It's not clear precisely when our ancient ancestors started imbibing, but most likely, ancient hunter-gatherers discovered the effects of alcohol when they found and ate fruit that had dropped to the ground and fermented. Humans liked that tipsy feeling so much that when they switched to being farmers and living in stable communities, they started trying to make the stuff deliberately.
Archaeological chemist Patrick McGovern analyzed shards of clay from a 9,000-year-old Chinese village and found that they contained chemical traces of mead, a wine made from honey. The ancient beverage had an alcohol content of 10 percent [sources: Thadeusz, Gately].
Meanwhile, the potter's wheel wasn't invented until 3,500 years later in Mesopotamia, and wheeled chariots weren't developed until probably 300 years after that [source: Gambino]. So we know, at least, that the earliest mead drinkers didn't have to worry about finding designated drivers.