>The Boston Globe, May 30, 2000, Tuesday, Pg. E1
>HEADLINE: A LITTLE FISH CHALLENGES A GIANT OF SCIENCE
>BYLINE: By Fred Heeren, GLOBE CORRESPONDENT
This article struck me as very curious. I am quite familar with Chen's
work, in fact he visited the Univ. of Rochester while I was there working
on my doctorate. There is nothing in his published work, or its reception
by the paleontological community, that suggests that his work is percieved
as "nothing less than a challenge to the theory of evolution."
Several articles make the point that molecular data would predict that
chordates should appear in the record by the early Cambrian or earlier. It
was already known that vertebrates were present by the late Cambrian.
Furthermore, the expectation was that the common ancestor for the chordates
would be anatomically similar to the lancelet (Amphioxis). Haikouella does
appear to resemble the lancelot in many ways and for that reason was named
H.lanceolata.
In the articles describing this and other early Cambrian chordates there is
no suggestion that these discoveries pose any challenge to evolutionary
theory.
Following is a quote from the article describing Haikouella for which J-Y
Chen was the first author with D-Y Huang & C-W Li. "Although living
chordates display an amazing diversity of body forms, extant lancelets are
broadly accepted to be the best available proxies for the latest common
ancestor of the cephalochordates and craniates. Palaeontological
information on Yunnanozoon and Haikouella, as well and molecular genetic
data, have lent strong support to this concept. It is possible that all
the craniate body forms evolved from a common ancestor resembling these
fish-like species. Although it is commonly considered that the origin of
the craniates was signalled by the relatively simultaneous appearance of a
conspicuous brain and an endoskeleton including a cranium, our finding
indicates that the craniates originated through a set of separate events
over a long interval of time." (J-Y Chen, D-Y Huang & C-W Li, 1999, An
early Cambrian craniate-like chordate: Nature 402:518-522.)
In a review of other Chengjiang chordate discoveries, Philippe Janvier
wrote: "Shu et al. have analysed the phylogenetic position of these two
Canbrian fossils in the framework of previous analyses of vertebrate
phylogeny. Strangely, one of the two species seems to be more closely
related to lampreys than to any other vertebrate group, whereas the other
appears as the sister-group to all other vertebrates but hagfishes. ...
Nevertheless, the result makes broad sense, because it suggests that
lampreys and their fossil relatives had diverged already in the Cambrian,
as predicted by previous phylogenies." (Philippe Janvier, 1999, Catching
the first fish: Nature 402:21-22)
How these statements can be squared with the spin of the editorial are
beyond me. How can discoveries which are in accord with previous
expectation and with phylogenetic prediction suddenly be touted as "nothing
less than a challenge to the theory of evolution"? Curious!
Here are a few other relevant articles:
D-G Shu et al., 1999, Lower Cambrian vertebrates from south China: Nature
402:42-46.
J-Y Chen, et al., 1995, A possible Early Cambrian chordate: Nature 377: 720-722.
Carl Zimmer, 2000, In search of vertebrate origins: beyond brain and bone:
Science 287: 1576-1579.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.ksu.edu
http://www-personal.ksu.edu/~kbmill/
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