Modern studies of DNA have shown that it is entirely consistent with a common descent for almost all life on earth, a prediction of evolutionary theory made before we even knew about genes and DNA. If every major “kind” of animal was a unique creation, why should this be? Why should humans share genetic material with earthworms? Oh, I know, I know, God’s ways are mysterious and beyond our understanding, and He could do things whatever way he desired. But that’s the kind of hand-waving explanation that can be used to explain away anything.
How about we're all carbon based life forms living in the same environment, breathing the same air, drinking the same water, eating each other?
If DNA controls certain functions and describes certain physical characteristics, then it would make sense to use it in all species, much like certain code is used in computer programming. You don't make up new code for each program, you can use the same basic code and rearrange it to make it do what you wish.
It also makes sense that if organisms devour each other, they need to be similar enough so that the components can be metabolized. What good would it be if everything was so different that nothing could eat each other, but might even be poisonous?
Every kind of creature being a unique creation in that is was created and not evolved does not preclude using the same materials and code (DNA).
Uh, because they are all made from the same "stuff"?
What differentiates man from animal is the thinking, reasoning, rational soul, not the body. Both animals and humans have physical existence, so it is quite reasonable to surmise that a Creator would make both of them using the same genetic materials.