system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can we see veins on the outside of our body but not arteries?
gpt
Arteries tend *not* to be on the outside of the body, because if they're damaged it is much more dangerous than witha vein, due to the higher pressure. So evolution strongly favours moving arteries to the inside of the body as much as possible.