According to standard Darwinian evolutionary theory that's true. The selection and the generation of variation are separate steps.
Mutation, symbiosis, viral infection, sexual recombination, and so forth, provide the variation. Selection acts on that variation.
There is no "one single philosophy" involved.
Nobody "started with" any scientific theory, and Darwinian theory is especially difficult to grasp. Most people are adults before they have any real handle on Darwinian evolutionary theory. You, for example, don't understand it (that's why you have been ignoring the evidence presented to you).
You can't post a single accurate statement about any of the faiths or philosophies behind Darwinian evolutionary theory. You have no coherent or consistent idea of what "Naturalism" means, for example.
Inbreeding is not evolution - specifically, it is the name for one common cause of failure to produce necessary variation (implying a failure to evolve in Darwinian fashion).
As far as I know, nobody has nailed down "the" cause - or even the most important cause - of the extinction of the Woolly Mammoth. https://en.wikipedia.org/wiki/Mammoth. They did not suffer from inbreeding, for example, until their populations had somehow been reduced to a remnant. And most researchers seem to think that the explanation of the Woolly Mammoth's extinction probably should shed light on the near-simultaneous extinction of the other mammoth species extant at the time - don't you?
Meanwhile, the many examples of beings that did not go extinct for many millions of years are proof that extinction via corruption of the genetic code is not inevitable. That's a central problem with your bogus "genetic corruption" argument - even one counterexample can blow it up, and there are millions.
Define "environments".
Define "stable". Include the concepts of "winter" and "forest fire" and "drought" and "flood" and "invasive, extinct, plague, migration, or newly evolved species" within the scope of your definitions.
