The Wilson Effect: the increase in heritability of IQ with age.
Level 5 - mechanism / opinion, no new human data
Narrative review and synthesis of published twin and adoption studies without systematic review methodology.
PubMed 23919982 · doi:10.1017/thg.2013.54
What was done
The authors synthesized evidence from key twin and adoption studies—including studies of twins reared apart across various age groups and settings—to document developmental changes in the genetic and environmental components of intelligence quotient (IQ), proposing the term "The Wilson Effect" for this phenomenon.
What was found
Heritability of IQ increases across development, reaching an asymptote of approximately 0.80 at 18–20 years of age and persisting at that level into adulthood. In parallel, shared environmental influence declines with age, reaching approximately 0.10 by 18–20 years and remaining at that low level through adulthood.
Why it matters
This synthesis formalizes the principle that genetic influences on cognitive ability expand as individuals mature into adulthood, while family-shared environmental influences largely diminish.
Limits
The abstract describes a narrative/diagrammatic synthesis rather than a formal systematic review or quantitative meta-analysis, providing no aggregate sample size or confidence intervals. The conclusions are explicitly derived from and limited to Westernized industrial democracies, precluding direct generalization to other socioeconomic or cultural contexts.
Cited by
- context The heritability of cognitive ability and intelligence test scores increases with age until approximately age 12.