A herd of buffalo can move only as fast as the slowest buffalo. When the herd is hunted, it is the slowest and weakest ones at the back that are killed first.
This natural selection benefits the herd as a whole, as the general speed and health of the group improve through the regular culling of the weakest members.
Similarly, the human brain can only operate as fast as its slowest brain cells.
Excessive intake of alcohol kills brain cells, and it naturally attacks the slowest and weakest ones first.
Thus, regular consumption of beer eliminates the weaker brain cells, constantly making the brain a faster and more efficient machine.