In Article <01bc0db5$a0ec1780$1578a3ce at default>, "Sarah at teleport.com"
<lfitz at teleport.com> wrote:
>Biologist used to say that "ontogeny recapitulates phylogeny" an
>invertebrate taxonomist that I know says "no more" . But I don't know why.
Because it isn't true.
>Ontogeny being the stages in embryonic development and phylogeny the
>stages in evolutionary development. For instance: a developing embryo
>resembles a fish at one point because it has gill slits and at another
>stage an amphibian, both susposed stages in the evolutionary development
A mammalian embryo is never a fish, although a fish embryo is more similar
(structurally) to a mammalian embryo than an adult fish is to a mammal. The
formulation that I like best is that ontogeny recapitulates the phylogeny of
ontogeny. My reading of this is that the embryonic development of different
species represents the branhcing nature of evolution, rather than an
"evolutionary developmental chain".
For a detailed, scholarly, but somewhat dense discussion of this issue, I
suggest Gould's "Phylogeny and Ontogeny". Although people may have
disagreements with some conclusions, this certainly provides a good
framework for thinking about the issues and plenty of references for you to
get into the background.
Department of Biological Sciences
University of Alberta
Edmonton, Alberta T6G 2E9
wgallin at gpu.srv.ualberta.ca