The Intelligence Paradox: Why the Intelligent Choice Isn't Always the Smart One - Satoshi Kanazawa 2012

Possible Societal Consequences
Why Intelligent People Are the Ultimate Losers in Life

The analysis of the NCDS data suggests that more intelligent women are more likely to remain childless for life and to have fewer children than less intelligent women. If this finding is robust, and is true not only in the United Kingdom but in other western societies as well, what would it mean for these societies? What are the likely consequences of more intelligent women being more likely to remain childless and having fewer children than less intelligent women?

As I explain in Chapter 3, general intelligence is known to be highly heritable.⁷ Genes determine about 80% of the variance in adult intelligence. On average, more intelligent parents beget more intelligent children. And the genes that influence general intelligence are thought to be located on the X chromosomes.⁸ (In fact, as I mention in Chapter 9, they are thought to be located in the same region of the X chromosomes as the genes for male homosexuality, Xq28, which may or may not explain why homosexuals are more intelligent.) It means that boys inherit their general intelligence from their mothers only, while girls inherit their general intelligence from both their mothers and their fathers. Their fathers in turn inherit their general intelligence from their mothers (the girls’ paternal grandmothers) only.

So women influence the general intelligence of future generations very strongly, through their sons and through their paternal granddaughters. If more intelligent women have fewer children and are more likely to remain childless, then one potential consequence is that the average level of general intelligence in society may decline over time.

Throughout the 20th century, the average level of general intelligence in most western industrial nations steadily increased. This phenomenon is now widely known as “the Flynn Effect,”⁹ after two comprehensive reviews of secular increases in average IQ in many western industrialized nations conducted by James R. Flynn.¹⁰ However, Richard Lynn documented the secular rise in intelligence in Japan a few years before Flynn did.¹¹ For this reason, some scientists prefer the name “the Lynn-Flynn Effect”¹² and I adopt the practice here. The first documentation of the secular rise in IQ may date even further back to the 1930s.¹³

Although there is no consensus on what caused the Lynn-Flynn Effect, one likely factor, identified by Richard Lynn himself,¹⁴ is the increasing levels of infant and child nutrition and health. Regardless of their genetic endowment, healthier and better nourished babies on average grow up to have higher intelligence later in life than ill and malnourished babies. These factors likely more than compensated for the dysgenic fertility—where less intelligent parents have more children—throughout the 20th century, and the average level of intelligence has increased in most advanced industrial nations with the improved level of infant health and nutrition.

The improved health and nutrition as potential causes of the Lynn-Flynn Effect, however, would predict that the secular increase in general intelligence would halt in advanced industrial nations. The optimal level of health and nutrition has long passed and now obesity and diabetes have become serious problems in such nations. We are no longer getting healthier and better nourished; we are simply getting fatter in the United States and in other industrial nations.

If improved health and nutrition are chiefly responsible for the secular increase in general intelligence throughout the 20th century, and if these factors no longer contribute to the increase, then the negative effect of the dysgenic fertility should lead to a declining level of average intelligence in advanced industrial nations.¹⁵ This is in fact happening already. There is strong evidence to suggest that the Lynn-Flynn Effect was only a 20th-century phenomenon. It appears to have ended at the end of the 20th century in the most advanced industrial nations (with simultaneously the highest rates of obesity and diabetes). Studies suggest that the average level of intelligence has begun to decline at the beginning of the 21st century in such advanced industrial nations as Australia,¹⁶ Denmark,¹⁷ Norway,¹⁸ and the United Kingdom.¹⁹

Notes

1. Fielder and Huber (2007)

2. Miller 2000a, 2000b, 2009

[3]. I owe this insight to Lena Edlund

4. Kohler, Rodgers and Christensen (1999); Kohler et al. (2006)

5. Miller and Kanazawa (2007, p. 184)

6. Falconer (1960)

7. Jensen (1998)

8. Lehrke (1972, 1997); Turner (1996a, 1996b)

9. Herrnstein and Murray (1994, pp. 307—309)

10. Flynn (1984, 1987)

11. Lynn (1982)

12. Murphy (2011); te Nijenhuis (2011)

13. Merrill (1938)

14. Lynn (1990, 1998)

15. Lynn and Harvey (2008)

16. Cotton et al. (2005)

17. Teasdale and Owen (2008)

18. Sundet, Barlaug and Torjussen (2004)

19. Shayer, Ginsburg and Coe (2007); Shayer and Ginsburg (2009)