From: Joel Roth
To: All Msg #369, Sep-21-93 06:22AM
Subject: Repost: Evolution of three- and four-chambered hearts
Organization: Aegis Society, Kyoto Japan
From: jroth@aegis.or.jp (Joel Roth)
Message-ID: <4635@aegis.or.jp>
Newsgroups: talk.origins
Julie Thomas' critique of theories of heart evolution, posted about
one year ago, strike me as well written and referenced enough to merit
reposting.
She argues against, in her words, a 'just-so' scenario for evolution
of the heart that conceals what appear to her to be mortally
maladaptive transitional stages, and stages that differ dramatically
(in her opinion) from developmental sequences.
These articles underscore a major difficulty I have in accepting the
evolutionary hypothesis: I have not yet heard sufficient evidence to
believe that every step in the hypothetical development of biological
systems over time would have necessarily improved or maintained the
viability of the organism--which I understand is a precondition of
evolutionary scenarios based on selection or drift.
My experience is that macro-size systems that we see in the world
around us require substantial *investment* of energy, skill, and
material resources as a rule before any return is achieved. (A factory
or business is a good example.)
Evolution theory, OTOH, seems to say that biological "factories"
ranging in size from organelles to organs can develop without benefit
of skill or information resources, and without the need of even
short-term compromises in productive use of energy or nutrient
resources.
The validity of this assumption seems to me at least as difficult to
prove as the various scenarios for abiogenesis.
~From: bk186@cleveland.Freenet.Edu (Julie Thomas)
~Newsgroups: talk.origins
~Subject: More on three and four chamber hearts
~Message-ID: <1992Apr9.050422.21424@usenet.ins.cwru.edu>
~Date: 9 Apr 92 05:04:22 GMT
~Organization: Case Western Reserve University, Cleveland, OH (USA)
~Lines: 85
I have often found that the more I learn about biology, the more
easier it becomes to become skeptical of evolution. Let's consider
our three to four chamber heart transition in more detail. At first,
I must confess that I thought this was really not a big deal. I could
envision some regulatory mutation working to to simply extend the
interventricular septum so it completely seperated the right and
left ventricles (although typical neo-Darwinian gradulism seemed
out of the question). My problem was that I could see no selctive
advantage in this. The standard line about increased efficiency
(meaning evolution works to increase efficiency?) didn't hold up to
scrutiny (as far as yours truly was concerned). But now I must
change my tune and become even more skeptical as evolving a four
chamber heart was MUCH more than just completely the
interventricular septum.
See my cartoons below for a schematic of the two types of heart.
Reptilian heart
1
!
! 2 3
!***! !*/ /*
* *
* ! *
* R ! L *
* ! *
* ! *
******
Mammalian heart
1
! 2 3
! / /
!*/**** /*
* ! *
* ! *
* R ! L *
* ! *
* ! *
******
1 = Pulmonary trunk (blood leaves for the lungs)
2 = Right atrium (blood enters from the lungs)
3 = Left atrium (blood enters from the body)
R = Right ventricle
L = Left ventricle
! = Interventricular septum
If you look at these figures, it becomes quite obvious that the ol'
"complete the septum" story just won't work. For if the reptilian
septum was completed, this would kill the reptile since the blood
from BOTH the right and left atrium could not enter the right
ventricle, thus it could not be oxygenated by the lungs.
In other words, blood from the right atrium must first travel
through a portion of the left ventricle. In mammals, not only is the
interventricular septum complete, but the right atrium opens into
the right ventricle. Thus, the change that would have to occur is far
more than a growing septum. The plumbing of the heart would also
have to change simultaneously. Any tales about how a shifting
atrium occurred?
But let's also look at interesting developmental consideration. In
humans, when the interventricular septum is completed in about 3
months gestational age, the atrial septum still possesses a
discontinuity where there is cross-talk between the two atria.
Thus, development does not show a "2 complete atrial chambers /1
ventricular chamber --> 2 complete atrial chambers/2 compete
ventricular chambers" transition which is what was supposed to
have happened in the reptile heart to mammal heart transformation.
~It always seems that if we find a similar pattern in embryological
development, we are supposed to have evidence for evolution. But if the
pattern differs, well........ Evolution can be such a paradigm! :)
~From: bk186@cleveland.Freenet.Edu (Julie Thomas)
~Newsgroups: talk.origins
~Subject: Re: More on three and four chamber hearts
~Message-ID: <1992Apr14.015325.813@usenet.ins.cwru.edu>
~Date: 14 Apr 92 01:53:25 GMT
~References:
<1992Apr9.050422.21424@usenet.ins.cwru.edu>
~Lines: 88
In a previous article, salem@pangea.Stanford.EDU (Bruce Salem) says:
>Did you see my posting from a couple of days ago in the
>developmental sequence of the four chambered heart in
>humans and its relation to the anatomy of two and three
>chambered hearts?
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" 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.
Are you suggesting that without evolution, we should expect, for example,
the heart to develop from some 12 chamber stage? And considering that
development proceeds from a single cell towards a complete multicellular
organism, I would expect earlier structures to be less defined.
>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.
The heart
>begins as a thickening 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.
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.
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 atrium. At
>this point the venous circulation enters 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 opposite ends of the heart. So the transformation
>of the pulmonary 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 its growth.
The funny thing is that when it does, there remains an opening
between atria.
> 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? 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!).
~From: bk186@cleveland.Freenet.Edu (Julie Thomas)
~Newsgroups: talk.origins
~Subject: Developing ideas on hearts.
~Message-ID: <1992Apr16.003637.3576@usenet.ins.cwru.edu>
~Date: 16 Apr 92 00:36:37 GMT
~Lines: 144
Let's look at the development of the human heart in more detail to
determine if it really helps the notion that "hearts evolved". For my
primary source, I'll use the text "The Developing Human" by Keith
Moore.
The first thing to note is the cardiovascular system is the first to
form. Blood actually begins to circulate in the embryo by three
weeks. Moore writes, "this precocious development is necessary
because the rapidly growing embryo needs an efficient method of
acquiring nutrients and disposing of waste products". Now recall
that the human heart begins functioning in a so-called primitive
form. This is usually seen as some kind of phylogenetic evidence. I
doubt this, as what it could also mean is that the embryo needs a
pump as soon as possible, and it employs the "primitive" pump
because it can't wait around for it to develop into the more complex
pump. Thus the "primitive" heart need not reflect phylogeny, it may
very well reflect the developmental need for some kind of pump as
soon as possible.
Secondly, the heart forms by first forming a heart tube. Ah, says the
evolutionist. This stage reflects that first "just so" story about a
blood vessel becoming enlarged, incorporating valves, and becoming
a primitive heart, that was brought up earlier. Unfortunately for the
tale, the details don't support the story line. First it should be noted
that the heart tube actually forms from the merging of TWO smaller
heart tubes which are laterally opposed. The two tubes fuse to
actually create a tube within a tube. Between the tubes is a
gelatinous tissue called 'cardiac jelly'. Now, given these details, the
story about an evolving blood vessel becomes quite a long shot. If
the story was true, the bipartite structure is not explained. What is
even more significant is that in some fish and amphibians, the heart
does start as a single tube. But in all other vertebrates, the heart
starts with the fusion of two regions. Thus at the beginning, the
hearts of fish/amphibia and other vertebrates differ radically in
development. How and why did this state of affairs evolve? We are
not talking about modifying later states of development, but we are
talking about starting off from a different subroutine. Finally, I
can't resist going back to the evolving vessel story.
Measurements in the chick embryo show that while the heart tube
can easily fill with blood while it is relaxed, it cannot contract
sufficiently to reduce the lumen of the tube to provide for efficient
propulsion. This mechanical difficulty is resolved by the cardiac
jelly. It provides the medium by which a force of relatively modest
contraction of the myocardium is transmitted radially toward the
endocardium with resultant closure of the lumen. Once the
musculature of the ventricle builds up, this jelly is no longer needed.
Thus it seems that notions of contracting blood vessels are far too
simplistic. Even if they contracted, they might not have been able
(as seen by this evidence) to reduce the lumen enough to give a
substantial force of propulsion.
Now lets turn to the development of the chambers. Moore
emphasizes that these events occur concurrently. After fusing the
two tubes, the tube within a tube elongates and develops alternate
dilations and constrictions resulting in the formation of the various
chambers. The atrial chamber grows a septum and the completion of
this septum is actually quite involved and depending on the stage,
various perforations are made and discarded. In fact, because of
fetal circulation, a perforation (the foramen ovale) is maintained
throughout fetal life as the lungs are bypassed. It isn't until birth
that this hole closes and pulmonary circulation is established. The
right atrium forms by incorporating part of the sinus venosus. The
left atrium forms mostly by incorporating proximal parts of the
pulmonary vein. The interventricular septum concurrently grows to
divide the ventricles. Now at no time does the septum grow so that
the two atria pour into the left ventricle. The system develops so
that with the growing interventricular septum, the right atria pours
into the right ventricle and vica versa. I find this significant since
this does not reflect the supposed reptile to mammal change (as
outlined in my previous posts). Furthermore, the manner in which
the left atria forms is most instructive. It's formation is tied to
the prior existence of the pulmonary vein. Yet a pulmonary vein
clearly implies an oxygenating organ, and pulmonary artery. Now a
pulmonary artery obviously implies that the heart must be sending
blood in two directions: to the body AND the oxygenation organ.
Thus, the development cannot be reduced to pieces and parts. The
whole thing has to be there. If this evolved, surely some sort of
saltation is called for as gradualistic microevolutionary changes
must travel through many levels which are not only lacking
advantages, but would actually be disadvantageous.
Does all this really help the notion that "hearts evolved"? I really
don't think so. First, let me sound like a creationist. In this case,
ALL mutations which affect the heart in an observable manner are
deleterious (although I'm quite sure there are many neutral ones
which are not picked up due to a lack of mutant phenotype). When
development is changed, we get a heart DEFECT. Thus, the
development of the heart must be fine-tuned so that significant
changes result in deleterious effects. This is certainly not a
friendly environment for notions of reshaping the system due to
mutations.
Secondly, the development of the heart underscores the final forms
of different hearts, namely, there are significant differences. If
similarity counts as evidence for evolution, differences ought to
count against. None of this is certain, of course, however it ought to
raise some red flags when we hear stories about hearts "a-changin".
Thirdly, the similarities need not imply relationship. For example,
the heart tube might not reflect some ancient form. In fact, it
probably exists only because the embryo needs to recruit a pump as
soon as possible to continue development. And a tube can form more
quickly than a complicated four chambered heart.
In the end, since the evidence is only circumstantial, it's basically a
judgment call. For my part, speaking from my heart, in an attempt
to circulate some ideas, I am not convinced by the evolutionary story
even when it is pumped up with similarities. :) I am unable to
simply hand-wave away the differences, the similarities are not
compelling, and the empirical data gives us reason to suspect that
developing hearts don't like to change patterns, and no reason to
suspect they do or ever have.
Add to this all the problems with the "just so" explanations. Would
the three to four heart chamber transition really be such an
advantage? I already brought up runnin lizards and lazy crocs which
seem to throw a monkey wrench in this little story. But there is
another aspect. Mixing blood simply means the concentration of
dissolved oxygen in the blood is going to be less. Now increasing the
efficiency of the heart usually means getting more oxygenated blood
to the body. But instead of going through all this organ
restructuring, an organism could enjoy the same benefit with a few
simple point mutations in the hemoglobin so that it would be
saturated at lower concentrations of dissolved oxygen. In other
words, the oxygen dissociation curve could be shifted to the left by
such a mutation making it possible for the hemoglobin to load and
unload oxygen at lower concentrations. Thus, if efficiency
was the selective pressure, one would expect this route to have been
monopolized instead of organ transformation since it is more likely
~to arise because it involves simpler changes giving the same benefit
s. These considerations cause me to suspect that evolutionary
reductionism is missing the mark. Notions of reptiles evolving
mammalian hearts treats organisms as pieces and parts, while if
anything is to be learned from development, it is that organisms
develop and exist as whole beings. Perhaps the mammalian heart
exists because it exists in a mammal.
~From: bk186@cleveland.Freenet.Edu (Julie Thomas)
~Newsgroups: talk.origins
~Subject: Another heart attack.
~Message-ID: <1992Apr18.125630.4094@usenet.ins.cwru.edu>
~Date: 18 Apr 92 12:56:30 GMT
~Lines: 215
Well, I was about to leave this topic, but it seems another actor has
walked onto the stage, Mr. Lungfish. Let's set the context for his
part in the story. (Using Torey's and Feduccia's "Morphogenesis of
Vertebrates).
The structure of the heart in the Chondrichthyes and actinopteryian
Osteichthyes conforms to the general pattern of four-chambers-in
series. Blood from the body enters the sinus venosus, then the
single atria, then the single ventricle, and leaves via the truncus to
travel to the gills, where it is oxygenated, and then goes to the body
WITHOUT returning to the heart.
As we know, terrestrial vertebrates have pulmonary and systemic
circuits operating in parallel along with divided hearts. How did
this rather major change come about? To put it simply, what good is
1/2 a pulmonary artery, 3/2 of atria, or a 'lung' that is not connected
to the circulatory system?
Well, we don't have any living rhipidistian crossopterygians which
are said to have been the ancestors of the first amphibians. But
wait, we do have that living fossil, that member of the other group
of Crossopterygii, the coelacanth. Since this critter hasn't changed
over the hundreds of millions of years, and it is another
crossoptterygian, you would sort of expect some crucial insight
from this critter's heart. According to T&F (pg 422) their:
"internal anatomy is.....so specialized as to be little indicative of the
basic conditions we should like to know".
Now I don't know about anyone else, but this looks like hand-waving
in response to information that is not supportive or even
contradictory of our story, "The Heart That Evolved". It probably has
only a fish heart! Oh well.
Anyway, have no fear, as we do have the living relatives (so it is
said) of the crossopterygii, the Dipnoi, or lungfishes. Yes, indeed,
the lungfish have a four-chambered heart which operates with a
parallel circulatory system. According to this twist in the plot, the
lungfish reflect the state of the original amphibian ancestor, and the
reptilian ancestor, along with the bird and mammal ancestor. Thus,
the origin of the four-chambered heart has been solved, and they all
lived happily ever after.
But hold on a minute. If you ask me, Mr. Lungfish makes the heart
story even more implausible. Why? Because we are STILL left with
a lungfish which evolves a 2 atria/2 ventricle heart with pulmonary
circuit system from fish with a 1 atrium/1 ventricle heart and NO
pulmonary circuit. The origin of this four chambered heart is still
not resolved, and in fact, the situation is worse. For now it is no
longer possible to appeal to the three-chambered hearts of
amphibians and reptiles to serve as intermediate structures! We are
left with the same problem, but now we're empty handed.
The amphibian/reptilian heart evolved AFTER the the lungfish heart,
so certainly any information from these systems is not applicable.
In short, not only do we have no fossil evidence, but we have now
lost our developmental evidence. Thus, we have NO evidence, but we
have a belief that is supposed to be scientific.
Now, I suppose one could appeal to the amphibian heart/reptile heart
as "possible" states which "might have occurred". But I wouldn't
even accept these speculations. Why? For one thing, it's easier to
lose a structure than gain one. That is, the amphibian/reptilian
heart would be "intermediate" examples where the four chamber
structure was LOST, not acquired. A situation where a heart is
changed so that the septum no longer completely forms is NOT
evidence for the ability to acquire new chambers and new
circulatory systems. It is no longer possible to use the
amphibian/reptilian systems as intermediates to explain how some
fish evolved a four-chamber heart in parallel. Mr. Lungfish, while
thinking himself the hero of the story, really turns out to be a
villain.
But what of our reptile to mammal transition? Let's not forget to
let Mrs. Crocodile play her part. She too has a four chamber heart,
much like that of mammals and birds, making her heart more similar
to a humans than to a lizard. In fact, her interventricular septum is
structured differently than other reptiles, causing T&F to assert:
"this septum is a vertical septum rather than a horizontal one , and appears to be a new evolutionary
development, which is not to be homologized with the
interventricular septa of lizards, snakes, and turtles". (pg 425).
Now I'm confused. How is this septa a new evolutionary development
if it, like that of the bird and mammal, supposedly reflects that
lungfish to mammal/bird line? Anyway, the significant point is that
the septa are not homologous. Now let's go back to that old reptile
to mammal transition problem. If you'll recall, the problem I alluded
to was that in reptiles (but not crocs) BOTH the right and left atria
empty into the left ventricle. If Mr. Lungfish's contribution to
the plot is considered, the problem is not how to separate the atria,
but now it's how to sequester them. Either one seems like trouble to
me. What selective advantage was there in taking a heart where the
the right atrium enters the right ventricle and shifting it so that it
enters the left ventricle where the blood can now mix?
This problem is further emphasized in the amphibians. According to
T&F, (pg 423):
"modern Amphibia, with their incompletely divided hearts, may
illustrate degeneracy rather than primitive intermediacy between
fishes and amniotes".
Well, there goes the infamous story line! No more can we use
"efficiency" as our selective guide. For hearts in amphibians and
reptiles evolved to a state of inferior efficiency. But what about all
that talk about efficiency? Didn't people REALLY believe it? Or was
it a smokescreen? Wouldn't some amphibian which developed a less
efficient heart be at a disadvantage than one that did not? Afterall,
we heard time and again about how a more efficient heart would be a
selective advantage. If a completely separated heart was an
advantage, then an incompletely separated heart would be a
disadvantage. Thus, if I was supposed to seriously entertain that
just so story, it seems only fair to expect those who believed it to
also take it seriously and explain how evolution worked to select for
an inefficient system among those with efficient systems.
As it turns out, the heart story has taken a turn over some figurative
aortic arch for the worse.
But there is one more aspect of Mr. Lungfish that I want to look at.
Mr. Lungfish has lungs and an efficient circulatory system. These
come in handy when droughts occur. Wait a minute! Isn't this the
scenario for the fish to amphibian transformation? It sure is, yet
Mr. Lungfish hasn't evolved one bit towards wandering onto the land
in over 300 million years of evolution! In fact, Mr. Lungfish has
hardly changed although he has sat poised for 300 million years at
the state and environment which supposedly gave rise to amphibians.
These facts make you wonder about that other story about fish and
amphibians.
Now in response to some of the complaints I've been getting, let me
outline some of the points which I have gotten out of this inquiry.
1. Many believe "hearts evolved". They consider this a scientific
belief. Yet they admit that our evidence for this belief is meager.
So why are people getting upset about me not accepting a belief
which is supposedly scientific yet which lacks good evidence?
2. I have learned again that similarity need not reflect some
phylogenetic relationship. We saw this with sharks and mammals
when it came to the circulatory pattern associated with the yolk
sac. In my mind, this weakens the appeal to similarities to support
evolution. If the vessels of the reptile were not descended from the
shark even though they are identical, then it becomes entirely
plausible that the heart of the mammal was not descended from the
lungfish even thought they are quite similar.
3. The hearts of amphibians and reptiles start out from different
initial states. Thus, this is not an example of "tweaking at the
peripherals". This weighs heavily in my mind against some
evolutionary transformation. On this point, I have proceeded from
agnosticism to skepticism.
4. We are still left with no account of how the four-chambered
heart arrived on the scene. Mr. Lungfish has actually worked to
remove all the developmental circumstantial evidence by placing
this transformation in the fish. If you don't have a clue as to how it
happened, I see no good reason to think it could have happened.
5. The ad hoc nature of "just so" stories have been exposed. Their
only limit is one's imagination. Here is a case where the definitive
word is supposed to rest on someone's musings. Furthermore, the
just so story about efficiency actually turns in on itself when we
realize that hearts evolved to less efficient states. The take home
message is that just so stories are quite like the creationsist's "God
did it" story. In both cases, the "explanation" seems to be able to
explain anything. The only thing just so stories have on the
creationist's stories is that the former are more imaginative. In all
honesty, they usually read like modern myths (to me), an analogue to
the camp fire stories about the distant past which tell us why
things are like the way they are today.
6. I've also learned that the fallacy of card stacking is common in
evolutionary thought. If differences are found which do not support
the story, or even are contrary to the story, we either complain
about them being found in cousins (although this doesn't stop us from
using cousins to support ancestry), or we give them a label and
assign them to a "special" category (an effective way of dismissing
contrary evidence) like "regressive evolution" or "highly
specialized".
7. I've learned that a creature can be poised to transform,
yet can refuse to transform for hundreds of millions of years.
8. Finally, while I fully concur that the creationists are just plain
wrong when they say there is no such thing as an advantageous
mutation, here is a system where all phenotypically observable
mutations are deleterious. To date, the expirical evidence certainly
supports the following hypothesis: -->Concerning the development of
the circulatory system, there is no such thing as an advantageous
mutation<--. I wonder how many other systems this hypothesis
would apply to (BTW, it's both predictive and falsifiable for those
who worry about such things)?
Now if you take this hypothesis, with it's supporting set of data and
add it to the considerations concerning "teaking" in #3, and consider
the lack of evidence and an explanation for the belief that hearts
did evolve, we seem to be falling into a position where it looks like
hearts did not evolve, at least in a neo-Darwinian sense.
All in all, this has been an experience which has shown me more than
the specifics associated with hearts. I've gained insight into the
aspects of the biological world as a whole and have also seen how
the paradigm of evolution functions as a guide. I have enjoyed this.
Now, I'll try to get back to that other topic and post on it later.
Thanks to all those who have interacted!
--
Joel Roth jroth@aegis.org (international)
Brahma Kumaris World jroth@aegis.or.jp (within Japan)
Spiritual University 1-2-15-501 Nakamichi, Higashi Nari ku,
Raja Yoga Center, Osaka Osaka, Japan 537, 81-6-971-7251
