Darwin-L Message Log 4:21 (December 1993)

Academic Discussion on the History and Theory of the Historical Sciences

This is one message from the Archives of Darwin-L (1993–1997), a professional discussion group on the history and theory of the historical sciences.

Note: Additional publications on evolution and the historical sciences by the Darwin-L list owner are available on SSRN.

<4:21>From mcglynn@cheshire.oxy.edu  Wed Dec  8 11:40:50 1993

From: mcglynn@cheshire.oxy.edu (Terrence Peter McGlynn)
Subject: extinction
To: darwin-l@ukanaix.cc.ukans.edu (Darwin-l mailing list)
Date: Wed, 8 Dec 93 9:42:27 PST

There is a definite analogy between linguistics and evolution regarding
the types of extinction.

In the formation of new species (this is really going somewhere), there
are two general types of events, called anagenesis and cladogenesis.
The latter is where a species "branches off" a currently existing species,
while former indicates such an evolutionary conversion of one species
over time.

In such a process of conversion, there is no well-understood rule to
delineate when a species changes from one to another, which would make
the first one extinct.  The definition of a biological species (which
always argued by many, but is the best model we have now) rests upon
reproductive isolation -- if an individual cannot reproduce with another,
for behavioral or physiological reasons, then they are not in the same

It makes a lot of sense at one moment in time, but when the factor of time is
involved, it's very confusing trying to determine what could or could not
reproduce with another organism.  I'm definitely not a paleontologist, but
it looks like fossilized organisms are called different species when there
is a significant enough structural change.  However, the type of
slow change from one species to another is probably much less common from
the "branching" evolution, because usually new species arise in very small
populations that are isolated from a larger one... this is getting very
biological.  In short, when did homo erectus become homo sapiens?  That's
probably an equivalent question to when did Latin become Spanish.

Terrence P. McGlynn      Associate Student of Biology
7925 Ellenbogen Street   Occidental College Biology Department (sort-of)
Sunland, CA  91040-2261  phone:(818)352-5242  internet: mcglynn@oxy.edu

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