Drug May Repair DNA at Earliest Stages of Alzheimer’s – And it’s Already Passed Safety Trials
(www.goodnewsnetwork.org)
Natural selection was always the cruelest way to manage disease. It requires us to be struggling to survive. When a significant proportion of humankind have died from a disease, we may evolve a resistence to it, but that's a brutal price to pay. We're past that, and good riddance to it.
But you chose a strange place to bring that up. A drug to prevent Alzheimers won't have much effect on natural selection, since a susceptibility to Alzheimers would very rarely prevent successful reproduction. Alzheimers is strongly tied to the ageing process, which is probably an evolved characteristic in itself. Natural selection was never a friend to the elderly.