One of the interesting facts about being a man is that your gonads simply hang outside your body. This is a quirk which is sure to lead to many memorable events in one’s life.
Positive: You can touch them.
Negative: You can touch them.
Now, as to why this is so I think everyone knows the pat answer: sperm need a lower temperature than body temperature to be manufactured, hence they can’t be internal. If they were in a more comfortable position we would all be infertile and the human race would die out. OK, sounds like a fair trade off, I guess.
But what about sea-mammals? Whales, dolphins, sea lions, etc. have internal testicles, don’t they? AFAIK they have a highly advanced circulatory system for living in cold waters and at extreme depths, so I’m guessing they…have a cold crotch? Or what?
Speaking of evolution, the reason animals acquired warm bloodedness (or homeothermy, or whatever the hip term is nowadays) is so they can be more active, have faster reflexes, and so on. But isn’t becoming so hot that the testes need to descend outside the body a little extreme? I mean really, don’t sperm only have to be a couple degrees cooler? Would we all be that much worse off if we only had a body temperature of 90 F or whatever the threshold is? I guess the answer is yes, as decided by mother nature, but I demand a review.
Sea mammals do have internal testicles. As I recall, blood from the fins is goes to the testicles. The blood is somewhat cooled in the fins which keeps the testicles at a slightly lower temperature than the rest of the body. Someone else can find a cite; I’m too lazy.
Um, well, being a female, I tend to agree with Elaine from Seinfeld; “How do you walk around with all that stuff?”
I don’t know, though I always accepted the temperature theory as plausible. Though it does seem odd that some other mammals, even land-based ones, developed an internal system.
All I know for sure is that males are outies and females are innies, for whatever reason. Makes for some fun diversity.
Then, there is always the theory that when God created humans, She made the male generally bigger, stronger, and more agressive, then left his most sensitive parts hanging out and vulnerable just to even the playing field a bit.
Keeping the body at a constant temperature does more than just make you more active. Where a warm-blooded animal has an intricate chemistry that works wellwithin its internal temperature zone, cold-blooded animals have multiple chemical pathways (or just different catalysts for the same pathways - it’s been a long time since I took the class) to allow main functions to work at several different temperatures. And they need to carry and maintain the genetics that support the multiple pathways/catalysts.
If I had to guess, I’d guess that body temperature settled into the most chemically/genetically easy zone overall, but that some functions had different temperature optima, and that what we ended up with was the result of a multiple-direction tug of war between different body functions. Sadly, the balls were left hanging.
I don’t know about the rabbits, but being so large, elephants have a lower core temperature. The smaller something is, the higher it’s surface area to volume ratio becomes, so small animals bleed heat into their environments faster than large ones, hence the difference in temperature.
Water conducts heat better than air, so getting heat away from your 'nads is easier when in water. And you’ve gotta keep you’re 'nads happy.
I have never quite accepted the temperature theory of why testicles are outside. That is, I understand that sperm do not survive body temperature, but surely that feature evolved as an adaptation to something. Surely we could have evolved sperm that could stand up to body temperature. In fact, we evolved in equatorial Africa where the ambient temperature is often above body temperature for part of the day anyway.
One explanation sometimes offerred is that it prevents sperm from getting stale. I have trouble with that theory too because bees, for example, mate once and the queen then uses the sperm she acquires for the rest of her life (which can, I think, be a few years). You could make a theory based on the need for males to recognize their own offspring, but I would like to see it worked out in detail.
Perhaps it is theoretically possible for sperm to survive higher temperatures than they do but evolution can be clumsy and may not have the line of sight required to get out of the valley. So moving the testicles outside the body seems like a rather drastic change but it must be more straight forward than the alternatives.
Also, I don’t know what the ambient temperature has to do with anything. It may be 110 in the shade, but you’re still body temperature unless you’re on your way to heat stroke. And by the time humans got around the problem was history. The real culprit is some quasi-mammalian reptile / reptilian mammal rat thing whose gonads decided to pack up and leave.
That makes me wonder about dinosaurs and other ancient critters who had high body temperatures. Surely they didn’t have a sac…did they? I guess it’d be impossible to tell. Maybe some of these had some different plumbing to keep their crotches cold as well.
Then again, what about birds? They have pretty high temperatures, don’t they? How do they work it out?
That and, well, I don’t understand how even if sperm getting “stale” was a problem how moving the testicles outside the body would help.
