Evolution of sexually dimorphic longevity in humans

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• That the gender gap in aging is attributable to androgens appears more likely given a recent report of exceptional longevity in eunuchs.

• This scenario predicts that removal of the testes (castration) might extend male lifespan. This possibility is supported by a study of mentally disabled men who had the misfortune to live in the USA in the early-mid 20th century, where sterilization of the “genetically unfit” was common as a result of policies initiated by the eugenics movement [36]. Analysis of mortality data from 297 castrated men, and 735 age-matched intact controls revealed a significant increase in lifespan in the former (70.7 vs. 64.7 yrs, p < 0.001) [37]. If only those castrated earlier in life were considered, the effect on lifespan was more profound: an increase in median lifespan of 11.6 years.

• Notably, the life expectancy of intact control males was considerably lower than that of the general population [37].

• One study compared the lifespans of 50 Italian castratos with a set of intact male singers of the same period, and detected only a 1.2 year increase in mean lifespan in the castratos, that was not statistically significant (65.5±13.8 yrs vs. 64.3±14.1 yrs)

• From such records of the period 1556-1861, 81 eunuchs were identified, with a mean lifespan of 70.0±1.76 years (range 27-109). This compared to mean lifespans of intact men of comparable social status ranging from 50.9-55.6 years, i.e. eunuchs lived 14.4-19.1 years longer than intact men.

• Moreover, three of the 81 eunuchs became centenarians, living to 100, 101 and 109 years, a frequency that is at least 130-times higher than in contemporary developed societies [43].

• This new study confirms the conclusion of Hamilton and Mestler (1969), that the presence of testes markedly shortens lifespan. It is also consistent with the idea that the testes are a determinant of the gender gap in human lifespan.