And, amazingly enough,
At any given time, in some specific population, it is selecting weakerer, or dumberer, or slower, or less armored, or more randomly being grabbed as a shark's meal.
Actually, that's false. The "true" lawyerly reposte would be that at any given time, somwhere, somehow stronger is not being selected (because smarter or faster is), or smarter is not being selected (because armored is), or faster is not being selected (because some other specialization is the key), etc. At least, I can think of no likely positive advantage in genuine incapacity.