Having a newborn son raises all sorts of interesting questions. During several examinations the doctor checked to make sure his testicles decended correctly - this makes me wonder why they need to be outside in the first place.
I know that right now the testicles have to be outside the body because sperm require slightly cooler temperatures in order to develop properly - but it seems it would make more sense for the testicles to be safe inside and able to produce sperm at normal body temperature.
Is there any evidence why it ended up this way? Is it that there was just no evolutionary pressure to go one way or the other? Or things just never mutated in a way where it would be an option?