The Sheep Theory
A herd of sheep can only move at the speed of the slowest sheep. When the herd is chased, the slowest and weakest are attacked first. This natural selection is good for the herd in general, because the speed of the herd increases as the slower and weaker ones are eliminated.
In the same way, the human brain can not function faster than its slowest cells. As we know today, alcohol consumption destroys brain cells.
Of course, the slowest and weakest cells are destroyed first. It can therefore be deduced that the consumption of alcohol eliminates the weakest cells, thus making our brain more and more efficient.
Which explains why you always feel a little smarter after 4 or 5 beers.