Doubting Didymus

Nice to see you back into the fray, scigirl. Did you blitz your exams?

I am about to start my anatomy strand myself. What am I in for?

scigirl

No I'm taking a break.

What are you in for? Well anatomy is tough, but a lot of fun, and very informative.

scigirl

Doubting Didymus

You call arguing with vanderzyden a 'break'? How masochistic of you!

lpetrich

Vanderzyden:
First, allow me to thank you for recalling this to my attention, as I have not considered the beauty and complexity of the circulatory system for a long time. I appreciate this opportunity.

However, the human circulatory system goes through some major reorganization as it grows, especially in the first few weeks. It starts out in a fashion suitable for a fish! The embryo has gill arches and gill pouches that are serviced by appropriately-arranged blood vessels:

Heart ->
Ventral Aorta ->
Aortic Arches that parallel the gill bars on each side of the body ->
Two Dorsal Aortas, one on each side of the body

Here are <a href="http://www.uoguelph.ca/zoology/devobio/210labs/arch1.html" target="_blank">some diagrams for the chick embryo</a> -- the human-embryo version looks remarkably similar! Or check out <a href="http://www.uta.edu/biology/campbell/cva/3452circ.htm" target="_blank">these comparisons</a> (the rest of that comparative-anatomy site is also very good!).

As the embryo grows, the gill arches and the gill pouches either get reused or get resorbed (the first gill arch set becomes the jaws), and the same happens to the aortic arches. Arch set 3 becomes the internal carotid arteries, arch set 4 becomes the systemic arch, becoming effectively an aorta part, and arch set 6 becomes the pulmonary arteries. Interestingly, only one of arch set 4 does aorta duty -- the left one drops out in mammals and the right one in birds.

Also, the early embryo has vitelline arteries and veins -- these service the yolk sac! Now why would an embryo in a womb need yolk???

And the heart starts off like a fish heart -- it has two chambers and one blood path through it. As it grows, its chambers split in two and the blood path splits into two blood paths. An incomplete splitting produces the "Blue Baby" birth defect, the "tetralogy of Fallot".

I wonder if Vanderzyden would have appreciated it if his daughter had been born with some lovely shade of blue -- from an incompletely-split heart.

-- no admission of the (a) inherent complexity and fascinating function of the circulatory system in general or (b) the transition in particular

Totally irrelevant.

-- an intense focus on potential defect, which inhibits the consideration of the overall context in which the "defect" might have distinct and significant advantages

And this is the best of all possible worlds (sarcasm).

-- no offer of a "superior" design

Mr. Darwin did -- connection of placental vessels directly to the heart. The pulmonary circulation could have a branch that goes to the placenta, as if it was some extra lungs. And the circulatory system could have developed in an adultlike form from the beginning.

-- no mention of the inadequacy of cardiovascular substitutes, such as artifical hearts.

Totally irrelevant.

Placement of the umbilicus above the liver means that the bulk of the liver would not get highly oxygenated blood, as it would receive "leftover" blood at considerably lower low pressure (since it would be on the pulmonary side of the fetal cardiovascular system).

No real disaster, since it does not have to be very active.

Yet again, we see a failed attempt to raise suspicion about the necessity for a designer.

That's not an absolute impossibility -- but the designer(s) would have to be VERY uncreative.

Evolution does not work. Period.

I wonder what VZ would say if he got infected by some multi-drug-resistant microbe. That's the result of evolution in action, whether he likes it or not.

Certainly, MrD has not been persuasive of its successful operation in this case. Nor has he shown the cardiovascular system to be poorly designed.

Risking being a Blue Baby is not what I consider sensible design.

I find it amazing that a human can dare to play the role of design consultant to the Creator.

I suggest that VZ look around at our technology -- if we, as a species, were incapable of producing high-quality designs, could we have possibly created the marvels that we now take for granted?

And many of our designs improve on our physical and mental features in various ways. Our muscles have the deficiency that they cannot lock into place, which would be very convenient for carrying stuff. However, such locking is straightforward to build -- consider a car's brakes. Also, writing is more durable than memory and computers outperform our brains in arithmetic and bookkeeping and suchlike.

MrDarwin must be very highly qualified, although he is incapable of choosing the place of his birth or preventing his eventual death.

SO WHAT???

We don't have to be omnipotent or eternal in order to be able to come up with good designs.

He does not have power in this very small thing, and yet he is so bold to criticize the design of the wonderfully spectacular human body.

Except that these are not so small as VZ thinks. The first one is impossible to control and the second one would require a lot more knowledge of body architecture than we already have -- like some way to regenerate without turning into a cancerous mass.

Tell us, MrDarwin, do you think you will stand before God with such pitiful defiance?

Be careful, O VZ. God might just take MrDarwin's side -- he could concede that he could have done a better job with fetal circulation.

Very slight defects are thought to occur in one in every fifteen babies. Oh, don't blame God. Blame the ancestors who smoked cigarettes, were alcoholics, or got into some other kind of trouble.

However, a fragile design can legitimately be held against its designer(s).

It would seem that you would like to turn this into a religious discussion, scigirl. I would rather limit our religious dialogue in this particular discussion to "design" and "designer", and the implications that are directly related, thanks.

VZ, accept that you were the one who started it, with talk about "standing before God". Or are you going to brag about how irreligious you are, O VZ?

(VZ's whining deleted)

lpetrich

Or more seriously, why is it necessary to give birth through the pelvic girdle? GIving birth forward, in C-section fashion, would be much less of a squeeze, since there is no bone to pass through.

However, this is understandable as a result of evolution. If one "gives birth" by laying lots of small eggs, then "giving birth" through the pelvic girdle presents no real difficulty. But if one is stuck with that arrangement, one will have great difficulty if one tries to turn it into giving birth to a big baby.

I hope it's OK for me to comment on this subject, as I have above.

[ October 17, 2002: Message edited by: lpetrich ]</p>

lpetrich

And if I had to pose such a challenge, it would be aphids and their bacterial symbionts -- why do aphids need bacteria living inside of them to produce dietary supplements, when a reasonable designer would have given aphids all the biosynthesis capabilities needed to live off of plant sap?

lpetrich

Here's <a href="http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v407/n6800/full/407081a0_fs.html" target="_blank">a report on that aphid symbiont's genome</a>.

Any opinions on constructing an "aphid challenge" for creationists?

Oolon Colluphid

I made the same sort of point in my long list ref Convoluta roscoffensis flatworms and their algae... though I prefer the aphid example (which will make it into that list eventually!)Same really goes for ruminants, and my favourite (since I found the info myself ) the Chinese grass carp. Why no enzymes to digest cellulose?

Oolon

MrDarwin

Vanderzyden, I am quite perplexed by your reaction. Where have you seen me criticize God? In fact, where have you seen me introduce God into this discussion at all? To the best of my knowledge, it was a discussion of biological systems, and how they demonstrate suboptimal design. If anything, I am criticizing the ability of evolution to produce optimal designs. Please take care to note which forum we are in.

scigirl

lpetrich and MrDarwin - thanks for the clarifications and insights. I haven't yet taken embryology, but I imagine that when I do, I'll be posting evidence for evolution here nearly every day.

lpetrich - good point about the pelvic canal. Another weird facet of reproductive biology - why doesn't the fallopian tube directly connect to the ovary? If it did, you wouldn't have ectopic pregancies. I just can't see any advantage to exposing the ovum to the peritoneal cavity.

Vanderzyden,

I started a new thread about medicine for you <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=001553" target="_blank">here</a>. I also added some comments this morning addressed to you about this thread here, but I didn't want to change the topic off biology, so I added them to my thread.

scigirl