Are you talking about Darwin specifically and not evolutionary
> theory in general?
>
> As an example of a complex structure, how about the forearm?
> Which came first, the radius or the ulna?
An interesting question. Does anyone with a good knowlegde of
fossils know if one of these bones does in fact appear before
the other, or did they both appear simultaneously (as far as
we know)?
How could one of these
> bones evolve to complement the other? Which end would evolve
> first? How could the second bone appear as a useful part,
> attached at both ends, with all the associated muscles etc?
I have seen arguments against evolution, or at least against gradual
evolution, based on this sort of question - that such change would
not be possible because the statistical likelihood of bones, muscles,
nerves, blood supply etc etc all evolving at once and in the same
direction is very low.
If you only consider the fully formed animals, then this seems like
a good argument, but actually it is completely empty. Animals of course
do not produce their offspring fully formed in an instant, they
develop over a period of time from a single cell. Now I wouldnt
claim a great deal of knowledge about embryology, but as a former
medic (albeit a failed one!) I have read a bit about it (and it's
fascinating, I can asure you!) The differentiation of the original
cells into the different tissues which they eventually form involves
chemical inducers, and gradients of concentration of different
chemicals in different regions of the embryo. So one thing will
trigger the development of another, and all will end up correctly.
(The same way that people who have different heights don't have
a problem with their bones being too long for their muscles or
vice versa!
> For that matter, how could any new articulated bone evolve?
> Articulations are intrinsically discontinuities; the evolution
> of new articulations through insensible gradations is impossible.
I don't know about 'impossible' but you have a good point. Are there
any fossils which show partially formed joints?
>
> The evolutionary history of the skeleton of the forearm is easily
> traceable from the lungfish limb, when it consisted of many
> similar parts, to its present state, where the familiar process
> of reduction and specialization among parts has left the radius
> and ulna.
Perhaps you have just answered one of my questions above! I assume,
then, that the present arangement has come from an earlier one which had
more bones? I know this is the case in, eg the horse's hoof, but I
don't know anything about the precursors of the forearm - or indeed of
the upper arm. What were these bones before? just part of the structure
of fins? It seems a highly arbitrary (but teleologically highly useful)
arrangement merely to support a fin!
> There is a problem only if we insist on simple-to-complex
> gradual evolution. This is the basic error in all the arguments
> from 'irreducible complexity'. Evolution is not necessarily
> gradual, and it certainly does not inevitably proceed from the
> simple to the complex (in any sense of the word).
>
Gary