system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do some languages have upper and lower case letters.
gpt
Actually the reason is a lot simpler than you might think;
Usually languages started out having only upper case letters. That's why on really old professional documents, lower case letters aren't really anywhere to be seen. 
It was only after scribes discovered that they could write much faster and take up a lot less space if they wrote smaller. So they rounded their letters to make them less spacious and soon the lower case letters were made. 
Good question!