Alcoholic factoid

I have just read in a news item written by one Sarah C. P. Williams in an online magazine that flies under the AAAS banner, that our ability to metabolize alcohol is down an ancient mutation to do with something called ADH4. The selective advantage of which was that it enabled us to manage with fallen and partially rotten fruit when we came down from the trees and no longer had such ready access to the fresh stuff. It was no good being drunk in the jungle, red in tooth and claw as it was, so we needed the mutant ADH4 so that we could both eat the rotten fruit and burn the alcohol off.