Xref: utzoo sci.bio:5127 talk.origins:15621
Newsgroups: sci.bio,talk.origins
Path: utzoo!utgpu!lamoran
From: lamoran@gpu.utcs.utoronto.ca (L.A. Moran)
Subject: Coelacanth and evolution
Message-ID: <1991Jun7.181909.28744@gpu.utcs.utoronto.ca>
Organization: UTCS Public Access
Date: Fri, 7 Jun 1991 18:19:09 GMT


Several people, including me, pointed out that coelacanths are not "living 
fossils" and that all organisms evolve even though there may be little
obvious change in external morphology.

Arlin Stoltzfus doesn't seem to like these ideas very much since he says,

     "Previous respondents have made rigid statements, and I hope they 
      haven't discouraged you. As several people have pointed out, it is
      a bit odd to speak of a "living fossil," and it is quite true that
      all extant species are "modern" in the sense of living in the present
      and being the product of the last 4.6 billion years of evolution.  
      However, the respondents misunderstand the word "primitive."  Also,
      to insist that there is no such thing as a living fossil and that all
      organisms evolve at the molecular level is to miss the point, since
      it does absolutely nothing to explain why the coelocanth (if that is
      how one spells it-- I forget) and other primitive species have 
      undergone less apparent morphological change than one might expect."

I hope that I understand what Arlin is trying to say here. Apparently he 
agrees that the term "living fossil" is incorrect and should not be used. 
I assume that he agrees with the main point of this thread which was a 
response to the question "Can organisms stop evolving for 400 million years?"
The answer is NO, do you agree Arlin?

Arlin is raising a second but related point, namely why do some organisms have
an exteranl morphology that is similar to that of extinct organisms.

In his opening paragraph Arlin uses the term "primitive species", but then he 
goes on to say,

     "Primitive" may be a value judgement sometimes-- when used in 
      reference to professional hockey, for example-- but in evolution 
      it can have a precise meaning, when used carefully. Any two species
      will have had a common ancestor at some time in the past: the species
      that is more similar to the ancestor is more primitive, in the exact
      sense. Usually, it is misleading to talk about whole organisms-- much
      better to speak of component properties. The ancestor of humans and
      whales walked on land. The terrestrial habit of humans can thus be 
      considered primitive in comparison to the whale's marine habit. One 
      can think of E. coli (as opposed to H. sapiens) as primitive in that
      it is unicellular, however, many features of this bacterium are 
      probably not primitive. Thus, it is easy to use the word "primitive" 
      in an exact and objective way, provided that one actually knows
      something about the relevant ancestor (this is often difficult)."

Actually you demonstrate that it is NOT "easy" to use the word "primitive" in
an exact sense! If you are referring to characteristics then it is permissible
to point to a "primitive" characteristic as one which has been around for a
long time. For example, when comparing whales and humans it is OK to say that
functional limbs are "primitive" compared to the derived characteristic of
degenerate limbs. Where people usually err is in assuming that a single
characteristic defines an organism; as, for example, in stating that humans
are more primitive than whales. Arlin makes this very mistake when he says
that "the species that is more similar to the ancestor is more primitive".
(In fairness he then qualifies his statement - but he should never have said
it in the first place if he really understood the precise meaning of 
"primitive".) 

Arlin Stoltzfus then says,

     "The coelocanth looks alot like some 400 MY-old fossils, and that
      is why people can correctly call it primitive. To be precise, its 
      gross morphology is primitive:...."

Arlin, you are contradicting your own statements. It is NOT correct to call
a modern coelacanth a primitive organism. This is not a description of a 
characteristic. Please BE precise.

Arlin Stoltzfus also says,

     "The Port Jackson Shark is another morphologically primitive species:
      it has a morphology similar to that of some sharks from the 
      Carboniferous period (ca. 300 MYA)...."

It would be more correct, scientifically, to say that the external morphology
of this shark is a primitive characteristic. This way you make it clear that
you are only comparing one characteristic.

Arlin concludes with,

     "So . . . many respondents have corrected the way you stated your 
      question ("is it common for species to not evolve?") by pointing out,
      as I have, that every organism is expected to evolve at the molecular
      level, regardless of the rate of evolution at the morphological level.
      But this doesn't answer the intent of your question, does it?  Its 
      exciting to think of primitive organisms and to imagine that they are
      a window to an otherwise murky past: you want to know why the coelocanth
      appears to live the same way for 400 MY while other organisms diverge
      from their ancestors and quickly acquire new properties!"

The first part of this paragraph is correct but the second part is confusing.
Arlin, it may be exciting to think of "primitive organisms" but by your own
definition and mine they do not exist. It IS appropriate to refer to some
primitive characteristics of organisms. When you refer to the "rigid"
statements that were made you were actually referring to rigorous statements.
There is a difference, especially in science.

-Larry Moran