My friend Brian sent me a link to a CBS News article titled Eunuchs outlive male counterparts, study of Korean dynasty finds.What’s the mechanism? he asked. Why do you care? I thought. Suppose having testicles shortens your life, are you going to cut them off just to live longer? And doing it on the basis of an article on CBS News? It would qualify for the Darwin award.
Once I got over the endless scenarios for a joke ( “An old guy comes to the bar…”) I was wondering: what could be the mechanism? Curiosity got the better of me. I read the article and then read the original scientific publication (Current Biology, Sept. 24, 2012).
The authors, Kyung-Jin Min, Cheol-Koo Lee, and Han-Nam Park of INHA University and Seoul University in South Korea, had a unique Korean resource to study the effect of castration, and by implication of testosterone, on longevity.
A eunuch is a castrated human male, and historically, eunuchs have been employed as guards and servants in harems across the Middle East and Asia. The Imperial court of the Korean Chosun Dynasty (1392–1910) also had eunuchs. Eunuchs of the Chosun Dynasty lived with privileges: Korean eunuchs were conferred with official ranks and were legally allowed to marry. Married couples were also entitled to have children by adopting castrated boys or normal girls. The boys lost their reproductive organs in accidents, or they underwent deliberate castration to gain access to the palace before becoming a teenager. Although the family of a eunuch was composed of non-blood-related members, the bonding in these families is believed to have been as strong as that in traditional blood-related families.
A genealogy record of Korean eunuchs contains the records of 385 eunuchs. From these records, the lifespans of 81 eunuchs could be identified. These were compared with the lifespans of 3 families of the same socio-economic status that lived in the same period.
The results were quite striking. The average lifespan of the eunuch group was 70.0 ± 1.76, compared to 50.9-55.6 of the non-eunuch families.
The authors point out another interesting finding: out of the 81 eunuchs, three were centenarians, aged 100, 101, and 109 years. The current incidence of centenarians is one per 3,500 in Japan and per 4,400 in the United States. Thus, the incidence of centenarians among Korean eunuchs is at least 130 times higher than that of present-day developed countries.
Evolutionary scientists have noticed that in many species there is an inverse relationship between reproduction and lifespan: species that reproduce early and often tend to have a shorter lifespan. This gave rise to the disposable soma theory. The theory posits that resources are competitively allocated between somatic repair and reproduction and that somatic aging occurs at the expense of reproduction. It makes perfect evolutionary sense: the more offspring the more competition for resources, the better it is for the survival of the species if the oldsters simply clear the stage. As cruel as it may sound, they are disposable. Nice theory, except that it raises the issue of the chicken and the egg. Does reproduction cause shorter life, or just as plausibly, does inherently short lifespan of a species make it evolutionarily advantageous to generate multiple offspring in a short time?
We could come closer to the answer by examining the biological mechanism that operates in testicularly-challenged eunuchs?
The downside of testosterone
Testosterone is associated with atherosclerotic cardiovascular disease. Since heart disease was probably a major cause of death among the privileged, this would be my prime suspect to explain the longevity advantage of the Korean castrati.
There could be a behavioral cause as well: testosterone increases aggressive behavior with its attendant consequences: untimely death in brawls and battles.
Be it as it may, Brian, as much as you’d like to live to a ripe old age –parting with the crown jewels is a stiff price to pay, in my humble opinion.