Distinguishing "design" from "natural" still seems rather problematic to
me. [God is equally involved in either; the difference as I am using them
is whether He entirely uses means such as natural law or if there is some
"intervention"]. Considering the wide range of objects around the lab
here, the only criterion I can find to distinguish all man-made from
natural objects is that the former are not found in nature. This won't
help us recognize design in nature.
Many complex molecular-scale structures exist that are unquestionably
natural. Fullerenes require 60 or more atoms to be in just the right
position relative to each other, yet they can be generated in soot. Clay
minerals likewise involve a precise configuration of numerous atoms and
form by ordinary, natural chemical processes.
Fitting a specified purpose is also a doubtful criterion. For making
bricks, or pottery, those clay minerals fit the purpose very well. Knowing
the properties of various kinds of clay and of the product after firing, I
can provide very detailed specifications as to the exact purpose.
I recently saw a note (probably a letter to Science or Nature) that
suggested that the search for extraterrestrial intelligence was probably
much more difficult than generally suggested, assuming our pattern of
signal broadcasting is typical. (This ignores the question of whether
enough TV or radio transmissions demonstrate intelligence rather than
stupidity.) The increased complexity of our signals makes them much harder
to distinguish from random noise. Although generating some random sequence
requires very few instructions, generating a specified random sequence
takes a maximal number of instructions for the length of the sequence.
Thus, unless you know what the encoding method is, a highly specified
complex sequence and a random one will be difficult to distinguish.
Calculation of probability is also problematic. For the evolution of life,
or the creation of the universe, we have only one sample. Statistics are
not very meaningful. Also, probability with regard to past events is
difficult, and the question needs carefully asked. The probability that
life developed as it did is one. The probability that it would have
developed similarly under similar circumstances is unknown, as is the
probability that similar circumstances would exist. Also unknown is the
range of options that would have yielded a similar result. As far as I
know, no two species are known to have identical rRNA sequences, yet in all
organisms from bacteria to us they do the same basic thing (translate mRNA
into protein). As long as the ancestral organism came up with some
functional version of this sequence, it would have been functional. The
range of options is quite large, though probably rather smaller than the
range of non-functional options. However, there may be entirely different
ways that organisms could have assembled enzymes, if this had not been the
one chosen. This increases the probability again, though also adding
another element of uncertainty in its calculation.