>But you know? The big complaint from the anti-evolutionists is that a
>feather can't be useful if it is half evolved. Yet when one shows and
>example of a half-evolved feather that is very useful, you say that because
>it is useful it isn't half evolved. Which way do we want to play this today?
I don't want to play the old game of forcing all the known animals into a
simple-to-complex evolutionary series, where we assume that the horizontal
classificatory arrangement can be rotated to form the vertical evolutionary
sequence.
Let's get clear on what we don't know. How do you back up the claim that
a given structure is a transitional form? You can see that form B is
intermediate in structure between form A and form C, but what else do
you know? How do you know forms A, B, and C aren't independently evolved
from form X? Is an intermediate necessarily transitional? If it is
transitional,
how do you know in what direction the transition is proceeding? Do you
have fossil series showing change over time among unquestionably related
organisms, as in the eohippus>equus series? No, you don't.
>Which is clearly untrue given the elongated, feather-like scales of
>longisquama.
The tree of life is more like the creationistic candelabra of long lines
evolving vertically and independently, than like the ever-branching
Darwinian bush. I'd rather think about the origin of the candelabra
than look for transitional forms that aren't there. Personally I favor
feathers evolving from complex spines, and I'd guess 'feather-like
scales' evolved from the same structure feathers evolved from.
>You are correct about lungfish but incorrect about Ichthyostega, one of the
>transitional animals in the sequence leading to amphibians. His legs were
>only good for working like paddles. They could not support the weight of
>the animal. Yet they were quite armlike in other aspects of their mophology.
I take seriously the principle of reduction and specialization of skeletal
segments.
I'd be okay with Ichthyostega as the ancestor of all terrestrial quadrupeds, if
this
animal had enough bones in the digits to evolve into primates, for example,
through
a process of reduction. But it doesn't. Ichthyostega was evidently a quite
successful
form, well-adapted to its niche, judging from the number of fossils.
Intermediate, yes.
Related to lungfish, yes, but more likely a cousin than a direct descendant.
Transitional? Possibly it's an ancestor of certain other quadrupeds; we just
don't
know. Only the rigorous application of the gradual simple-to-complex paradigm
gives
Ichthyostega an exalted evolutionary status.
>>Pinnipeds have lost much of their limb structure; do you think that if
>>they were gradually forced to abandon the sea they would get that limb
>>structure back?
>Dollo's Law seems to preclude this. It is the observation that a structure
>once lost is never regained.
How do you reconcile Dollo's factual generalization with your belief that
skeletally
elaborative gradual evolution occurs? If a species needed (so to speak) to
re-evolve
a lost structure, why couldn't it? Wouldn't some residual embryonic
canalization
facilitate such re-evolution? The pattern of reduction explains the inability
to
re-evolve a structure. When the parts are gone, they're gone for good. Of
course,
functional equivalents of a structure can evolve by means other than skeletal
elaboration, that is, through distortion of the remaining parts.
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com