I wrote:
>>What exactly does "common descent" mean in the context of having whole
>>chunks of complex biochemical systems being suddenly hot-swapped into new
>>organisms? Clearly many components of organisms can't have gotten there
>>by common descent is that's the case.
You asked:
>What are these instances of homology or similarity in biochemistry
>that can't be due to common ancestry?
Examples may include the blood clotting cascade, the immune system
and the prokaryotic flagellum, if one is to believe Michael Behe.
Based on his scheme, if such systems couldn't have arisen by gradual
events or by indirect routes then they'd have to have been assembled
de novo through something akin to Extranatural Assembly (EA). Would
these EA systems thus have to maintain much similarity to components
that previously existed in some direct ancestor? Certainly not, and
we do have many examples where the absence of common descent is
visibly reflected in the sequences we see. Of course, the examples
of which I'm thinking are horizontally transferred genes (and
organelles). These may not be EA-systems (I'd think not), but
there is really no reason to expect that EA would not produce similar
patterns.
So now we've got some EA proponents, who seem to delight in posting
articles such as "homology: ripe for burning", and yet seem to
embrace progressive creationism and common descent. It's as
if some people do not want to outwardly acknowledge something such
as homology because it smells too much like evolution, yet accept
AE-common descent/progressive creationism, essentially because of
the nested similarities (aka homologies) they see. However, it
seems that EA would possibly (?likely?), generate systems whose
patterns would be difficult to recognize as homologous to other
sequences. The fact that this usually isn't the case places a
large explanatory burden on EA proponents who also believe in
common descent (IMHO).
Elliott Sober mentions that one major difficulty confronting
creationist theories is the problem in finding and defending the
"auxiliary hypotheses" required to provide these theories with the
ability to make distinguishable and discernable predictions. The
homology-through-EA dilemma is one such example where the auxiliary
hypothesis needed to explain a phenomenon are lacking.
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com (despam address before use)