Rule of thumb, here: Mutations tend to persist in a species if they meet one of two criteria. Either they are adaptive and help an individual to survive (big brain, opposable thumbs) or they are so inconsequential as to have no effect (male pattern baldness, rollable tongue). Mutations that are bad for you tend to go away pretty quickly. Now, alcohol rots your liver, makes you stupid and lazy, gets you into fights that aren't worth winning. So why do so many humans tolerate, even crave, this toxic fluid? Anecdotal evidence suggests that it may convey an important reproductive advantage.