When you want to compare and discuss evolutionary paths between two systems, say F and S, there are at least three main paths to consider:
- F evolved from S
- S evolved from F
- F and S share a common ancestor, A’
And for the last case, one should also consider that at the separation point, A’ will give S’ and F’, which will continue to evolve, giving respectively S and F. And A’ may itself evolve to give A.
Let’s say that F is the Bacterial Flagellum and S the Secretory System III. Considering only options 1 and 2 is an incomplete approach and lead to sterile discussions, where darwinists postulate that F evolved from S and designists that S should be ulterior of F, as it serves a function necessitating the presence of eucaryotes.
Let’s see how the third option may be presented:
A’ and A may or not exist today.
Both S’ and F’ may have evolve to give more then one system, I only represent one for each. At least for F which represents flagella we do know that several variants exist.
In this hypothesis S and F will share similarities, may even have homologous parts, but they aren’t on the same evolutionary line and there is no chance for one to prove ascendance.