system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we have so many different races that are so unique (black,white,indian,asian,hispanic). I know it was evolution but how/why ?

This question is for my 8 year old I tried to explain the best I could and why do asians have squinted eyes, why are black people black. Most of the googling I did just explained human evolution and not the race part of it. I know you guys can explain this way better than any article I could find and summarize.
I apologize in advance for my grammar I am not very book smart.
gpt
Human populations in various parts of the world have been largely isolated from one another; it wasn't all that common than a Chinese man wed an African woman or whatever. Gene pool mixing was minimal between what we now consider the racial boundaries. 

Over time evolution change the local population in relatively minor ways as compared to the difference between humans and chimapanzees, say, but nonetheless visible ways. Some were actually adaptations like the melanin content thing; the darker skinned humans can handle sunlight far better than can the pale. Pale skinned humans, though, absorb vitamin D from sunlight much more easily.

This worked well considering the climates you got your more pale and more dark skinned folks in.

Plenty of the difference aren't adaptations so much as just non-destructive mutations. There's plenty of cosmetic affairs that don't really make a difference to survival.