A Discussion about Testicles
Some colleague in Australia wanted to know from me once what my view was on Adolf Hitler’s condition of ”having had only one ball” (= one testicle). I knew nothing about this, but later learned that many people believed that to be true. And so it was (in a way), for according to a report by Prof. Peter Fleischmann in 2015, based on the medical records of Hitler’s health, the man had suffered from an undescended right testicle. Medically this does not mean he had only one testis; it only means that just one was externally visible. Surgically, of course, it is sometimes necessary to remove one (or even both) and historically eunuchs, men in other words who for whatever reason were bereaved of their testicles, come to mind. I remember having read once that some tribal people practiced the ritual removal of one testicle, but despite a thorough investigation involving internet search engines, I could not locate the source of that information and wonder if a reader can perhaps help and find evidence in support of that claim. However, what is well documented is that in most men the left testicle is bigger than the right one and that the Greeks of the antiquity (wrongly) believed that sons were “made” by the right and girls by the left testicle.
Anyway, I want to devote this blog to the structure that males cannot be without: their testes (also known as testicles). If men can be fertile with just one testicle externally visible (whether the other is missing altogether or simply undescended as in Hitler’s case), why do these structures in most but not all mammalian males, dangle on the outside of the body in their little scrotum bag? Amongst bats, insectivores and rodents it is common to find that the testes migrate from the inside of the body into a scrotum during the mating season; afterwards they move back to their hidden location inside the body. But elephants and other mammals known as Afrotheres, which also include elephant shrews, tenrecs, aardvarks, hyraxes, sea cows and several extinct groups, all possess testes that never – not even during the mating season – become externally visible and constantly remain hidden and protected inside the male’s body. In whales the testes are permanently internal and that would probably make sense if one considers hydrodynamic drag and having to swim with a dangling scrotum.
A widely accepted theory, for which good experimental evidence exists, postulates that higher internal body temperatures are damaging to the spermatozoa. But this does not square with the examples of species given above that don’t have an externally placed scrotum with testicles in them. Besides, if temperature is so deleterious to sperms, why do all bird species have their testicles inside their bodies, even a bird’s body temperature is usually higher than that of a mammal? The discovery of “testicle descent genes” in the Afrotheres species has recently been announced. This suggests that during evolution these genes either mutated or were inactivated and consequently prevented that the testes descended in Afrotheres. But did their spermatozoa suffer or become damaged? It doesn’t look like that and it seems that protecting the sperm-making structures from physical damage was of greater concern than preventing effects that the higher internal body temperature might possibly cause. Could, therefore, the evolutionary older testicular descendence have had a different function?
That is possible, because in species that exhibit a seasonal testicular “out-and-inward” migration, the appearance of a voluminous scrotum could be a sexual signal, especially if combined with an attractive colour. A permanent display of maleness through externally visible testicles could have been the reason why in most mammalian species the testes are not retained inside their bodies. In humans, following ejaculation, testes are sometimes temporarily retracted into the body cavity: a case of an atavism? An echo from the past? Or a sign of what is still to come?
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