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evolution:phylogenesis as mirror of ontogenesis?

Keith Landa landak at marian.edu
Sat Feb 1 00:41:23 EST 1997

Sarah at teleport.com wrote:

> 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
> chain.

The problem is that it's not really accurate to say that a developing 
(mammalian) embryo resembles a fish at early stages of development.  It's 
more accurate to say that a mammalian embryo early in development resembles 
a fish embryo early in development.  This is more than a semantic 
difference and it relates to the other misconception in your posting, the 
"evolutionary development chain".  The great chain of being notion, along 
with ontology recapitulates phylogeny, lead to the idea that fish evolved 
into amphibians which evolved into reptiles which evolved into mammals 
which evolved into primates which evolved into humans.  This is not how 
evolution works.  The ancestors of modern fish and the ancestors of modern 
mammals diverged and went their separate ways several hundred million years 
ago, with each group branching independently (after divergence) into 
thousands of different species.

Keith Landa
Department of Biology
Marian College
Indianapolis, IN
landak at marian.edu

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