In the past few years, Satoshi Kanazawa, a reader in management and research methodology at the London School of Economics, published a series of papers in the Journal of Theoretical Biology with titles such as “Big and Tall Parents Have More Sons” (2005), “Violent Men Have More Sons” (2006), “Engineers Have More Sons, Nurses Have More Daughters” (2005), and “Beautiful Parents Have More Daughters” (2007).
Figure 1. In 1973, Robert Trivers and Dan Willard hypothesized that sex ratio (boy births to girl births) was responsive to heritable traits that are selectively more advantageous to offspring of one sex than the other. Factors that affect sex ratio (race, maternal health and others) have been studied frequently. Any effects found are small—typically less than one percent. A series of recent sex-ratio studies reported much larger deviations, including a report that attractive parents were 26 percent less likely to have a son than a daughter as the first child. Published analyses followed, documenting methodological flaws in the studies and shrinking the findings below the level of statistical significance. The question arises: What is to be made of results that are suggestive but statistically insignificant, especially in an era when statistically insignificant findings may be widely reported as news?
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