I've often heard by many that if all life on Earth was created by some entity, and not the true origin of everything, then that's just passing things down and so they outright reject any sort of intelligent design and either there is evidence that EVERYTHING was created by the ultimate entity or everything was spontaneous.
If such was the thinking with evolution, then there would have been no chain to follow. Either everything went directly from a single cell to what they are now or that's just passing things down too.
You can't deny that we may have been created by something else that also had it's origin elsewhere. You must go down the chain where ever it leads if you ever hope to learn the truth. By dismissing those possibilities means evidence isn't even being looked at or considered, it may be right under our eyes. Let's say were were created by other biological lifeforms, then could even be evidence on Earth or traces of them having been here we'll never figure out because it's not even considered a possibility to begin with, etc.