From: salem@pangea.Stanford.EDU (Bruce Salem)
Subject: Re: More on three and four chamber hearts
Organization: DSG, Stanford University
Date: 14 Apr 92 02:47:15 GMT

bk186@cleveland.Freenet.Edu (Julie Thomas) writes:


>In a previous article, salem@pangea.Stanford.EDU (Bruce Salem) says:

>Yes I did.  Thank you.  However, I did not find it to be all that
>helpful.  If I recall, you posted about the human heart developing
>from a "primitive"

	I don't recall using that term.

>structure into the four-chambered heart in a manner
>somewhat suggestive of the evolutionary procession.  But unless the
>null hypothesis would be that the heart should develop in a different
>manner, I fail to see how this is evidence of the supposed transformation.

	Do you have any evidence for an alternative?

	In the original posting mentioning problems with the
development of the four chambered heart from supposed two and three
chambered I said that because there was no fossil record on this 
that we would have to use developmental sequences as the clues.
Despite problems with the idea of recapitulation in ontogeny of
the phylogeny, the developmental anatomy is a clue to the phylogeny
if you are going to entertian the possibility of phylogeny. Do
you have an alternative to that?

>>That account (Arey, 1942 Developmental Anatomy pg. 316 ff)
>>sayes that the development proceeds in stages roughly analogous
>>with the enchancements from fish to mammalian form.

>Right.  "Roughly analogous".  That does not give me reason to suspect
>this must reflect some ancient phylogenetic transformation.  

	Again, what evidence do you have that some ancient phylogeny
is not reflected in the developmental stages? So, the developmental
sequences are not a simple reflection of phylogeny? I grant you
that, but are you going to go the rest of the way and assert that
the developmental sequences cannot replect phylogenetic steps or
that these stages decieve us in some fundemental way about phylogeny?
Or are you going to assert that there is no phylogeny, whatever
the developmental sequences?

> The heart
>>begins as a thichening in vascular structures in the crainial
>>area of the embryo, develops into a three chambered affair
>>with atruim, ventricle, and bulbus.

>Well, the fish heart consists of a four chambered affair in series.

	But there are three chambered hearts. What does a fish with
four chambers in series mean? What difference does it make that
there are three and four chambered hearts in series and two pairs
of parallel chambered in four chambered hearts?

> A forth and smaller segment,
>>the sinus venoosus, which developed out of a different structure
>>than the rest of the heart, unites with the right side of the
>>atrium.

>If this is true, then the fish heart is most different.  

	So? I didn't assert that the fish hearts, remember
these are modern Teliosts, are direct ancestores. Do you know
how the Placaderm heart was constructed? What about sharks?

> As the heart developes the atrial and ventricular partitions
>>begin to appear at the same time that the bulbus is absorbed by
>>the ventricle. Out of the bulbus both the aorta and pulmonary arteries
>>are formed, and this is not due to a partition of the atruim. At
>>this point the venous circulation enteres the atrium and the
>>arterial leaves from what used to be the bulbus. The heart is
>>still three chanbered. It is the transformation of the bulbular
>>region and ajoining parts of the right ventricle into the
>>right ventricle and the simutaneous fornation of the remaining
>>septa that results in the four chambered heart. The partitioning
>>occurs after the antrial and venous circulation have become
>>isolated at opposites ends of the heart. So the transformation
>>of the polmonary function predates in the development, at least,
>>the greater efficiency effected by partitioning and formation of
>>valves.

>How does this help the reptile to mammal heart transformation?
>Recall that in the reptile (with a three chambered heart) both
>atria enter into the left ventricle.  What you need is the two
>atria dumping into the left ventricle, then the right one shifting
>to the right as the intervenricular septum completes it's growth.
>The funny thing is that when it does, there remains an opening
>between atria.  

	Why? The original stipulation you made was how to
incorporate the pulmonary circulation while splitting the
ventricles. If the developemnt is to be taken as a guide,
it suggests that the pulmonery circulation may have been
established before the ventricle got split. The development
shows the that artium of the old three chambered plan becomes
the left atrium, and that the right atrium forms from the
bulbus and part of the ventricle in the arterial end of the
heart. The development of duel atria is well established and
takes place at the same time the ventricle is divided by its
septum.

>>	Now, I hasten to add that I an not making a case for
>>recapitulation, as Gould makes a good case that the relation
>>between development and phylogenetic steps is very much
>>more complicated than that.

>Covering the bases, eh?

	No, just seeing that the picture is more complex
than first thought. See Gould, "Ontegeny and Phylogeny",
the original idea of recapitulation is clearly wrong, but
the whole idea that ontegeny says something about
phylogeny is not dead, reality is just more complicated.

>  I have a great deal of difficulty accepting
>ontogeny as evidence for evolution when the cards are stacked so that
>similarities supposedly mean relationship and differences are assigned
>to some "special" category where ad hoc explanations reign.  The
>whole endeavor is set up so that only evidence for evolution can be
>found.  I reject this methodology.  If similarities count for,
>differences count against.  (of course, similarities might not count
>for and differences might not count against; subjective interpretations
>are everywhere!).

	Which is all fine, be a skeptic, say that people are
constructing "just so" stories, but the real proof of your
pudding is for you to offer something better. Find something
that fills in the voids that can be tested, that tells how
to look for new and decisive evidence, and then get it and
present it to us with your arguments. Until then you are
just a naysayer, and as many people are reacting to the
ideas behind evolution from emotion and bias, that unless
you can build something constructive with your objections,
you too are subject to the question of bias.

	If there were any other theory that delt with the relations
and differences between life-forms, other than evolution, for which
tests could be defined, then present it. Creationism does not meet
these criteria. What do you have in mind as an alternative to
Natural Selection or an alternative to inperpeting simularity
as phylogeny as evolutionary relatedness? Are you going to bring
in some evolutionary theory other than Natural Selection, or
a non-evolutionary idea? What idea is non-evolutionary which can
explain simularity? Are you just going to repeat Creation?
What do you have in mind? Remeber, it is not sufficient for
you to just say that a theory is incompletely proven, and is
wrong. What is your theory?

Bruce Salem

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