I think the real problem here is the heterogenous and malleable thing that is the ID movement. As we all know the 'aliens' argument is, for the vast majority of ID proponents, a fig leaf to allow them to pretend the ID isn't all about their religious convictions.
There is no logical reason why a complex organism could not previously have evolved which did not display
irreducible complexity. It is hard however to see how one could evolve which didn't have complex specified information in some form. The only example of life we know of is supposedly 'too complex to have evolved' , at least on Earth in the commonly accepted time frame, but that doesn't rule out the existence of other forms of life which are equivalently complex but not in such a way as for their evolution to have been as astronomically improbable as IDists hold ours to have been.
There are plenty of
ad hoc apologetics one can come up with as to how hypothetical complex aliens could have evolved
de novo but humans could not have. They could have had an earlier formed planet with a prebiotic atmosphere more conducive to abiogenesis which reached a suitable environmental state for life to develop billions of years before or own. Were we to have any actual 'Irreducibly Complex' system for which there was no plausible scaffoding pathway that might be similarly considered. In the absence of having to provide evidence it is possible to argue almost anything with such
ad hoc musings.
The problem is that outside of abiogenesis the aliens argument is no more of a useful hypothesis than the god one, considerably less so in fact. At least once one has gone as far as the god hypothesis one can allow all sorts of hidden supernatural tinkering in the genome, like Randman's quantum nudging jiggery pokery. With the aliens hypothesis, as with a front loading form of theistic ID, we are confronted by the fact that there is no evidence for any sort of encrypted or hidden pre-formed information in the genome.
So aliens might explain the supposed Irreducible Complexity of the bacterial flagellum or core conserved metabolic cycles, but unless you get into Eric Von Daniken territory with aliens actively zipping about in UFOs curating the planet for millions of years they won't get you to an 'Irreducibly Complex' vertebrate immune system.
As was pointed out even the most prominent ID figures don't seem to be able to agree on what the theory means. Its worse down at the ground level, such as here at EvC, where people who are just straight creationists and deny macroevolution and sometimes even the existence of beneficial mutations regularly call their position ID.
I know much of this has already been covered in this thread, but that doesn't usually stop me sticking my oar in.
TTFN,
WK
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