The most common treatment for alzheimer's disease is to give drugs that stimulate

that stimulate the production or no destruction of Acetylcholine.

There are a lot of hypothesis of what is the cause of Alzheimer's disease  but one of the most common ones, is that the disease is caused by insufficiency in the synthesis of the neurotransmitter acetylcholine. Drugs that increase its production or inhibit enzymes that destroy acetylcholine are very used to decrease symptoms.

It is evolution, because we all have some of the same traits like eye color or shape or ears.