid-life,” she said. “It could be that certain interventions, like strong educational foundations in early life could help maximize what people are capable of and help them keep that cognitive gas in the tank for as long as possible.”

A polygenic score for intelligence

The study also confirms that “polygenic scores” can be a useful tool.

Polygenic scores are single numbers that aggregate a person’s genetic variants to estimate predisposition to a trait, like intelligence.

“There are thousands of genes that influence intelligence, so you are never going to find an ‘intelligence gene’, but we have found many with tiny effects that when put together can have an impact,” Gustavson said.

For the study, the researchers used genetic data from nearly 1 million individuals gathered via large datasets like 23 and Me to give each of the adult twins a polygenic score based on their own DNA, for cognitive ability.

Remarkably, the twins’ scores closely matched what would be expected based on their tests when they were babies.

“Studies like ours show us that both family-based and genomic-based datasets are valuable in answering questions about how genetic and environmental influences change across the lifespan,” said Gustavson.

Reference: “Stability of general cognitive ability from infancy to adulthood: A combined twin and genomic investigation” by Daniel E. Gustavson, Giulia A. Borriello, Mohini A. Karhadkar, Soo Hyun Rhee, Robin P. Corley, Sally-Ann Rhea, Lisabeth F. DiLalla, Sally J. Wadsworth, Naomi P. Friedman and Chandra A. Reynolds, 19 May 2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2426531122

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