As you can imagine, this essay will continue with a frank discussion of genitalia and modifications to same.
A eunuch is generally understood to mean a man who has been castrated, i.e. whose testicles have been cut off. Sometimes, though, he has been fully emasculated -- meaning removal of the penis as well; this was usually the case with Chinese eunuchs -- while on other occasions, the term refers to any man who is unable to procreate (e.g. because of impotence or chemical castration), even if he is intact. Unsurprisingly, it can also be slung as an insult against a man, questioning his virility.
We probably got the idea of eunuchs from animal husbandry, where castration of males is common enough that we often have separate terms for the two types: steers vs. bulls, geldings vs. stallions. Among livestock, it brings a number of benefits to their human owners; castrated beasts are less likely to attack people or other males and less likely to break down fences to try and get at females, while the small number of reproductively capable individuals makes it easier to control the population size and arrange for advantageous breeding matches. Neutered animals, female as well as male, also tend to live noticeably longer.
Among humans, the physical effects are similar. The removal of the testicles generally reduces sexual desire and its associated behaviors, while preventing reproduction. If performed before puberty -- as it usually is with animals -- the subject's voice will remain high, he won't grow facial hair or develop male pattern baldness, he'll put on less muscle and retain more fat, and he may wind up tall and long-limbed, as castration interferes with the hormonal changes that stop bone growth. He also stands a good chance of living longer. Males castrated after puberty, by contrast, will generally keep the changes already experienced, though they too will not progress to baldness.
The social effects, though . . . those get very complicated.
Castration or emasculation can be a punishment, not only for the individual, but for the lineage they're no longer able to perpetuate. As such, in a society where a crime taints the whole family, a male criminal might be executed and his sons castrated, stopping the line in its tracks. We've also often seen it as a fitting consequence for sexual crimes -- a category that at times has unfortunately included being gay. Of course, reduction in sexual desire doesn't necessarily mean its elimination entirely, not all sexual crimes are driven by desire in the first place, and there are ways to rape people without functioning testicles (or even a penis). And while there's some evidence that castrated men are less likely to re-offend, it's too scant for us to be sure of a firm causal relationship. Still, in some jurisdictions, convicts are offered a choice between castration (surgical or chemical) followed by release from prison, and serving a longer sentence while keeping their bodies intact . . . and some of them do indeed choose the former.
On the other hand, castration has sometimes been a thing people voluntarily
seek out. Transgender women, of course, may pursue it in the interests of bringing their bodies in line with their self-image. Historically, boys with particularly pure singing voices might either be castrated or undergo a procedure that made their testicles atrophy, so they would retain their childhood range into adulthood; where women were forbidden to sing, these castrati took their place in music. And then in certain places and times, becoming a eunuch could actually be a route to opportunity, wealth, and power.
Though our modern democratic societies tend not to think this way, in cultures more organized around lineages and inheritance, a man who can't procreate is seen as lacking the motivations that drive people to amass power for themselves, their heirs, and their broader kin groups -- meaning that he can be relied upon to serve the interests of his lord instead. In East Asia, eunuch officials were often seen as extensions of the king's or emperor's will, in contrast with scholar-officials who might oppose it. How true this was in reality, of course, depended on the rulers and the officials in question!
That's one kind of trustworthiness; another involves women. Unsurprisingly, eunuchs have also been trusted among sheltered female populations in ways that intact males were not. Probably the most common image of them in the West is as harem guards, because they were less likely to engage in sexual behavior with the women there, and incapable of siring children on them even if such transgressions happened. That's not inaccurate, but it's incomplete, as eunuchs served in a variety of domestic and bureaucratic roles related to such environments. They were the point of contact between male and female worlds, their own liminal status allowing them to cross over into both.
Liminal -- and in many cases, lowly. Eunuchs were commonly servants or even slaves (with castrated slaves sometimes fetching a higher price), and as many of us know from other contexts, high-ranking people easily fall into the trap of forgetting just how much the servants around them are overhearing. Assumed loyalty plus invisible ubiquity makes for a great combination: is it any wonder that eunuchs sometimes doubled as spies? Of course this was not without its dangers; a servant or slave can easily be executed if caught snooping, and that loyalty may not extend in both directions. Still, knowing everyone's secrets and passing them on to the right ears can be a route to power.
Eunuchs didn't only wield power from the shadows, though. In both the Muslim and Chinese worlds, they could also rise to incredibly high rank -- including military rank! The advantage of a eunuch general is that there's not much point in him staging a coup to overthrow the ruler: what's he going to do, start a dynasty that ends when he dies? Few people will flock to that usurper's banner, given that they want stability, not a new civil war a few years or decades down the line. (I do wonder how many of those eunuch military officials were castrated as adults instead of as boys. I suspect more of the former, as they would have the benefits of puberty-induced changes to their bodies -- useful if they're expected to fight personally, instead of just directing the soldiers -- but I don't know for sure.)
In speculative fiction, eunuchs have tended to serve precisely one role: to code a society as a certain kind of "decadent" court, usually modeled on something like Muslim caliphates or the Ottoman Empire. They guard harems, and that's it. But that's been changing a little of late, with characters like the spymaster Varys in George R.R. Martin's A Song of Ice and Fire or the general Ouyang in Shelley Parker-Chan's Radiant Emperor duology, which is historical fantasy set in the transition between the Chinese Yuan and Ming dynasties. Both of those characters are singular, rather than belonging to extensive traditions of eunuch service, but they both reflect genuine dynamics around the roles castrated men can fill that
aren't guarding harems. I doubt we'll see a flood of eunuch characters in Anglophone fiction any time soon -- if only because it's a topic that tends to make a lot of male readers uncomfortable -- but it would be interesting to get some continued variety!

(originally posted at Swan Tower:
https://is.gd/3vKXuV)