> >>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).
I don't see how the question of common ancestry or homology is
related to Behe's notion of systems being impossible to evolve
gradually. And "indirect routes" seems such a broad category of
mechanisms, I don't see how it can be discounted.
I have no problem contemplating 'sudden hot-swapping' of complex
components in the mysterious early formative phases of terrestrial
evolution, such as the Precambrian. Nowadays we hear about genes
being artificially 'transplanted' among disparate organisms. Why
couldn't such things occur back when ecosystems were immature and
(natural) experimentation was rife? 'Early experimentation, later
standardization'.
-- Cliff Lundberg ~ San Francisco ~ cliff@noevalley.com