What you are trying to call “devolution” is actually evolution. But I’m a little confused-- you do believe in genetic change of a species over time. Obviously, if two populations are separated (like in different islands) don’t you think that would affect the way in which they “not really devolved”?
Devolution is the process of degradation of the genome which results in serious medical conditions and even death of the unborn. There are built-in protective mechanisms against this including genomic transfer and repair, sexual reproduction which allows for functional back-up copies of genes and would include natural selection as means to prevent malformations to continue. It assumes that there was once a better suited organism whose progeny experienced the random chemical changes that occur as a result of simple noise in the system, the glitches that occur even when there is 0.999 reproducibility, the effect of viruses, radiation and toxins.
I see a problem arising in the identification of the raw data with the story of evolution. Let’s assume the data, which is actually biased by the theory that defines it, is more or less correct; it can like tiles in a mosaic, be organized in such a manner that presents a very different picture than that of Darwinism.
There are many causes behind genetic modification in successive generations. There are transformations even in one life time as the NASA Twin Study demonstrated, revealing that changes occurred in astronaut Scott Kelly’s genes during his year in space, and two years later 7% did not return to baseline. The study compares what happened to Kelly with his identical twin, Mark, who remained on Earth.
It speaks to the fact that all cellular components are linked and interact, that DNA is not some transcendent cause but rather part of an integrated system, which ultimately involves a creature. And, that creature is a whole, a unity of being consisting of what we might differentiate as physiological and psychological dimensions within an encompassing reality that is its existence as itself and as an expression of its kind. The original creature, the first of its kind was created, containing the potential for diversity that we see in the world, some of it planned, some a mistake, the result of random mutations.