In order for a hypothesis to be considered a sound scientific theory it has to satisfy several criteria. Perhaps the most important of those is that scientists must be able to make testable predictions based upon the hypothesis. That is, if we assume the hypothesis is true, what sorts of consequences might we expect to occur and what sorts of experiments can we conduct to test whether those predictions hold true?
The central, foundational prediction of Darwinian evolution is that if all living things, especially those with complex genetic codes, evolved over billions of years from an original primordial cell with very simple genetic codes then the genetic material, DNA, must have a virtually unlimited capacity for variation. Otherwise, how did a simple genome in a primitive cell give rise to the highly complex genome in a mammalian cell?
Yet, according to geneticist and philosopher Kirk Durston in the 15 minute video below, every time this key prediction is put to the test, it's found to fail. Despite the ability of researchers to accelerate evolution in the lab and to simulate natural selection, every attempt to confirm this foundational prediction of Darwinism has hit a wall beyond which variation results in the death of the organism.
Durston asserts that such failures have made Neo-Darwinian evolution the most falsified theory in the history of science that still maintains a grip on the allegiance of a majority of scientists. He also explains why, in his opinion, this state of affairs exists.
A second prediction that follows if Darwinism is true is that the genetic information encoded in the cells of living organisms must have started at near-zero and increased until it reached the present state of affairs in which there are entire libraries of information contained in the nucleus of every cell in the body of every "advanced" organism. Durston points out, however, that this prediction is completely at odds with what we actually see happening in the world.
To the extent that there's variation within a taxon of organisms, it's due, as Michael Behe points out in his book Darwin Devolves, to a kind of devolution, a breaking of genes and an actual reduction of information.
Durston goes into more detail in the video, and all of what he says is easy for the non-biologist to understand. At the end he hints at several fascinating questions that arise from what has gone before:
If evolutionary variation is in fact due to a loss of information then doesn't that mean that originally there wasn't near-zero information present in the biosphere but rather a vast amount of information that has subsequently suffered degradation to one extent or another? And if there was a vast amount of information present at the very beginning of life, where did it come from and how did it get there?
These are intriguing questions for which naturalism has no plausible answer.