Board Thread:Suggestions forum/@comment-32918765-20171030193812/@comment-33185350-20171104220520

Ok you are right, the process of macroevolution could theoretically occur on Middle-Earth. However all creatures on Middle-Earth were created by the Valar, and then varied or became corrupted. Evolution was not the source of life on Middle-Earth.

But let’s take this a little further. Microevolution is a known phenomenon. Scientists have observed organisms adapting to their environment to survive. You are correct that microevolution can include mutation, but it still doesn’t add a significant amount of new information to a creature’s genome. It’s generally just adaptation according to information already in the genes. We know for certain adaptation occurs on Arda at least.

Macroevolution, on the other hand, is a theory. It has not been observed by scientists. It’s just one attempt at explaining the source of the diversity on earth. It is generally the scientific consensus, but it has not been observed and cannot be repeated in a lab. Its purpose is to explain life. On Arda, we know the Valar created life. There’s no need to try to explain it with evolution. Adaptation is present, but that does not mean macroevolution is. Macroevolution requires a huge amount of material added to a creature’s genome, such as the information for functional wings. Adaptation does not add information. So no matter how much adaptation occurs, it won’t cause macroevolution. We’ve selectively bred animals like dogs and successively achieved what one might call microevolution. But the dogs haven’t changed into something else. They haven’t evolved wings, or other advantages (in this case some mutation that makes them cuter? I don’t know). They aren’t progressing towards any higher form of life.

It really depends on how you interpret the fish passage. I see it as adaptation, you see it as evolution. We can’t really know for sure what Tolkien meant.