Does iq get higher with age

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Does IQ Get Higher With Age?

Heritability of IQ and Age: The Wilson Effect

The heritability of IQ, known as the Wilson Effect, increases with age. Studies involving twins and adoption scenarios have shown that the heritability of IQ reaches an asymptote of about 0.80 by the age of 18-20 and remains stable into adulthood. Concurrently, the influence of shared environmental factors decreases to approximately 0.10 by the same age and continues at that level into adulthood. This suggests that genetic factors play a more significant role in determining IQ as individuals grow older.

Stability of IQ Over Time

Longitudinal studies indicate that IQ remains relatively stable over time. For instance, a study involving children aged 5 to 13 years showed that there were no significant changes in IQ scores over three consecutive years. Similarly, the Munich Longitudinal Study on the Ontogenesis of Individual Competencies found that the stability of general intelligence was moderately high from preschool to early adulthood, with higher stability observed for shorter intervals between measurements and increasing stability with age. These findings suggest that while individual IQ scores may fluctuate slightly, they generally remain consistent over time.

Impact of Early IQ on Later Life Outcomes

Higher IQ in early life has been associated with various positive outcomes in later life. For example, individuals with higher IQ scores in adolescence tend to feel younger subjectively in old age, a phenomenon mediated by higher openness. Additionally, higher early-life IQ is linked to lower mortality rates in middle to late adulthood, suggesting that cognitive ability in the first two decades of life can have long-term health benefits. Furthermore, early-life IQ can buffer the effects of adverse environments on physical and mental health in old age.

Cognitive Reserve and Terminal Decline

The cognitive reserve hypothesis posits that individuals with higher IQs can better tolerate age-related brain pathologies, delaying the onset of terminal cognitive decline. However, once decline begins, it tends to be steeper for those with higher IQs. This indicates that while higher IQ may provide a temporary buffer against cognitive decline, it does not prevent it entirely.

The Flynn Effect and Age Variations

The Flynn Effect, which describes generational increases in IQ scores, does not apply uniformly across all ages and ability levels. A study of 10,000 US adolescents found that while IQs increased by 2.3 points at age 13, they decreased by 1.6 points at age 18. Additionally, IQs decreased significantly for those with lower ability levels but increased for those with higher ability levels. This suggests that the Flynn Effect is more complex than previously thought and varies significantly depending on age and cognitive ability.

Changes in Brain Structure and Intelligence

Changes in cortical thickness and surface area over time are related to intelligence. More intelligent children tend to have a thinner cortex at age 10, which thins faster over time. However, by age 42, a thicker cortex is associated with higher intelligence. Additionally, the cortical surface area expands during adolescence and then decreases at a higher rate in more intelligent individuals. These findings indicate that intelligence is closely linked to the timing and magnitude of changes in brain structure during development.

Conclusion

In summary, while the heritability of IQ increases with age, individual IQ scores remain relatively stable over time. Early-life IQ has significant implications for later life outcomes, including subjective age and mortality risk. The cognitive reserve hypothesis suggests that higher IQ can delay cognitive decline, although it does not prevent it. The Flynn Effect varies by age and ability level, and changes in brain structure are closely related to intelligence. Overall, these findings highlight the complex interplay between age, IQ, and cognitive development.