Question

Why low temperature is necessary for spermatogenesis?

Answer 1

but I do know that mutation rates are higher when temperatures are higher. Since it's vitally important to keep sperm from mutating or deforming if you want to have normal offspring, then it would make sense to produce them at lower temperature. Evolution seems to have selected for this lower temperature, but why not even cooler temperatures? If processes for sperm production, storage, and function were optimal for temperatures too much lower than the core body temperature, then they would not function optimally or near optimally at the temperatures of the vagina (just speculation there, but based on some fact). Of course we could have evolved to produce sperm at core body temperature but the one thing that evolution would have a very hard time dealing with is the mutation rate. Physics shows that temperature increases mutations. While it may be alright to have very quickly replicating tissues such as intestinal linings have a deformity or a mutation here and there, if that one sperm that has a mutation is the one to fertilize the egg then fitness is severely compromised. It should also be noted that sperm production is not necessarily optimized for lower temperature, but to minimize mutations while maximizing production speed, which happens at higher temperatures. This is why marine mammals have testicles deep inside their body. Mostly unrelated, but that is why elephants have testicles inside their body - they are a mammal that evolved to be ocean dwelling, but has since evolved to be land dwelling again