The possibility of powerful civilizations or entities cloaking
themselves in more innocuous biology is also an SF classic, handled
with sophistication in Greg Bear's "Anvil of Stars". It's doubtful that
a very small, very unobtrusive probe could do more than find the sort of
showy activities that might be detected from some distance.
Life is of course a species of nanotech. Nanotech suggests the
possibility of technological sophistication. How can 'natural'
nanomachines be distinguished from 'artificial' with a high degree of
certainty? It would be nice if as the scene from 'Blade Runner' the
fakes came with serial numbers. Rather like the 'gray goo' problem it's
not much of a problem if you're asking about 'accidents'. With no
consideration of possible deception, the difference is significant.
Deception, however, is a common aspect of all models of evolution. This
thread implies a transcendentally sophisticated tangle of deception. So
'how can you tell if life is natural?' is a messy question.
One direction that this line leads is an SF variant I don't recall
seeing (but I haven't kept up with SF). A post-singularity civilization
finds a planet with a complicated biosphere. They are very wary, to the
point of paranoia, about exploring directly. How can they tell who or
what might have made this place and with what purpose? The problem is an
exercise in applied theology - specifically a rigorous variant of the
argument from design. How can they evaluate the place while keeping
'deniability'? Maybe conspiratorially manipulating lesser species?
Anyway, the problem with the low profile line of argument IMHO is that
while it's fun it ends up in the same pattern of reasoning as conspiracy
theories. Occam's razor is the better tool.
Mark H. I'm just starting to do mail on netscape 3.0 and I haven't done
a signature file yet. I'm very happy with it so far for news/mail/telnet
the works.