system
Given the following post, respond as if you're commenting on Reddit:
human
Why did evolution through natural selection favour putting testicles in a scrotum rather developing more heat resistant sperm.

I understand that as things are currently sperm production and storage is optimal at below body temperature, but am wondering what evolutionary pressures would have favoured the current system over developing tetes which worked best at body temperature.

What forces triggered the development of external testes in the first place?
gpt
Probably just the testes were slightly external by some mutation, and this  gave slightly higher sperm survival rates and it snowballed from there. However your phrasing of the question suggests that you are thinking of evolution as making concious choices. The only real reason that evolution 'picks' one solution over another is if it happened first, by chance. It is pretty much impossible for it then to go back and pick a better solution, since going back would be less favourable (or the change would never have happened in the first place).