"Unlike most other parts of your body, though, your scrotum lacks protection in the form of bones, large muscle mass, and fat. The testes are just wee little glands, and they’re going to absorb the whole force of the blow all on their own.
Another thing that makes a ball shot so painful is the same thing that makes almost every other sensation down there so much fun. Your groin has a ridiculously high number of sensory nerve endings, and such generous innervation makes good and bad touches alike very noticeable sensations."
But seriously Bardos when was the last time this happened to you? What went wrong?
If you damaged your gonads to the point that you could not reproduce, then that’s you out of the genepool (unless you had previously reproduced). Natural selection would strongly favour those who have heavily innervated gonads. Particularly for bipedal species, where they are less protected.
(Note: for some kinds of dangerous stimuli a knee-jerk style response could be evolved instead of pain. But there is no simple knee-jerk response appropriate to defending the nuts)
One thing to be aware of however is that there are different kinds of nerves for sensory touch and pain. It doesn’t follow that because an organ is sensitive to touch that it must be sensitive to pain.
Can’t speak for Bardos, but it happens (though not usually as a kick, at least not for me). I’ve been whomped in the crotch by a soccer ball and a raqcuetball before. More recently I borrowed a friend’s motorcycle; I was unfamiliar with the shape of his particular bike, so when I settled down in the saddle, I inadvertently crushed my grapes against the fuel tank.
I have to imagine that if you could reach in and thwack any other internal organ with the same amount of force, it would hurt just as bad. But if you were in a situation where your kidneys were hanging out of your body like that, their sensitivity would probably not be your largest concern.
I’ve been babysitting for the past year or so and discovered that a 6 year old’s testicles aren’t sensitive at all. There is all manner of crotch punching going on at the playground and he says it doesn’t hurt. Is this normal? At what age do they become sensitive?
The “testicles are outside the body for temp control reasons” argument may not be accurate. I recently read (I think it was in Mary Roach’s Bonk, but it could have been a magazine article) that while testicles outside the body (TOB) have evolved twice in mammalian lineage, there are mammals which keep their testicles inside the body (TIB). TIB mammals produce sperm at body temp with no problems at all. There were also, IIRC, a couple of species which had changed from TOB to TIB and had no ill effects.
The downside is that it’s looking more and more like TOB is a form of sexual selection. So, TOB are the equivalent of peacock tails and stag antlers. Look out, gentlemen. In another 10,000 generations, you may be dragging your testicles on the ground.
Well, why does pain exist at all, other than as a means of warning / deterring the organism?
Again though, there are different kinds of nerves and there is no reason why our gonads could not be very sensitive to touch but quite insensitive to pain (and in fact there are different kinds of nociceptors, so a tissue could be sensitive to, say, hot and cold, but not blunt trauma).
In humans we only really have good examples of organs that are sensitive to one or more forms of pain and insensitive to touch, but not the other way round. But anyway the two things are not coupled.
It’s not always that much pain. In many situations you won’t feel pain at all from physical harm such as a sharp blow. Martial artists say they can tolerate the pain of a low blow but I’ve never heard one say they don’t feel it.