This is my first post here so excuse me if I'm in the wrong place or proposing a topic that's already been beaten to death by others.
All (or most) living things share the same genetic apparatus & codes, such as RNA, DNA, chromosomes, ribosomes, amino acids, genetic enzymes, etc. Examples of slightly different genetic codes exist but there are a number of possible explanations for their existence, none of which invoke the agency of the supernatural.
All (or most) living things share the same metabolic systems, with some explanable variations. For example, organisms exist with 'reverse Krebs cycles' as compared to most creatures have 'forward' Krebs cycles.
The natural origin of life not only cannot be dismissed, it may have likely happened several times, with some lines dying out while others served to exchange genetic information with the one(s) that did survive before dying out. Evolution via natural selection has functioned from the earliest times.
My thesis is as follows: the common nature of these aspects of life on a molecular level is very strong evidence that they only originated once & evolved as life did. We do not see the existence of entirely dissimilar genetic or metabolic systems that would illustrate entirely separate origins.
Let me leave my argument here & see where it goes.
Edited by John Sullivan, : Revise grammar