[steve-b]

complex chemical processes that don't provide any benefit if even a single component isn't present would be unlikely to develop as a gradual process

This turns out not to be the case.

[Question_Assumptions]

This turns out not to be the case.

It turns out to not be the case depending on your assumptions. Apply the same argument to SETI. Finding a narrow band transmission, for example, does not prove that it can't have a natural explanation. In both cases, if you pre-suppose that (A) an intelligent source does not exist and (B) that there is always a natural explanation, even if we haven't found it yet, then no electromagnetic signal of the sort being looked for will prove anything.