Is Raising IQ Possible?

When we believe intelligence stems mainly from hereditary factors, we tend to view it as unchangeable (Zimbardo, Johnson, & McCann, 2017, p. 221).

Chapter 11 noted that intelligence heritability for adults in favorable environments in developed nations approaches .80. Such elevated h² values indicate that variations in adult IQ scores correlate strongly with genetic differences. This reality can make people—like the textbook authors quoted above—pessimistic about improving intelligence. The reasoning follows this pattern:

This chapter explores the weaknesses in this reasoning. That said, I approach this as a realistic optimist. My analysis of heritability demonstrates that it does constrain environmental influence. Nevertheless, substantial heritability doesn't eliminate the potential for environmental modifications that can boost intelligence—sometimes considerably.

High Heritability and Effective Interventions. Two classic cases demonstrate traits with strong heritability that respond well to environmental intervention. First is myopia (nearsightedness), which shows remarkable heritability—.75 to .88 in one representative study (Dirani et al., 2006). Yet straightforward interventions correct this highly heritable condition: eyeglasses and contact lenses. Therefore, environmental modifications can enhance functioning even when traits show high heritability.

The second case involves phenylketonuria (PKU). Individuals with PKU cannot process phenylalanine, an amino acid present in chicken, egg whites, nuts, certain seafood, potatoes, and numerous common foods. PKU results from inheriting two defective gene copies on Chromosome 12; everyone possessing both defective copies develops PKU, meaning h² equals 1. Without treatment, PKU causes intellectual disability and neurological complications as children mature. However, following a specialized low-phenylalanine diet allows people with PKU to develop typically. This further proves that strong heritability doesn't doom people to their genetic fate.

Successful Interventions to Raise IQ. While myopia and PKU show that high heritability permits effective treatments, this doesn't automatically apply to intelligence. Myopia has straightforward causes and simple remedies. PKU involves a single gene with discovered biochemistry leading to effective treatment (Kevles, 1995). Intelligence appears far more genetically and biologically intricate than these examples, likely involving thousands of genes.

Still, progress exists in finding methods to enhance intelligence. One major success began in the 1970s when researchers observed that children with elevated lead levels scored 4–5 IQ points lower than those with minimal lead exposure. This persisted even when high-lead children seemed healthy without obvious poisoning symptoms. These differences remained after accounting for family variables like socioeconomic status and parental educational attitudes (de la Burdé & Choate, 1975; Landrigan et al., 1975; Needleman et al., 1979). Consequently, the U.S. government reduced lead exposure by banning lead in paint, cookware, toys, and children's products in 1978, in new plumbing in 1986, and in gasoline by 1996.

Americans now have reduced body lead concentrations. In 2016, merely 0.50% of American children had blood lead levels of 10 μg/dL or above, and 3.5% had levels of 5 μg/dL or higher (Centers for Disease Control, 2018, p. 8). During this period, intelligence test scores increased approximately 9–12 points in America, though lead reduction alone doesn't explain this rise. Lowering childhood lead levels likely increases IQ, yet no safe lead level exists (Huang et al., 2012).

Another effective intervention addresses iodine deficiency. Iodine supplements cure deficiency and raise children's IQ by roughly 8 points (Protzko, 2017a). Two billion people globally suffer iodine deficiency, primarily in southern Asia and Sub-Saharan Africa, risking lower IQ and intellectual disabilities. Indeed, iodine deficiency causes the most common preventable intellectual disability worldwide. Treatment costs merely 2 to 5 cents annually per person, making it the most economical intelligence-raising method. The typical approach involves adding iodine to salt (M. B. Zimmerman, Jooste, & Pandav, 2008).

These examples prove high heritability doesn't preclude effective interventions. Theoretically, however, the paradox persists: heritability demonstrates genetic importance, yet substantial IQ changes occur. How do these coexist?

The answer lies in the statistical foundations of h² and intervention effects. Heritability relies on variance, while intervention effectiveness depends on averages. Averages measure typical scores in samples, whereas variance measures score differences (Warne, 2018). Since these statistics measure different sample characteristics, genes can affect IQ variability (through heritability) while environmental treatments impact averages. These two IQ influences operate independently.

This example reminds us that heritability gauges genetic influence under present environmental conditions; alter that environment sufficiently, and traits may change. Height demonstrates this—highly heritable (h² between .87 and .93 for men, .68 and .84 for women; Silventoinen et al., 2003), yet adults today exceed past generations in height (Komlos, Hau, & Bourguinat, 2003; Komlos & Lauderdale, 2007). Improved nutrition and healthcare haven't diminished genetic importance in determining height differences within current populations.

Similarly, IQ scores far exceed those from early testing days (Flynn, 1984, 1987; Pietschnig & Voracek, 2015). Chapter 14 explores this increase further. The crucial message: IQ scores reflect genetic influence (shown by high heritability) while environmental changes—like decreased lead exposure or proper PKU diets—can also elevate IQ.

Untreated PKU, lead poisoning, and iodine deficiency share one commonality: all severely harm intelligence (Hunt, 2011), despite strong genetic influence where h² approximates .50 in many studies. This chapter's examples demonstrate that environmental variables powerfully influence heritable traits—including intelligence. Through significant environmental changes, individuals can experience remarkable IQ improvements. However, not every treatment matches the effectiveness or affordability of these interventions. Chapters 14–16 discuss limitations of other proposed IQ-boosting interventions for healthy populations.




From Chapter 12 of "In the Know: Debunking 35 Myths About Human Intelligence" by Dr. Russell Warne (2020)