One of the theories on alcohol is mead (honey wine) was the first alcohol. Supposedly hunters would throw a bit of honey into their water skins and go hunting. When they came back, they might not have finished it and when used again, it was alcoholic. Eventually they noticed the effect and enjoyed it.

I'm sure after that much experimentation was had on different carbohydrates.

Beer seems hard though. You have to boil it just right to make it right, before you even start fermentation.