The Limitations of IQ and the Importance of Mental Character

Key Insight

Intelligence Quotient (IQ) scores are reasonably predictive of academic performance, with individuals scoring above 100 generally benefiting in business and those above 120 in fields like nuclear physics. Research shows that a person's childhood IQ scores are consistent into adulthood, and proficiency in one intellectual skill, such as verbal analogies, often correlates with strengths in others like math problem-solving or reading comprehension. This ability to perform well on such tests is significantly influenced by heredity, with a mother's IQ being the strongest predictor of her child's score.

Despite its predictive qualities in academic settings, IQ is surprisingly malleable. Environmental factors significantly shape it; for instance, a study of Black children in Prince Edward County, Virginia, found a loss of 6 IQ points for every missed year of school. Parental attention also matters, as firstborns tend to have higher IQs. The Flynn Effect provides broad evidence of this malleability, showing that IQ levels in the developed world rose by about 3 percentage points per decade between 1947 and 2002, primarily due to improved abstract reasoning skills, not vocabulary or reading comprehension. However, beyond school, IQ is not a reliable predictor of success. People with high IQs do not necessarily have better relationships, marriages, or parenting skills. Studies indicate IQ predicts only about 4 percent of variance in job performance and contributes at best 20 percent to life success.

Once an individual's IQ surpasses approximately 120, additional intelligence provides little measurable benefit for lifetime success. For example, the Terman study of high-IQ individuals (135 or above) found they did well as lawyers and executives, but produced no superstar achievers; those who excelled had superior work ethics and ambition, not significantly higher IQs. Furthermore, a study of 7403 Americans found no correlation between accumulating large wealth and high IQ. True real-world performance requires 'mental character', which encompasses dispositions like gathering information before deciding, seeking diverse viewpoints, thinking extensively, calibrating opinions to evidence, considering future consequences, weighing pros and cons, and seeking nuance. While IQ excels at solving well-defined problems with given rules, mental character is essential for identifying problems and formulating rules, demonstrating why many intelligent individuals fail due to a lack of noncognitive traits like motivation and self-discipline, or self-destructively overestimating their intelligence, such as investors who lost 31.6 percent in a fund despite its 16 percent annualized return.