Can iq increase with age
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Can IQ Increase with Age?
Heritability of IQ and Age: The Wilson Effect
The heritability of IQ, which refers to the proportion of IQ variance attributable to genetic factors, has been shown to increase with age. This phenomenon, known as the Wilson Effect, indicates that genetic influences on IQ become more pronounced as individuals grow older. Studies involving twins and adoption scenarios reveal that the heritability of IQ reaches approximately 0.80 by the age of 18-20 and remains stable into adulthood. Concurrently, the influence of shared environmental factors diminishes significantly, stabilizing at around 0.10 by the same age range.
IQ Stability and Changes in Specific Populations
Research on children and young adults with Duchenne muscular dystrophy (DMD) indicates that while overall IQ scores may not show significant age-related changes, specific components such as Verbal IQ can increase with age. This suggests that certain cognitive abilities may develop or improve over time, even if the general IQ remains stable. Similarly, studies on individuals with phenylketonuria (PKU) show that IQ levels tend to stabilize after the age of 10, provided that dietary management is maintained.
Cognitive Reserve and Terminal Decline
The concept of cognitive reserve posits that individuals with higher IQs can better withstand age-related brain pathologies, delaying the onset of cognitive decline. Research supports this hypothesis, showing that higher IQ is associated with a delayed onset of terminal decline in cognitive abilities such as perceptual and motor speed, and verbal ability. However, once cognitive decline begins, it tends to progress more rapidly in individuals with higher initial IQs.
Brain Structure and IQ Development
Changes in brain structure, particularly cortical thickness and surface area, have been linked to IQ development. In children, a thinner cortex is associated with higher IQ, and this relationship becomes more pronounced with age. By young adulthood, a thicker cortex correlates with higher intelligence. Additionally, the cortical surface area expands during adolescence and then decreases, with more intelligent individuals showing faster completion of this expansion and subsequent reduction.
The Flynn Effect and Age Variability
The Flynn Effect, which describes generational increases in IQ scores, does not uniformly apply across all ages and ability levels. For instance, while younger adolescents may show IQ gains over time, older adolescents and those with lower initial IQs may experience declines. This variability suggests that the Flynn Effect is influenced by a range of factors, including age and cognitive ability.
Brain Aging and Cognitive Stability
Longitudinal studies on older adults indicate that while there is significant age-related decline in brain structures such as grey matter and white matter, these changes do not necessarily correlate with declines in IQ. Verbal and non-verbal IQ measures tend to remain stable despite neuroanatomical deterioration, suggesting that cognitive abilities can be maintained even as the brain ages.
Conclusion
In summary, while general IQ may not significantly increase with age, specific cognitive abilities and components of IQ can show improvement. The heritability of IQ becomes more pronounced with age, and higher IQ can provide a cognitive reserve that delays the onset of cognitive decline. Changes in brain structure also play a crucial role in IQ development, and the Flynn Effect varies across different age groups and ability levels. Overall, the relationship between age and IQ is complex and influenced by a multitude of genetic, environmental, and neuroanatomical factors.
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