well, rats evolve into rats, and sharks evelve into sharks; which is to say that they have their own slot which they fill to perfection, and when they do evelove it is into a better form of rat or shark... The same is true of Amoeba, that no matter how many critters evolve from amoebas there will always be amoebas, and there is no reason to believe de-evolution is not occuring at the same time as evolution... Kids in a class room resemble Amoeba in a puddle of pond water, and I cannot believe it is coincidence...
I see the words "nature" and "essence" as both carrying with them the same fundamental meaning. When people talk of nature in general, usually they are referring to the essential aspects of life. This is why I would't say that the evolution of nature, or this essence we speak of, is necessarily blind, especially to the species which nature consists of. To say that nature makes the choice for the species, to me at least, suggests that nature and the species are two separate existences. I would say it is more logical to say that they necessarily choose together, and if there are choices made that usually entails some sort of purpose, or else a theory of evolution which involves some sort of "natural selection" could not be possible.
De-evolution is a tricky concept for the very reason that evolution occurs purposefully. I don't really see a difference between de-evolution and evolution because all change that occurs is governed by the reasons for it. Even if a species may seem less advanced from what it evolved from, which I'm not sure is ever the case, it only seems that way from our perspective. Nature evolves how it evolves, and its purpose for evolution is to maximize survival within a given set of circumstances.