The relationship between intelligence and its genetic and environmental basis has been widely debated in the scientific literature. The study conducted by Brant et al. (2013) offers a robust and innovative contribution by proposing that individuals with high intelligence quotient (IQ) present an extension of the sensitive period for intellectual development, during which the brain maintains greater plasticity and receptivity to environmental stimuli.
The central hypothesis of the research is that intellectual development not only follows distinct trajectories among individuals with different IQ levels, but that these trajectories are marked by a temporal shift in the predominance of environmental and genetic factors. Using a cross-sectional sample of almost 11,000 pairs of twins and a longitudinal sample composed of twins, biological and adoptive siblings, the authors used DeFries-Fulker regression to estimate the shared genetic (h²) and environmental (c²) influences on IQ, and to examine how these influences vary according to IQ level and age.
The data reveal an interesting pattern: individuals with higher IQs maintain significant environmental influences into adolescence, while those with lower IQs transition early into an adult pattern characterized by greater heritability and less influence from the shared environment. This finding suggests that for the more intelligent, the window of environmental sensitivity is extended, allowing for greater integration of experiences in the refinement of cognitive abilities (Brant et al., 2013).
This effect was most clearly observed in the adolescent group (13–18 years), in which there was a positive correlation between IQ and environmental influence (β = 0.12; p < 0.001), and a negative correlation between IQ and heredity (β = −0.14; p < 0.001). Interestingly, this association disappears in childhood and adulthood, reinforcing the hypothesis of a specific temporal window of plasticity modulated by the level of cognitive ability.
Another notable finding is that individuals with high IQs show later changes in etiological influences, with the transition from environmental to genetic dominance occurring between adolescence and adulthood. Those with lower IQs, on the other hand, undergo this transition between childhood and adolescence. This pattern indicates that the period of greatest receptivity to environmental stimuli—and therefore of greatest potential for cognitive change—lasts longer for the most intelligent.
This prolongation of the sensitive period can be compared to the pattern of cortical development observed in individuals with high IQ, who show prolonged thickening of the cortex in frontal and temporal regions—a morphological marker that reflects continuous synaptogenesis and high plasticity (Shaw et al., 2006). This convergence of behavioral and neuroanatomical evidence supports the idea that high intelligence is associated with more prolonged and malleable brain development.
However, the authors acknowledge that the mechanism responsible for this extension of the sensitive period is still unclear. Theories such as the active genotype-environment correlation, which proposes that individuals shape their own environments according to their genetic traits, do not satisfactorily explain the delay in the increase in heritability among high IQ individuals. Alternatives, such as the amplification of existing genetic variations and the role of synaptic pruning, have also been discussed as potential explanations.
The study by Brant and colleagues marks an important advance in understanding the foundations of intellectual development. By showing that cognitive plasticity varies not only with age but also with level of intelligence, it provides empirical foundations for personalized educational policies, especially during adolescence. This phase appears to be a critical window for intervention to allow high cognitive potentials to flourish, provided that its differential extent among individuals is recognized.
In short, high intelligence would not only be a reflection of superior genetic predispositions, but also the result of a brain that remains receptive to environmental influences for longer. This prolonged plasticity can be seen as an adaptive trait, expanding the horizon for more effective and personalized educational and neuropsychological interventions throughout development.
Reference :
RUBIN, Kenneth H.; COPLAN, Robert J.; BOWKER, Julie C. Social withdrawal in childhood. Annual Review of Psychology, vol. 60, p. 141–171, 2009. DOI: 10.1146/annurev.psych.60.110707.163642.
