>WRT to Glenn's discussion of the number of different sequences that will
>produce a given fold.
>
>Mutagenesis studies on proteins of the past 15 years has shown that they
>are amazingly resilient to many different substitutions. (This happens to
>be my own area of biochemical research. I study the effect of changing the
>sequence on changing the fold or structure of the protein.) We and others
>doing this sort of research find that for many (if not most) positions you
>can substitute several different amino acids in that given position. In
>many cases you can substitute every amino acid in particular position. Of
>the mutants that have been studied nearly all of them are still functional
>in addition to folded because function is selected for or assayed for. Bob
>Sauer's group at MIT have systematically substituted every amino acid into
>every position into the ~100 residue lambda repressor. They conclude that
>there are 10^55 (yes, that's fifty-fifth) different sequences that produce
>the functional lambda repressor fold (Reidhaar-Olson and Sauer). The
>results of the Brian Matthews lab, our lab and others with T4 lysozyme is
>similar.
>
These results are similar to those Yockey gives for iso-1-cytochrome c.
He considers the same types of things you mention above and calculates
that there are 2.316x(10)^93 functional sequences for iso-1-cytochrome c
out of 1.15x(10)^137 possible sequences. The probability of selecting *any*
of the 2.316x(10)^93 functional sequences is thus 2.0x(10)^-44.
T Gray:=================
>Interestingly, I've seen at least one creationist turn this argument around
>now and say that even if there is 10^55 possible sequences that's still
>only one in 10^65 of the possible 10^110 sequences. I reject this argument
>as being a problem because it assumes that functional protein sequences are
>assembled by random processes which they are not and it denies the efficacy
>of selection.
I have been trying to think of the best way of responding to Glenn's musings
on probability. Before I actually go to the trouble of typing something in
it may be a good idea to get some clarification on what Glenn was proposing.
I believe that either I or Terry have misunderstood. I thought I "heard"
Glenn arguing that the multitude of different functional sequences possible
revived some hope for the possibility of constructing a protein purely by
chance. If this is indeed the proposal, then the creationists objection
mentioned above is entirely appropriate.
BTW, I do agree with what Terry has said above. The best answer to the
probability argument is to point out that it *does* assume a random
process. If a non-random process is proposed then the probability calculation
is no longer appropriate. That life arose by a random process is not, however,
a strawman invented by creationists. It was considered a viable explanation
only thirty years or so ago. The reason it isn't considered viable any longer
is due in large part to the probability calculations. Thus these calculations
have served an imporatant function in the direction of research on the origin
of life.
>On the whole I
>find the sorts of arguments made by Thaxton, Bradley and Olsen and others
>totally suspect given these results and with Glenn I agree that we are
>sadly misguided in our apologetic efforts when we use them. They might
>appear convincing to a lay audience, but they are filled with holes.
>
Let's recall the quote from Thaxton et al given a few days ago:
"Such improbabilities have led essentially all scientists who
work in the field to reject random, accidental assembly or fortuitous
good luck as an explanation for how life began." (Bradley & Thaxton,
p190)
This is exactly the point I was making above. There is nothing devious about
the probability calculation as long as it is made clear exactly which
scenario for the origin of life it addresses.
==
Brian Harper:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=
"I believe there are 15,747,724,136,275,002,577,605,653,961,181,555,468,
044,717,914,527,116,709,366,231,425,076,185,631,031,296 protons in the
Universe and the same number of electrons." Arthur Stanley Eddington
:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=:=