From: colby@bu-bio.bu.edu (Chris Colby)
Newsgroups: talk.origins
Subject: response to Herb Sutter (I)
Date: 5 Sep 92 17:55:24 GMT
Distribution: talk
Organization: animal -- coelomate -- deuterostome

In article <1992Sep4.929.17251@dosgate> "herb sutter" <herb.sutter@canrem.com> writes:

>Please forgive my ignorance and go slowly, but do you base your evidence
>for common descent on structural and genetic similarity in living forms
>and in fossilised remains?  

Among other things, yes.

>I must say that I'm dubious of most such links
>I've seen so far, if only because similarity doesn't imply relation.

Will you grant that similarity is often a measure of relation in a
time scale we can witness? For example, if you had two dogs and
two cats (one male and female of each) and they had offspring --
do you think you could tell which animals had the puppy and which
had the kitten? Will you grant that similarity is at least consistent
with relation (even if it does not rule out other possibilities)?

Second, are you aware that biological traits are distributed in a
heirarchical fashion? Is this consistent with common descent?

>One of the reasons I'm dissatisfied with many such explanations:  It is an
>observed fact that many species are similar to other species.
>Evolutionary theory was developed to explain that fact by stating that one
>came for another or they shared a common ancestor.  Then, to prove the
>theory, it is said that the similarity between many species is proof that
>they must be related

Not quite, organisms were grouped together originally by examining
morphology. Similar species were said to be more closely related to
each other. And, more importantly, traits fell into heirarchical
patterns within phylogenies.

This generated further predictions that can (and have 
been tested). For example, if two species are more closely related
to each other than to a third species, gene sequences from them should
have less differences between them than between them and the third
organism. Evolutionary biology predicted that DNA sequences should
provide an independent measure of phylogeny prior to DNA sequencing
being available.

This prediction has been borne out. Almost every study using gene 
sequences has supported the traditional grouping of organisms established 
by morphologists. In a few cases, this was not so -- but, these cases
generally dealt with areas where there was substantial disagreement
over the taxonomy.

>I would be grateful for references.  If you mean fossil sequences (perhaps
>including creatures like Archaeopteryx (sp?)), I should warn again that
>I'm dubious of claims that similarity must imply relation.  Evolutionary
>theory cannot use similarity as proof, since that is what it is trying to
>explain.

Try reading "Vertebrate Palaeontology" by Michael Benton (1990, Unwin
Hyman, Boston). It has a brief discussion of this and references to
the primary literature. I have no training in paleo, but this seemed
to me to be a very informative book. 

I agree that the _same_ measure of similarity can be "recycled", but
independent measures (DNA sequencing, protien sequencing, embryological
studies and others) confirm phylogenies drawn by morphologists in
the vast majority of cases. In addition, patterns of biogeography
from the present and past (as seen through the fossil record)
support common ancestry.

Similarity is only one line of evidence leading to the inference of
evolution. Suites of traits arranged in heirarchical patterns is
another, better line of evidence. Notice that numerous independent
traits are used to strengthen the case. In addition, developmental
patterns in organisms support the case of evolution as does the
fossil record, not only by documenting transitions but (more im-
portantly, IHMO) in showing temporal and spatial biogeographic 
patterns consistent with the inference of common descent. Notice
that this is another _independent_ line of evidence (as is the
indepedent evidence of an ancient earth and even older universe).

>|UUCP:canrem!herb.sutter INTERNET:herb.sutter@canrem.com COMPUSERVE:70312,1233|

Chris Colby 	---	 email: colby@bu-bio.bu.edu	---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
 	--Kurt Vonnegut from "Galapagos"

Newsgroups: talk.origins