The Free Dictionary defines metaphysics as "a priori speculation upon questions that are unanswerable to scientific observation, analysis, or experiment" and Merriam-Webster as "the part of philosophy that is concerned with the basic causes and nature of things". Metaphysics is part of philosophy. Evolution theory is literally full of metaphysics. The philosophical foundations of evolution theory are naturalism and uniformitarianism. Evolutionists use similarities and differences in support of their belief while in reality they don't prove anything because they might just as well be used in support of common design.

Questions concerning the origins of the universe or life are part of philosophy. Darwin called the origin of species the "mystery of mysteries" in his book On the Origin of Species which, by the way, said nothing about the origin of species. He observed variety within a species and presented an unobservable and speculative theory about how one species supposedly turned into a completely different one.

Homology is central to evolution theory. According to evolutionists similarities and differences supposedly show a relationship between different and unique life forms. The reason why metaphysics is used to support that belief is of course that science can not possibly offer evidence for a relation between two unique and different life forms. The preconceived belief in common ancestry and macroevolution makes evolutionists interpret similarities in DNA or physical appearance of unique life forms as evidence for that belief. Unfortunately for evolutionists similarities and differences do not necessarily support common ancestry. It all depends on one's worldview. See also illusory correlation and third-cause fallacy.

Similarity can equally result from modifications to a common design. In observable reality we have countless examples of common design. Practically all cars show similarities like wheels, engine, brakes, body, etcetera. They appeared one after another in time. Modern cars are more complex and improved compared to older cars. Some cars may even be close to identical. But not one car ever evolved into another. They were of course all designed and created by intelligent agents. This goes for everything ever created by intelligent human beings. Nothing like that ever popped into existence naturally. Things left to nature will eventually decay or deteriorate. The natural world is subject to universal laws like entropy which dictate that nothing in the natural world goes from an inferior state to a superior state naturally. Not one real world example can be given for the idea that some complex functional entity changes into another at least equally functional entity without the intervention of an intelligent agent. Any mentally sane person simply knows that such things don't happen. Similarly to how connoisseurs work in the world of art, the fossil record can be interpreted according to the perspective of common design by the same designer.

Of course what goes for physical appearance also goes for genetics because DNA is related to physical appearance. The similarity in DNA between humans and chimpanzees is believed to be between 95% and 98.5% depending on what and how it is compared. About 90% of human genes have a matching version in cats. About 80% of human genes have a match in cows. And, about 80% of human genes have a match in mice. Cats have 82% of homologous genes with dogs. Cats look much more like dogs than any of these look like humans. So it simply doesn't seem to make much sense to compare apples and oranges. Similarities are nice, but explaining the differences and how they came about is what it's all about. Like for example orphan genes. For this evolutionists only offer fantastic and childish just-so stories and scientists can't offer any evidence. Hence metaphysics.

Are you half a banana? Or 98% chimp? Even if the software code for Microsoft Windows 10 were to be 95% similar to that of Windows 8, it wouldn't show any relation between the two. The reality is that they were both intelligently designed by clever people at Microsoft. The reality is that humans are not 50% bananas or 98% chimps. Physically chimps look more like humans than bananas so it would be expected that chimp DNA is more similar to that of humans than to that of bananas. But this doesn't prove anything about their origins. On top of that evolutionists erroneously believe and say that 98% of our DNA is useless junk. This was also a wrong prediction based on their belief in common ancestry. And if they really believe that 98% of our DNA were "useless" then it's the other 2% of "useful" DNA that's important and should be compared and explained. What evolutionists do in this regard is an example of cherry picking. Fact remains that each life form is unique and humans even more so because of their far superior mental capability. Each kind only produces offspring of the same kind. That some people lose sight of the most important facts of science has to do with blind faith and paradigm paralysis.