Testicle Size in Parenting and Sexual Selection


Thanks goes to Laura Deming for pointing out another recent paper whose title, “Testicular volume is inversely correlated with nurturing-related brain activity in human fathers,” proved irresistible to PNAS, enabling them to overlook stunning intellectual flaws. 

Problems include: Selection bias. Participants were self-selected by reading ads and fliers, then deciding to participate in a parenting study. If the father was not cohabiting with the mother, he was disqualified. This removed from the study pool an important number of fathers who give no care to their children, do not answer ads about parenting studies, and who do not cohabitate with the mother of their children. Having eliminated the crucial bottom end of the study population, the authors then lopped off the much more interesting top end – fathers who do not cohabitate with the mother but provide 100% of the care and support for their children – yes, single dads do exist.

Now stuck with this muddle-in-the-middle study population, the authors compounded the error by failing to control for age. The parameters they studied – testosterone level and testicular volume – are linearly related and decline proportionately by up to 50% in the population of males between ages 21 and 55 that they studied. This resulted in a series of scattergrams that, quite bluntly, do not support either their title or their conclusions.

Most important, this study fails the “Duh” test. The average testicle of 40cc is not a significant metabolic drain. Enlarging it by 2 standard deviations to 65cc is not a large investment. But it is difficult to imagine why a male would grow a testicle of 65cc when instead he could have added 25cc of gray matter to the area of his brain devoted to figuring out what women want. If he is a social moron, it is unlikely he will ever get to use his large testicles. More important, simply possessing them exposes him and his evolutionary strategy of parental non-involvement to his potential mates. The Life History Theory these authors were hoping to probe makes it clear that human females are crucially dependent on the support of their mate for successful reproduction. If women could determine accurately whether a possible spouse would be a helpful and attentive partner by simply feeling his balls, then women in barroom dating scenes would have their hands under the table, not fiddling with cigarettes or shot glasses. Women would frown at anything resembling a bulge in a man’s pants, and men would be binding their privates in an effort to conceal unsightly testicular volumes.

Let’s do a quick study. Not a careful scientific one – let’s just work at the level of members of Departments of Psychiatry and Anthropology publishing in PNAS. Women readers are encouraged to fill out the attached survey, which is designed to determine whether female humans pay any attention to the “fact” that the most committed, nurturing fathers have the smallest testicles.

Use this link to access the survey: https://www.surveymonkey.com/s/testesblog

View the original blog post, Science is Not Your Enemy

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