A herd of buffalo can only move as fast as the slowest buffalo. When predators attack the herd, they go for the slowest and weakest animals at the back.
This is natural selection at work and it is good for the herd as a whole because its general speed and health is improved by the regular killing of its slowest and weakest members.
In the same way, the human brain is only as fast as its slowest cells. Too much alcohol kills brain cells, but naturally it attacks the slowest and weakest cells first.
Regular consumption of beer eliminates the weaker brain cells, making the brain faster and more efficient.
Which is why you always feel a lot smarter after a few beers.