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Re: recapitulation

>If I may step in on Ron's behalf here, it is accepted by modern
>evolutionary biologists that ontogeny can recapitulate phylogeny but it
>doesn't necessarily have too. Some good books written by eminant
>scientists on this subject are:
>Gould, S. J. 1977. Ontogeny and Phylogeny. Harvard University Press:
>Cambridge, Mass.
>McKinney, M. L. & McNamara, K. J. 1991 Heterochrony.The evolution of
>ontogeny. Plenum Press: New York.

As an addendum to Adam's post, there's something quite relevant to current
dinosaur work about this.  The work published by Burke and Feduccia arguing
that living birds preserve digits 2-3-4 in the hand, unlike the nonavian
theropod 1-2-3 pattern, relies heavily on ontogenetic constancy.  At no
point in avian development are more than four fingers present in the hand,
and in the absence of other data these could be 1-2-3-4 or, as argued by
Burke and Feduccia, 2-3-4-5.  Their assertion that it's 2-3-4-5 stems from
serial homology - the appearance of digits in the avian foot is 4-3-2-1,
and it ought to be the same in the hand - and the fact that the order of
appearance is 4-3-2-1-5 in most (but not all) nonavian tetrapods.

The problem with these arguments is that, as Adam and the references he
posted point out, ontogeny evolves.  If we accept a definition of
"ontogeny" to include all changes in an organism's lifetime from conception
to death, *any* evolutionary change could be regarded as a heterochronic
feature.  And not all evolutionary changes are expressed at the terminals
of ontogeny.

Around 1980, it was common for systematists to use ontogeny to polarize
character states in a phylogenetic analysis.  This is rarely done today,
largely thanks to a series of papers showing not only that stages can be
inserted, but that segments of developmental sequences can be up-ended.
This is why I find Burke and Feduccia's arguments so unconvincing - we know
early stages of development can be heavily modified during phylogeny, and
as such the embryological evidence they provide are, by themselves,
ambiguous.  (In the light of phylogeny, this ambiguity is lifted.)

Some of the more important papers on the dangers of overreliance on
ontogenetic criteria for polarity or homology:

Mabee, P.M.  1993.  Phylogenetic interpretation of ontogenetic change:
sorting out the actual and artefactual in an empirical case study of
centrarchid fishes.  Zoological Journal of the Linnean Society, 107:175-291.

Mabee, P.M.  1989.  An empirical rejection of the ontogenetic polarity
criterion.  Cladistics, 5:409-416.

Mabee, P.M.  1996.  Reassessing the ontogenetic criterion:  A response to
Patterson.  Cladistics, 12:169-176. (You should also read Patterson's
article preceding this one, which disagrees with it.)

de Queiroz, K. 1985.  The ontogenetic method for determining character
polarity and its relevance to phylogenetic systematics.  Systematic
Zoology, 34(3):280-299.

Rieppel, O.  Fundamentals of Comparative Biology.  (Much of my library is
not accessable at the moment - I don't have the full ref.  It's a book.)

The recent *Homology* volume also has some excellent references.


Christopher Brochu

***in transit***