This study tested genetic influences across emerging cognitive abilities in early infancy, suggesting that a developmental extension of the g factor for cognition is present and may be partly genetically influenced."
Etiological factors were investigated for their influence on variability in different domains of emerging cognitive abilities in early infancy. Genetic and environmental influences were also observed to see how genetic and environmental influences are unique or shared across different domains.
The Mullen Scales of Early Learning (MSEL) was administered to assess development across 5 different scales in a sample of monozygotic and dizygotic twins at 5 months of age. The final sample consisted of 567 infants which is 289 incomplete pairs of same-sex twins.
Twin correlations were higher for monozygotic twins than dizygotic twins on each MSEL scale.
Researchers called the single latent factor that shared variance among different development abilities as infant g which describes an early development extension of the construct g.
The results of the study suggest that the development across different domains is likely influenced by generalized genetic factors.
The fact that a general factor emerges this early (5 months!) is pretty wild. It suggests g isn’t just something that develops from education or culture—there’s a biological foundation present from infancy. The shared genetic variance across motor skills, language, and visual reception supports the idea that general intelligence has deep neurodevelopmental roots. Makes you wonder how much of adult IQ differences are already baked in during the first year of life.
What’s interesting is that they found unique genetic influences on motor and language development on top of the shared “infant g” factor. So it’s not just one big genetic blob—there are domain-specific genetic influences too. This aligns with how adult intelligence works, where you have both general ability (g) and specific abilities. The 54% genetic contribution to shared variance at 5 months is substantial, especially considering these are tiny infants with minimal life experience to shape differences.
It’s fascinating that the MSEL was administered at just five months. That’s a very early point to measure cognitive abilities. Could the researchers clarify which of the five MSEL scales showed the largest genetic influence and which scales were the most highly correlated? Knowing where the infant g factor loads most heavily might tell us more about its nature.
@noah_gowie342 The research abstract explicitly states that they found additional genetic influences specific to early motor and language development. This suggests that while all five scales load onto the general infant g factor, the Gross Motor, Fine Motor, Receptive Language, and Expressive Language scales likely have large genetic contributions that are unique to them, beyond the shared g component.
Why do you treat genetic influences as if they operate independently of environment? Even at 5 months, gene-environment correlations are already in play and as development continues, become increasingly important. Finding genetic influence at 5 months doesn’t mean adult IQ is baked in. It means we’re seeing how genes and environments continuously interact and shape each other over time.
You can’t just extrapolate from infant g at 5 months to adult IQ. The Mullen at this age is heavily weighted toward basic sensorimotor abilities. This is very different from what we mean by intelligence in adults. The factorial structure of cognitive abilities changes dramatically across development. What loads on a general factor in infancy might be basic processing speed or sensorimotor integration, while adult g involves much more complex cognitive processes. So while it’s interesting that a general factor emerges early, we can’t assume it’s the same g or that it predicts adult outcomes strongly.
