The obvious answer is that alcohol kills off stupid brain cells.

According to evolutionary psychologist Satoshi Kanazawa, "more intelligent people are more likely to binge drink and get drunk (Intelligent people are more likely to do stupid things.)"  According to Kanazawa, this phenomenon is consistent with an evolutionary Hypothesis of human behavior:

 Evolutionarily novel entities that more intelligent individuals are better able to comprehend and deal with may include ideas and lifestyles, which form the basis of their preferences and values. It would be very difficult for individuals to prefer or value something that they cannot truly comprehend. So, applied to the domain of preferences and values, the Hypothesis suggests that more intelligent individuals are more likely than less intelligent individuals to acquire and espouse evolutionarily novel preferences and values that did not exist in the ancestral environment and thus our ancestors did not have, but general intelligence has no effect on the acquisition and espousal of evolutionarily familiar preferences and values that existed in the ancestral environment.

Yeah, evolutionary, whatever....a proclivity to do stupid things hardly seems to be an indication of intelligence, which makes one wonder if the study got the definition of 'intelligence' wrong.

Likewise, Kanazawa's Hypothesis would seem to make intelligence maladaptive, leading to a return to instinctual and safer behaviors.

A better explanation is Cliff Claven's "Buffalo Theory" of alcohol and intelligence:

“Well ya see, Norm, it’s like this. A herd of buffalo can only move as fast as the slowest buffalo. So when the herd is hunted, it is the slowest and weakest ones at the back that are killed first. This natural selection is good for the herd as a whole, because the general speed and health of the whole group keeps improving by the regular killing of the weakest members.


The human brain works that way too. It only operates as fast as the slowest brain cells. Excessive intake of alcohol, as we know, kills brain cells. But naturally, it attacks the slowest and weakest brain cells first. So, regular consumption of beer eliminates the weaker brain cells, making the brain a faster and more efficient machine. That’s why you always feel smarter after a few beers.”