On the other hand, evolution is known to be true. That is the fact part of evolution. So the question of if evolution occurred has been settled, even if the question of how evolution occurred remains open to revision.
And this fact/theory distinction is not particular to evolution. Science is full of ideas that we all agree are true even if we don’t fully understand them. A favorite example is gravity, which physicists are still researching even though no one would doubt it is real. Evolutionists like to say that evolution is as much a fact as is gravity. Indeed, some have said that evolution is even more certain than gravity.
There is, however, an important difference between evolution and gravity. Gravity is a fact because we can observe it. Indeed we can feel it. Not so with evolution. Even evolutionists agree that the adaptation that we can observe is insufficient to explain the large-scale changes evolution needs.
So how do we know that evolution, and especially that large-scale part, is a fact? This is where evolution becomes metaphysical. For the past 350 years a number of theological and philosophical proofs have mandated the truth of evolution.
Evolution is commonly understood to be “just science” because its explanation is strictly mechanistic. But that is the theory part of evolution. The fact part of evolution is metaphysical. Here is an example.
In his book Why Evolution is True, Jerry Coyne explains why embryology proves evolution to be true. It is not that evolution predicted precisely what we observe in the developmental stages of the various species. In fact, evolution does not require what we observe to be true. Evolution could explain a wide variety of observables.
But as Coyne explains, what we observe cannot be explained by alternative, non mechanistic, theories. As Coyne reminds his reader, the facts of embryology “make sense only in light of evolution.” This is equivalent to an IF-AND-ONLY-IF-THEN statement, and it reveals the non scientific, metaphysical, aspect of evolution. Coyne writes:
Embryonic stages don't look like the adult forms of their ancestors, as Haeckel claimed, but like the embryonic forms of ancestors. Human fetuses, for example, never resemble adult fish or reptiles, but in certain ways they do resemble embryonic fish and reptiles. Also, the recapitulation is neither strict nor inevitable: not every feature of an ancestor’s embryo appears in its descendants, nor do all stages of development unfold in a strict evolutionary order. Further, some species, like plants, have dispensed with nearly all traces of their ancestry during development. … Yet we shouldn’t throw out the baby with the bathwater. Embryos still show a form of recapitulation: features that arose earlier in evolution often appear earlier in development. And this makes sense only if species have an evolutionary history.
Now, we’re not absolutely sure why some species retain much of their evolutionary history during development. The “adding new stuff onto old” principle is just a hypothesis—and explanation for the facts of embryology. It’s hard to prove that it was easier for a developmental program to evolve one way rather than another. But the facts of embryology remain, and make sense only in light of evolution. [78-9]
Skeptics argue this is bad science and evolutionists retort that it is good science. But in fact, it is not science at all. Coyne and the evolutionists rely on metaphysical premises to make this argument. Evolutionists say their idea is a fact, and their proofs are always metaphysical.