Expert Commentary

The nature and nurture of high IQ: An extended sensitive period for intellectual development

2013 study from Pennsylvania State University and other institutions published in Psychological Science on the interplay of nature and nurture in IQ development.

As parents have long observed, children learn with ease, rapidly absorbing information in their environment and picking up new skills and knowledge at a rapid pace. Things are not so easy for most adults — in particular, they have more difficulty learning languages — but they can be masterful at relying on hard-won experience to get them through life’s challenges.

Our ability to easily absorb information when we’re young coincides with the growth of the cortical region (the outermost layer of the brain). Once we pass adolescence, we rely more on previously stored knowledge and genetic factors, and are less influenced by our environment. To better understand the influence of “nurture” and “nature” in the acquisition of cognitive abilities, researchers from more than eight academic institutions looked at how this window in time differed for different individuals. The resulting study, “The Nature and Nurture of High IQ: An Extended Sensitive Period for Intellectual Development,” was published in Psychological Science in 2013.

“Prolonged cortical thickening observed in individuals with high IQ might reflect an extended period of synaptogenesis and high environmental sensitivity or plasticity,” the scholars write. “We tested this hypothesis by examining the timing of changes in the magnitude of genetic and environmental influences on IQ as a function of IQ score.” They based their work on a cross-sectional sample of 11,000 twin pairs and a longitudinal sample of twins, biological siblings and adoptive siblings.

The study’s findings include:

  • IQ development shifts from nurture (environmental) influences to nature (genetic) influences as children move into adulthood, approximately from age 12 to 16.
  • A thicker cortical region, which is associated with higher IQs, also appears to be associated with greater susceptibility to environmental inputs.
  • The time span during which environment plays a dominant role on IQ development is longer for children with higher IQs. “We found that the period of childlike levels of environmental influence was prolonged in higher-IQ individuals, whereas lower-IQ individuals shifted earlier to an adultlike pattern.”
  • Gender does not play a role in the length of time children are able to absorb environmental inputs, and genotype-environment interactions were also ruled out.
  • Assortative mating — the tendency of parents to resemble each other cognitively — was not shown to have a significant influence on the family environment and thus its role in children’s IQ development. In fact, higher-IQ parents were shown to have less assortative mating.

“Our findings raise the question of why a prolonged sensitive period in IQ development might be associated with higher IQ,” the scholars state, and also what the mechanism might be. On the one hand, prolonged immaturity could be beneficial for long-term cognitive development, but on the other, children who eventually have a high IQ score tend to do well early in development. Another possibility is that “heightened levels of attention and arousal, as one may find in individuals of higher IQ, may allow plasticity to occur later into development.”

A related 2011 study, “Verbal and Non-Verbal Intelligence Changes in the Teenage Brain,” found that the IQs of adolescents could shift significantly over time. Study participants were first tested at ages 12 to 16, then again at 15 to 20. One-third of participants experienced a clear change in measured intelligence, with the largest gain being 21 points and the largest decrease 18 points. General intelligence remained relatively constant, while verbal and performance IQ fluctuated due to changes in sensorimotor skills. Also of interest is a 2013 study, “The Stability of Intelligence From Age 11 to Age 90 Years,” which finds that intelligence levels show “moderately high stability from childhood to old-old age.”

Keywords: youth, children, cognition, parenting

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