Freethought & Rationalism Archive

Secular Elation · 09-04-2002, 03:38 PM

Anyone heard of this one?

Recently, a person I am familiar with made this argument, along these lines, against evolution:

Quote:

Evoltuion conflicts with giraffes. Notice how the head of the giraffe is located on top of a neck that rises several feel upward in vertical direction?

There needs to be lots of blood pressure to deliver blood to the head way up there at the neck, because the blood must be driven directly upward and conflict with gravity pulling it down.

Well, what would happen if the giraffe moved his head down toward the ground, so that his neck is nearly horizontal? The blood pressure would accumulate in the giraffes head, because the blood pressure is at the same intensity, but there is far less pull from gravity. Therefore, it would be like an ultimate blood rushing to the head, and would cause damage in the head consequently.

This conflicts with evolution because why wouldn't the giraffe 'adapt' or 'evolve out' this weakness?

Give me a break...like a giraffe's head is going to burst for moving it downward! Geez!

[ September 04, 2002: Message edited by: Secular Elation ]

Doubting Didymus · 09-04-2002, 03:46 PM

Um, for the same reason we havent adapted to walk around on our hands all the time? Giraffes don't need to walk around with horisontal necks, they walk around with heads held high to look for predators and feed from high trees. They are not adapted to be harpoons.

Out of interest, if this is true about giraffe blood pressure, how do they bend down to drink? I suspect that blood pressure is not nearly as much of a problem for giraffes as this person makes out.

(aside: the implications of this argument are interesting. Why did giraffes not evolve out of this problem? Well, why were they created with this problem? Obviously, god wants giraffes to suffer.)

Undercurrent · 09-04-2002, 03:47 PM

Quote:

Originally posted by Secular Elation:
Anyone heard of this one?

He seems to be arguing for the non-existance of giraffes more than anything else. Clearly giraffes routinely lower their heads to drink without getting brain damage.

m.

DireStraits · 09-04-2002, 03:54 PM

Evoltuion conflicts with giraffes.

DS: Troll alter! I mean alert. But it's kinda slow right now so I'll bite.

Notice how the head of the giraffe is located on top of a neck

DS: Yeah, that's where most heads are located. That's why they are called heads.

that rises several feel upward in vertical direction?

DS: "Feel upward in a vertical direction"? Why you ols horn dog, you!

There needs to be lots of blood pressure to deliver blood to the head way up there at the neck, because the blood must be driven directly upward and conflict with gravity pulling it down.

DS: I think I know what he means by "lots of blood pressure", but, so far so good. Giraffes have higher blood pressure that any other mammal, I would think.

Well, what would happen if the giraffe moved his head down toward the ground, so that his neck is nearly horizontal? The blood pressure would accumulate in the giraffes head, because the blood pressure is at the same intensity, but there is far less pull from gravity.

DS: Really? The difference in the accelration due to gravity will be far less in the horizontal than the vertical. Hmmm. How tall do you think giraffes grow to?

Therefore, it would be like an ultimate blood rushing to the head, and would cause damage in the head consequently.

DS: Ever heard of valves and vaso constriction?

This conflicts with evolution because why wouldn't the giraffe 'adapt' or 'evolve out' this weakness?

DS: They don't need to. They can reach down to the ground with their heads - indeed HAVE to in order to drink.

scigirl · 09-04-2002, 06:59 PM

Wow I'm using my animal physiology (Eckert 4th edition) book again!

Ok I don't understand the argument - is the author trying to say that giraffes can't lower their heads? I've seen them lower their heads!

Heh circulatory regulatory mechanisms had to evolve before giraffe neck length could evolve. So what?

Quote:

The problems of pooling and maintaining capillary flow are acute in species with long necks. For instance, when the giraffe is standing with its head raised, its brain is about 6 meters above the ground and over 2 meters above the heart. If the arterial pressure of blood perfusing the brain is to be maintained at around 98 mm Hg, aortic blood pressure must be 195-300 mm Hg near the heart. Aortic blood pressure greater than 195 have been recorded...Arterial pressures in the legs of the giraffe are even higher than aortic pressures; to prevent the pooling of blood, the giraffe has large quantities of connective tissue surrounding the leg vessels. As the giraffe lowers its head to the ground, arterial blood pressure at the level of the heart is reduced considerably, thus maintaining a relatively constant blood flow to the brain. The wide variation in aortic pressure as the giraffe moves its head position could lead to extensive pooling of blood...pooling most likely is prevented by vasoconstriction of these peripheral vessels when the head is raised. Conversely, when the head is lowered, extensive vasodilation of arterioles leading to capillary beds other than those in the head probably maintains flow despite the lower aortic pressure.

scigirl

monkenstick · 09-04-2002, 07:10 PM

i have encountered this argument before - i think the pressure problem is alleviated by its sinuses or something

heres something on it, scroll down

<a href="http://www.chiroweb.com/archives/19/26/04.html" target="_blank">http://www.chiroweb.com/archives/19/26/04.html</a>

gallo · 09-04-2002, 07:44 PM

Holy Jesus! What crap creationists throw about.

If we could meet in person, I could show you on your own arm the mechanism that prevents blood flow away from the heart in the veins. It doesn't matter what kind of centrifugal forces you put on your extremities, blood will not flow away from the heart in the veins. That is why in coronary bypass operations the veins (extracted from the leg in most cases) are turned around when they are grafted. The end that is furthest away from the heart in the vein is grafted in place to be nearest the heart. The reason is that there are valves in the veins that prevent reverse blood flow. If it is grafted in a reverse orientation, there is no problem. If it isn't reversed, then if the particular segment has a reverse flow valve, you get an immediate and total coronary occlusion.

The giraffe has similar valves in the arteries of the neck that occlude with increased pressure. Thus, if a giraffe lowers its head, the increased pressure causes the valves to close and restrict the blood flow to the head.

So now I'm waiting for the creationist explanation as to why arterial valves in the neck of the giraff that restrict blood flow are necessarily the result of POOF the Creator if venous valves that serve the same function exist in most extant tetrapods.

Albion · 09-04-2002, 07:56 PM

OK, so he's saying that the giraffe didn't evolve because its present configuration is impossible? And yet giraffes still exist, impossible configurations notwithstanding. This is supposed to be proof of God or something?

Sounds like giraffes aren't the only ones having problems with blood flow to the brain.

Wyz_sub10 · 09-05-2002, 05:53 AM

Quote:

Originally posted by Albion:
OK, so he's saying that the giraffe didn't evolve because its present configuration is impossible? And yet giraffes still exist, impossible configurations notwithstanding. This is supposed to be proof of God or something?

Sounds like giraffes aren't the only ones having problems with blood flow to the brain.

You beat me to that one.

"It happened, but it can't really happen."

So it isn't possible to have happened through evolution, but of course the godidit theory handles this one exceptionally.

[ September 05, 2002: Message edited by: Wyz_sub10 ]

Oolon Colluphid · 09-05-2002, 06:12 AM

So it was designed, yeah? At the risk of boring regulars once again with this... ask the idiot why the giraffe has a recurrent laryngeal nerve that goes about fifteen feet out of its way, looping under the aorta by the heart, on its route from one side of the neck to the other.

Sheesh!

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

09-04-2002, 03:46 PM	#2
Doubting Didymus Veteran Member Join Date: Jul 2002 Location: East Coast. Australia. Posts: 5,455	Um, for the same reason we havent adapted to walk around on our hands all the time? Giraffes don't need to walk around with horisontal necks, they walk around with heads held high to look for predators and feed from high trees. They are not adapted to be harpoons. Out of interest, if this is true about giraffe blood pressure, how do they bend down to drink? I suspect that blood pressure is not nearly as much of a problem for giraffes as this person makes out. (aside: the implications of this argument are interesting. Why did giraffes not evolve out of this problem? Well, why were they created with this problem? Obviously, god wants giraffes to suffer.)

09-04-2002, 03:54 PM	#4
DireStraits Junior Member Join Date: Feb 2002 Posts: 81	Evoltuion conflicts with giraffes. DS: Troll alter! I mean alert. But it's kinda slow right now so I'll bite. Notice how the head of the giraffe is located on top of a neck DS: Yeah, that's where most heads are located. That's why they are called heads. that rises several feel upward in vertical direction? DS: "Feel upward in a vertical direction"? Why you ols horn dog, you! There needs to be lots of blood pressure to deliver blood to the head way up there at the neck, because the blood must be driven directly upward and conflict with gravity pulling it down. DS: I think I know what he means by "lots of blood pressure", but, so far so good. Giraffes have higher blood pressure that any other mammal, I would think. Well, what would happen if the giraffe moved his head down toward the ground, so that his neck is nearly horizontal? The blood pressure would accumulate in the giraffes head, because the blood pressure is at the same intensity, but there is far less pull from gravity. DS: Really? The difference in the accelration due to gravity will be far less in the horizontal than the vertical. Hmmm. How tall do you think giraffes grow to? Therefore, it would be like an ultimate blood rushing to the head, and would cause damage in the head consequently. DS: Ever heard of valves and vaso constriction? This conflicts with evolution because why wouldn't the giraffe 'adapt' or 'evolve out' this weakness? DS: They don't need to. They can reach down to the ground with their heads - indeed HAVE to in order to drink.

09-04-2002, 07:10 PM	#6
monkenstick Regular Member Join Date: Jul 2002 Location: Australia Posts: 214	i have encountered this argument before - i think the pressure problem is alleviated by its sinuses or something heres something on it, scroll down <a href="http://www.chiroweb.com/archives/19/26/04.html" target="_blank">http://www.chiroweb.com/archives/19/26/04.html</a>

09-04-2002, 07:44 PM	#7
gallo Regular Member Join Date: Jun 2001 Location: Houston, TX, US Posts: 244	Holy Jesus! What crap creationists throw about. If we could meet in person, I could show you on your own arm the mechanism that prevents blood flow away from the heart in the veins. It doesn't matter what kind of centrifugal forces you put on your extremities, blood will not flow away from the heart in the veins. That is why in coronary bypass operations the veins (extracted from the leg in most cases) are turned around when they are grafted. The end that is furthest away from the heart in the vein is grafted in place to be nearest the heart. The reason is that there are valves in the veins that prevent reverse blood flow. If it is grafted in a reverse orientation, there is no problem. If it isn't reversed, then if the particular segment has a reverse flow valve, you get an immediate and total coronary occlusion. The giraffe has similar valves in the arteries of the neck that occlude with increased pressure. Thus, if a giraffe lowers its head, the increased pressure causes the valves to close and restrict the blood flow to the head. So now I'm waiting for the creationist explanation as to why arterial valves in the neck of the giraff that restrict blood flow are necessarily the result of POOF the Creator if venous valves that serve the same function exist in most extant tetrapods.

09-04-2002, 07:56 PM	#8
Albion Veteran Member Join Date: Jul 2002 Location: US east coast. And www.theroyalforums.com Posts: 2,829	OK, so he's saying that the giraffe didn't evolve because its present configuration is impossible? And yet giraffes still exist, impossible configurations notwithstanding. This is supposed to be proof of God or something? Sounds like giraffes aren't the only ones having problems with blood flow to the brain.

09-05-2002, 06:12 AM	#10
Oolon Colluphid Contributor Join Date: Sep 2000 Location: Alibi: ego ipse hinc extermino Posts: 12,591	So it was designed, yeah? At the risk of boring regulars once again with this... ask the idiot why the giraffe has a recurrent laryngeal nerve that goes about fifteen feet out of its way, looping under the aorta by the heart, on its route from one side of the neck to the other. Sheesh!

Freethought & Rationalism Archive

The archives are read only.