You say we need evidence of design. On your view, is such evidence of design by non-humans even conceivable, or do you accept in-principle arguments that rule it out? A lot of times people say "Show me the evidence, and then, come to find out, they buy in on in-principle arguments that rule out those kinds of design inferences across the board. For example, if the galaxies in the Virgo Cluster were to spell out the words "Turn or burn, SmilidonsRetreat This Means You", there are arguments that lead to the conclusion that even if such a case, attributing that to God would be to commit the God of the Gaps fallacy. So, when you say "Show me the evidence," I would like to know if there is some possible evidence you might accept. See Lydia McGrew's discussion here.
Finally, you say, To consider design as an option, we need to know who did the designing? How? When? On what things?
No, I am afraid I don't buy that principle. Consider McGrew again.
It would be a very different matter if, far in the future, we managed to take pictures of the region around Alpha Centauri (where no humans had ever gone) and found incontrovertible evidence that a Volkswagen Beetle was orbiting a planet there. We might indeed wonder why anyone, particularly any non-human, would want to make that object just there. Nonetheless, the fact that the object would be virtually type identical to objects known to be made by agents, and the vanishingly small probability of its arising in any non-intentional fashion, would make it only reasonable to conclude that the car was designed by someone or other. The design claim in biology is best construed as saying something much like this: We have found complex biological machines. These machines, being in some cases part of the human body, or predating human life on earth, could not have been made by humans. But even if we do not know who designed such machines or why, it does not follow that we are incapable of telling that they were designed.