Skeptical1  wrote:

> wilkins{at}wehi.edu.au (John Wilkins) wrote...
> 
> > I think Haeckel is an atavism; at best his contributions were in the
> > arena of phylogeny (and that is corrupted by his misuse of illustrations
> > of embryos and his "biogenetic law"), and he does not
show that he fully
> > comprehends the mechanisms of Darwinian evolution, unlike, say, Moritz
> > Wagner, who manages to revise Darwin's ideas in a Darwinian fashion.
> 
> It would be quite interesting to trace the history of Haeckel's 1874
> diagram of vertebrate embryonic development. This has continued in use
> throughout the 1990s, though more usually as an illustration of Von
> Baer's ideas. Is this the most frequently reproduced diagram in the
> history of biology or what?

Indeed. It was only dropped from Albert's et al.'s Molecular Biology of
the Cell in the most recent edition. But these things go in cycles. For
a long time the most common diagram was either the one from Romanes'
_Darwin and After Darwin_ of the homologous wings of a bat, a bird and a
pterodactyl, or the ED Cope diagram of horse evolution with the hooves
gradually (and erroneously, as it turned out) developing into a single
toed hoof in a nice linear series. Some of Dobzhansky's and Simpson's
diagrams are eternally recurrent.
> 
> Also, would you not say that the current fascination with Hox and
> other genes represents a *kind* of reverting to "ontogeny
> recapitulates phylogeny", albeit at a molecular and not at a
> morphological level? Yes I know that sounds astonishing but I want
> people to think about the recent history of these disciplines.

Genes do pretty much the same thing in evolution that other
morphological traits do (yes, I said *other* - genes are treated as if
they were morphological characters in most phylogenetic analyses) - they
revert, occur through parallelism and convergence, and get compressed
deleted and inverted in the developmental sequences of evolving
lineages. I do not think that the biogenetic law can be revived for
genes, and for exactly the same reasons it failed for phenotypical
traits. Evolution is not a strong conserver of form.

Attempts have been made to reconstruct the ancestral sequences of
extinct organisms from a kind of "average" (technically, I believe they
are called "minimum message length" sequences) of their descendents, but
evolution is not always parsimonious. I am willing to be convinced
otherwise, of course, by Joe.
> 
> The generations after 1930 saw the triumph of comparative anatomy not
> only over morphology as a discipline, but also over an increasingly
> sidelined and timidly descriptive embryology (Conklin's "lawless
> science"). However the new developmental biology is not at all so
> timid. That is not to say that people will go back to Haeckel's law -
> clearly it is wrong as stated - but rather that there should be
> somewhat more sympathy for the *impetus* behind it. Why else is
> everyone suddenly so interested in "model system" zebrafish embryos
> and the like?
> 
> Just a generation ago "lawless embryologists" would have told us that
> zebrafish embryos are only of interest to students of zebrafish. That
> differs somewhat from the claims made for such studies today, does it
> not?

A generation ago, people knew that genetic sequences of Drosophila
taught us a lot about how genes behave in all organisms. Why would a
vertebrate genome be of less value? I think that what makes zebrafish
interesting is that their embryos are transparent, apart from their
intrinsic value, not their comparative anatomical similarity as such.
> 
> Harry (Skeptical1)


-- 
John Wilkins
B'dies, Brutius
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