re: Electromagnetic spectrum
I've read that people who have had corneas removed for one reason or another can see further into the ultraviolet than normal (but not by much). As for our focal range, I speculate that by the time we became plains dwellers, our primate eyes had pretty much evolved to where they are now, and the need to see things clearly miles off wasn't an issue before that. I read elsewhere that some tribes who have spent their entire existence in deep forest actually have trouble working with long distance vision, perceiving distant objects as simply small things closer up.