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#1 HydrogenBond

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Posted 06 December 2010 - 08:07 PM

This idea came to me the other day. Red bloods do not have DNA. Their job is connected to the exchange of O2/CO2 between all the other cells via hemoglobin. These cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages.

Here is the scenario. Hypothetically, say the red blood cells had nuclei/DNA and were able to replicate within the blood. Could this account for the large size of dinosaurs?

The logic is, if the red blood cells could divide in the blood, the amount of O2/CO2 exchange would amplify with time. As long as there is sufficient food input, the accelerating level of possible O2/CO2 exchange could support accelerating cell division and activity, as well as provide a very rich O2/fuel ratio in the muscles. The neurons don't replicate after a certain point. Plus there is a blood/brain barrier. If this was still in effect, the brain size may not grow in the same accelerating, but will nevertheless be fed high levels of O2 for high activity.

#2 CraigD

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Posted 06 December 2010 - 09:30 PM

This idea came to me the other day. Red bloods do not have DNA. Their job is connected to the exchange of O2/CO2 between all the other cells via hemoglobin. These cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages.

Here is the scenario. Hypothetically, say the red blood cells had nuclei/DNA and were able to replicate within the blood. Could this account for the large size of dinosaurs?


Though there’s a limit to how much we can know about the blood of long-extinct animals like dinosaurs, it’s a pretty safe guess that the big dinosaurs’ (eg theropods and sauropods) red blood cells (erythrocytes) did have nuclei. The only vertebrates with non-nucleated mature erythrocytes are the mammals. There’s a pretty strong paleobiological consensus that the big dinosaurs were genetically closely related to modern birds, which aren’t mammals.

The logic is, if the red blood cells could divide in the blood, the amount of O2/CO2 exchange would amplify with time. As long as there is sufficient food input, the accelerating level of possible O2/CO2 exchange could support accelerating cell division and activity, as well as provide a very rich O2/fuel ratio in the muscles.

This is rather the reverse of what we see in modern mammals on non-mammal vertebrates. We mammals have higher aerobic metabolism per unit mass than reptiles, birds, etc, not despite our nucleus-free erythrocytes, but because of them. While they don’t live long or self-repair well, our erythrocytes also don’t use any of the oxygen they deliver to our other cells, allowing us to supply oxygen at a high rate to our big brains and powerful muscles.

To the best of my knowledge, even nucleated erythrocytes don’t replicate in the blood. Only their precursor cells - hematopoietic stem cells – are capable of replication.

In short, and taking some liberties with the concept of “improved” in a biological context, non-nucleated erythrocytes can’t be improved upon by giving them nuclei, because they are an improvement on nucleated erythrocytes.
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#3 Rade

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Posted 07 December 2010 - 12:15 AM

Red bloods do not have DNA... Hypothetically, say the red blood cells had nuclei/DNA and were able to replicate within the blood. Could this account for the large size of dinosaurs? ...The logic is, if the red blood cells could divide in the blood, the amount of O2/CO2 exchange would amplify with time


First, only mammal RBC do not have DNA in adults, all other vertebrates (fish, reptiles, birds, amphibians) have RBC with a nucleus as adults. However, the nucleus is non-functional (does not undergo mitosis) in RBC in vertebrates where it is found. In early stages of mammalian development RBC do have a nucleus, but the nucleus is lost. Thus, there has been strong selective pressure in all known vertebrates, big and small, for RBC to: (1) either lose a nucleus, or, (2) if a nucleus remains, to make it inactive and stop mitosis (RBC division) while the RBC is moving through blood vessels.

There are problems with your statement concerning animal size and RBC mitosis.

One problem is that there are many large mammals today (whales, elephants) and they do not have RBC with a nucleus, so, clearly vertebrates can become large for reasons other than having RBC with nucleus. Then, consider the giant squid, genus Architeuthis,which is an invertebrate with no red blood cells that can reach a length of 50 feet. Clearly, large animal size is not correlated to presence of nucleated RBC, nor RBC at all, to carry O2.

Another problem is that the amount of O2/CO2 exchange would not amplify over time if RBC divided while moving within blood vessels, but would decrease. Relocating the process of RBC division to blood vessels defeats the function of the RBC, which is to carry O2 efficiently in a localized structure containing O2 carrying pigments, such as hemoglobin. There is a long evolutionary history of blood with O2 transported directly by the pigments scattered throughout the blood, not localized in RBC structures. This includes all animals known as invertebrates and early vertebrates, such as Amphioxus. It is not until early fish (such as lampreys)that localized RBC structures are found, and the nucleus is not functional while the RBC moves in vessels. Thus, from the get-go, the most efficient way for vertebrates to transport O2 was in RBC with non-functional nucleus. There is no logical reason to suggest that dinosaurs would deviate.

Then we have the problem that if the RBC had to allocate ATP energy into mitosis while it was moving in blood, that process would consume the vary O2 it was carrying, leaving less O2 to be delivered to the cells, the only reason RBC evolved. Also, is a problem of space competition within the RBC. The molecules and cell organelles needed for mitosis (nucleus for DNA, mitochondria for ATP) take up critical space and thus result in fewer O2 carrying molecules, such as hemoglobin. Yet another problem would be the loss of regulatory feedback of the RBC production process. With RBC cell division localized within bone marrow (or spleen or other organs as in primitive vertebrates and humans during fetal development), the production rate can be regulated in a localized manner by hormones. Consider the difficulty of trying to regulate RBC mitosis at 100 million different locations in blood vessels via hormones (at each individual RBC while it moves).

So, the answer to your hypothetical OP question is no. Are you aware that bone marrow with nucleated RBC has been found in dinosaur bones, as well as 10+ million year old frogs ? http://www.livescien...bonemarrow.html
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#4 HydrogenBond

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Posted 10 December 2010 - 10:57 AM

The idea of replicating red blood cells would add something similar to a turbo or supercharger effect, where more O2 exchange can occur at metabolism. Without altering the basic mechanics of an auto, simply by adding a supercharger, to add more air to combustion, we can increase performance. As such, for any DNA, adding red cell replication will supercharge it.

I would guess that the replicating red blood cells would be self limiting. Their own O2 rich state, which allows them to absorb O2 beyond their own needs, means the terminal electron acceptor concentration in their metabolism would shift to the oxidation side of the equation, making it harder to store food or energy value for replication. The blood would need to be rich in food value to compensate, thereby making sure the rest of the cells get their fill before we could expand the red blood cell supply.

I am looking at the energy side of the equation of life. Cells can't so anything without an energy supply. Even genetics becomes limited. But with a supercharger effect, even the DNA sees an increases in energy input which is conducive to mistakes such as mutations. Stages of evolution with diversity explosion benefits by extra energy.

As an analogy, we add a supercharge to the car. The extra performance makes the car sort of lopsided. We may need to upgrade the suspension, transmission, etc. With the extra boost of energy to the DNA, we also the have the R&D conditions for the future of selective advantage.

#5 maikeru

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Posted 12 December 2010 - 03:10 AM

1. Higher O2 percentages in the air during those times. More O2 = more available for metabolism and bigger body mass/higher metabolism. Studies suggest up to 35% O2 in the Cretaceous.

Analyses of the gases in these bubbles show that the Earth's atmosphere, 67 million years ago, contained nearly 35 percent oxygen compared to present levels of 21 percent. Results are based upon more than 300 analyses by USGS scientists of Cretaceous, Tertiary, and recent-age amber from 16 world sites.* The oldest amber in this study is about 130 million years old.


http://geology.com/usgs/amber/

2. Birds have air sacs that allow for unidirectional flow of air throughout their respiratory system, essentially allowing them to breathe "fresh air" each time rather than mixing "old" and "new" air like mammalian lungs do. I suspect many dinosaurs had a respiratory setup similar to birds, especially if they were highly active or theropods. More efficient respiratory system = less limits on large body size and higher metabolism.

The air sacs permit a unidirectional flow of air through the lungs. Unidirectional flow means that air moving through bird lungs is largely 'fresh' air & has a higher oxygen content. In contrast, air flow is 'bidirectional' in mammals, moving back & forth into & out of the lungs. As a result, air coming into a mammal's lungs is mixed with 'old' air (air that has been in the lungs for a while) & this 'mixed air' has less oxygen. So, in bird lungs, more oxygen is available to diffuse into the blood.


http://people.eku.ed...espiration.html

Evidence of air sacs has also been found in theropods. Studies indicate that fossils of coelurosaurs,[30] ceratosaurs,[27] and the theropods Coelophysis and Aerosteon exhibit evidence of air sacs. Coelophysis, from the late Triassic, is one of the earliest dinosaurs whose fossils show evidence of channels for air sacs.[29] Aerosteon, a Late Cretaceous allosaur, had the most bird-like air sacs found so far.[31]


http://en.wikipedia....osaurs#Air_sacs

Turbocharged by environment and design.
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#6 HydrogenBond

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Posted 12 December 2010 - 02:32 PM

I like the idea of replicating red blood cells because of its simplicity. If we started from scratch, evolving an efficient lung system, versus simple red blood cell replication, the red blood cell replication is already up and running almost from the beginning. The other needs time.

In my experience, efficiency shines brighter when there is necessity. For example, during times of plentiful food what is the advantage of an efficient digestive system? A simple behavior change can do the same things as millions of years of evolution. The importance of hardware efficiency will come more into play when the food level drop. At 35% O2, what is the advantage of O2 exchange efficiency? However, when the O2 level fall, the need for efficiency shines brightly.

#7 Turtle

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Posted 12 December 2010 - 05:09 PM

I like the idea of replicating red blood cells because of its simplicity. If we started from scratch, evolving an efficient lung system, versus simple red blood cell replication, the red blood cell replication is already up and running almost from the beginning. The other needs time.

In my experience, efficiency shines brighter when there is necessity. For example, during times of plentiful food what is the advantage of an efficient digestive system? A simple behavior change can do the same things as millions of years of evolution. The importance of hardware efficiency will come more into play when the food level drop. At 35% O2, what is the advantage of O2 exchange efficiency? However, when the O2 level fall, the need for efficiency shines brightly.


let's just set the table straight for you & all the other dear tender readers. your post above - as all your posts - is subterfuge to disguise your metaphysical/theological/religio likeable ideas. other than sharing some words common to science, your post is void of any sensible meaning in the application of the scientific method. as i said before, your intent is always to position science as arbitrary in order to position your "hardware" (i.e. god) as its equal. you have offered no credible links or other support, nor do you ever, nor is there any indication that you intend to. shame on you! :soapbox:

#8 HydrogenBond

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Posted 14 December 2010 - 09:28 AM

I tend to create my own ideas, therefore referencing others may not always be possible. The idea of replicating red blood cells is not metaphysical. One of the challenges faced by science when trying to manufacture red blood cells in the lab was getting rid of the nucleus. It was more natural for these cells to retain their nuclei. That suggested to me that replicating blood cells would have been a more primitive version, with extra features needing to evolve, to rid them of their nucleus. There is also blood doping, where athletes inject their own blood to temporarily increase their blood supply to get additional O2/CO2 exchange for enhanced performance.

Next, I asked myself, say this was to occur, what might happen? For one thing, it would mean more O2/CO2 exchange.

I prefer to work under the assumption of logical explanations, using energy considerations, since even random is not possible unless there is energy to drive the entropy. This is not speculation but is called energy conservation.

For example, say you cooled iron. If we do this quickly we get small crystal size. If we do this slowly crystal size increases. The first releases energy quicker and therefore makes more energy available faster for the higher entropy associated with more crystals. In the case of more O2/CO2 exchange, this means more energy output since we have shifted the energy balance in the direction of the terminal electron acceptor and the removal of terminal products. All the random things which are assumed to drive evolution now have additional energy for entropy, such as cell division. Instead of fewer cells we get more cells. With the red blood cell impact everywhere at the same time, we get an integrated effect.

#9 Turtle

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Posted 14 December 2010 - 04:30 PM

[quotename='Turtle']let's just set the table straight for you & all the other dear tender readers. your post above - as all your posts - is subterfuge to disguise your metaphysical/theological/religio likeable ideas. other than sharing some words common to science, your post is void of any sensible meaning in the application of the scientific method. as i said before, your intent is always to position science as arbitrary in order to position your "hardware" (i.e. god) as its equal. you have offered no credible links or other support, nor do you ever, nor is there any indication that you intend to. shame on you![/quote]

[quote name='HydrogenBond' timestamp='1292340511' post='302803']
I tend to create my own ideas, therefore referencing others may not always be possible. The idea of replicating red blood cells is not metaphysical. One of the challenges faced by science when trying to manufacture red blood cells in the lab was getting rid of the nucleus. It was more natural for these cells to retain their nuclei. That suggested to me that replicating blood cells would have been a more primitive version, with extra features needing to evolve, to rid them of their nucleus. There is also blood doping, where athletes inject their own blood to temporarily increase their blood supply to get additional O2/CO2 exchange for enhanced performance.

Next, I asked myself, say this was to occur, what might happen? For one thing, it would mean more O2/CO2 exchange.

I prefer to work under the assumption of logical explanations, using energy considerations, since even random is not possible unless there is energy to drive the entropy. This is not speculation but is called energy conservation.

For example, say you cooled iron. If we do this quickly we get small crystal size. If we do this slowly crystal size increases. The first releases energy quicker and therefore makes more energy available faster for the higher entropy associated with more crystals. In the case of more O2/CO2 exchange, this means more energy output since we have shifted the energy balance in the direction of the terminal electron acceptor and the removal of terminal products. All the random things which are assumed to drive evolution now have additional energy for entropy, such as cell division. Instead of fewer cells we get more cells. With the red blood cell impact everywhere at the same time, we get an integrated effect.
[/quote]

that you don't deny my charge is a tacit admission of its veracity. stop trashing our board with this duplicitous crapulence. :naughty:
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#10 Rade

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Posted 14 December 2010 - 09:16 PM

The idea of replicating red blood cells would add something similar to a turbo or supercharger effect, where more O2 exchange can occur at metabolism.

No, the situation would be the exact opposite. The energy required for RBC replication would negate the supercharger effect. There are no examples of RBC that replicate in any modern vertebrate, and there is absolutely no reason to expect extinct species found any adaptive value to have individual RBC replicate while they carry O2 within capillaries.

for any DNA, adding red cell replication will supercharge it.

No, this is incorrect. RBC replication is already regulated within bone and spleen. The vertebrate body already has a feedback mechanism to increase RBC numbers, having each individual RBC undergo mitosis would result in the death of the species.

I would guess that the replicating red blood cells would be self limiting. Their own O2 rich state, which allows them to absorb O2 beyond their own needs, means the terminal electron acceptor concentration in their metabolism would shift to the oxidation side of the equation, making it harder to store food or energy value for replication. The blood would need to be rich in food value to compensate, thereby making sure the rest of the cells get their fill before we could expand the red blood cell supply.

Regulation of RBC replication is controlled by hormones. The most efficient way to make sure tissue cells get enough O2 is to have the RBC replication process localized in bone and spleen in vertebrates.

I am looking at the energy side of the equation of life.

OK, then you should realize that it takes energy to replicate DNA via mitosis [and it takes space that could be used by hemoglobin molecules], which consumes O2 via respiration. Any reduction in the O2 carrying capacity of RBCs by replacing hemoglobin molecules with molecules needed for mitosis would result in a pathological condition called anemia. There is no selective advantage for a species to have anemia, which they would if each individual RBC spent energy replicating rather than carry O2.

with a supercharger effect, even the DNA sees an increases in energy input which is conducive to mistakes such as mutations. Stages of evolution with diversity explosion benefits by extra energy.

DNA does not see an increase in energy input if RBC would replicate, DNA does not use O2 directly, O2 is used in the Krebs Cycle to help produce ATP molecules. Stages of evolution do not benefit from extra energy in the individuals of the species. Species do not evolve because they reach a point in time when they have more energy.

With the extra boost of energy to the DNA, we also the have the R&D conditions for the future of selective advantage.

There is no extra boost of energy to DNA required. What limits how much O2 a RBC can carry is the number of hemoglobin molecules/RBC. An example of an anemia brought about by insufficient number of hemoglobin molecules/RBC is called thalassemia. Any attempt to add replication process to a RBC would result in thalassemia because the process would reduce the number of hemoglobin molecules/RBC. There is no energetic or genetic advantage to a species if each individual RBC undergoes mitosis, it can only lead to death of the species.
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#11 Rade

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Posted 14 December 2010 - 10:03 PM

I like the idea of replicating red blood cells because of its simplicity. If we started from scratch, evolving an efficient lung system, versus simple red blood cell replication, the red blood cell replication is already up and running almost from the beginning. The other needs time.

You are confusing how the individual gets O2 from its environment into tissue fluid (gills, lungs, direct through skin)with how the O2 is moved most efficiently around the body so that the O2 reaches all tissue cells. There are amphibians that have neither lungs nor gills as adults, and they do not have RBC that replicate while moving in capillaries. If you start from scratch and have neither lungs nor gills to use for your design, you do not need to have RBC undergo mitosis.

A simple behavior change can do the same things as millions of years of evolution.

A simple behavior change cannot be passed to the offspring. Given a changing environment, within a small number of generations, those individuals with an behavior that has a genetic basis can become common in a population if the behavior is adaptive.
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#12 Turtle

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Posted 14 December 2010 - 11:30 PM

...DNA does not see an increase in energy input if RBC would replicate, DNA does not use O2 directly, O2 is used in the Krebs Cycle to help produce ATP molecules. Stages of evolution do not benefit from extra energy in the individuals of the species. Species do not evolve because they reach a point in time when they have more energy.


thanks for the reply rade. very informative. :thumbs_up. unfortunately, such replies are part of what has me so pissed about h-bond's posting as he will ignore it & reply with yet another inane post. his "point in time' is when god decides to do it, and he has pulled this bs before in inumerable threads on evolution and i find it all a smirch on hypog's integrity not to mention how misleading it is to a young person with a genuine interest in whatever topic gets h-bond's treatment.

this is not a misunderstanding by hydrogen-bond of what science has taught us, this is intentional obfuscation meant to discredit science and promote religious beliefs. while many of you may be content to let it slide with a wink & a nod, i am not of that frame of mind. not a snow ball's chance in hell. :evil:
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#13 HydrogenBond

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Posted 16 December 2010 - 10:02 PM

Species do not evolve because they reach a point in time when they have more energy.


If you look at a cell, it needs to gain energy value (stored food value), so it has the energy potential needed to drive the cell cycle.

If you plot the potential energy of a cell, the cell needs to climb an energy hill; gain stored food value. Once it reaches the top of this potential energy curve, the cell become more proportionally exothermic transforming the stored energy into additional useable energy such as ATP. It slides down the energy curve all the way to two daughter cells. The two daughter cells separate or combined will have less energy than the mother cell, since energy was used up.Each daughter needs to start their climb.

In the case of an ovum, it first climbs its energy hill which is much higher than most cells. After being fertilized, it drops down the other side of the energy curve in steps, with each step one of the cellular divisions, until it bottoms out the energy curve, after the last step. To do anything further, it needs energy input so each of the cells can begin to climb up their energy hills.

If you look at enzymes, they follow the same basic schema. The reactants need to climb an energy hill and go over the other side. The impact of enzymes is to lower the height of the energy hill relative to the reactants without the enzyme.

If we go back into time, it is not a far reach to assume that enzymes were less efficient in the past. That means the energy hill for their enzymatic chemical reactions were higher. Evolution allowed the height of these energy hills to drop; increases in efficiency.

Say you had a modern cell with 50% less efficiency in its enzymes, just to use an average number. The enzyme energy hills will be higher for each reaction, compared to modern efficiency. Relative to the cell, the overall energy curve for cell cycles will be higher, to compensate for the wasted energy that is going to occur. Lack of efficiency at the DNA means not all reactions will work, unless we crank up the energy input so we get a higher yield. The higher level of waste energy will be absorbed by the local water, with equilibrium on the DNA more conducive to mistakes. Perfect base pairing is at at lower energy than mistakes, since mistakes reflect an increase in hydrogen bonding potential. Evolution is tied to energy.

Red blood cells that could replicate would have their unique energy hills. Say we were to remove the nucleus. The cell might attempt to climb an energy hill, but if it attempts to go down the other side, the cascade of reactions that need to occur, to reach the normal bottom, can not occur without the DNA. It will remain at higher energy. Red blood cells that could divide are able to go up and down their energy hills, averaging less energy over time. For some reason, higher average energy red blood cells was evolutionary. The lower energy replicating red blood cells can approximate this by means of larger numbers, to average the energy potential of the blood, closer to the modern higher energy RBC.

#14 Rade

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Posted 17 December 2010 - 02:57 AM

If we go back into time, it is not a far reach to assume that enzymes were less efficient in the past. That means the energy hill for their enzymatic chemical reactions were higher. Evolution allowed the height of these energy hills to drop; increases in efficiency.

Well, no, it would be the exact opposite. If anything, enzymes would be more efficient if you go back in time because mutations would tend to make enzymes less efficient over time. Evolution does not allow the energy hills to drop, it constrains how far the energy hill will rise due to random mutations in the amino acid sequences that form each enzyme.

Lack of efficiency at the DNA means not all reactions will work, unless we crank up the energy input so we get a higher yield. The higher level of waste energy will be absorbed by the local water, with equilibrium on the DNA more conducive to mistakes. Perfect base pairing is at at lower energy than mistakes, since mistakes reflect an increase in hydrogen bonding potential. Evolution is tied to energy.

No. Enzyme efficiency is not determined by the DNA in the cell, but by other factors such as the substrate concentration, pH, etc. Now, DNA does contain the code to form the more than 4000 known biochemical enzymes. All living things require energy to survive and reproduce and enzymes are critical to the production of ATP energy. All living things have potential to evolve over time in response to a changing environment. Living things need energy to reproduce, evolution requires reproduction of genotypes over time (this is what evolution means = change in gene frequency over time in a reproducing population).

Red blood cells that could replicate would have their unique energy hills.

But, no such RBC are known to exist in any vertebrate species. Many non mammal vertebrates have RBC with a nucleus, but the replication process has been shut down. If, as you say, having RBC that could replicate while moving in capillaries was adaptive, I would expect at least some evidence of it in modern vertebrates, but none exists. There is nothing wrong with presenting new hypothesis, but it must be based on some facts concerning modern RBC (some of which have nucleus, others do not). The bottom line is that animals can reach very large size without RBC that reproduce.
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#15 Rade

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Posted 17 December 2010 - 03:00 AM

this is not a misunderstanding by hydrogen-bond of what science has taught us, this is intentional obfuscation meant to discredit science and promote religious beliefs. while many of you may be content to let it slide with a wink & a nod, i am not of that frame of mind. not a snow ball's chance in hell.

What are the options other than ban HB from the forum ?

#16 HydrogenBond

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Posted 17 December 2010 - 10:51 AM

There is nothing wrong with presenting new hypothesis, but it must be based on some facts concerning modern RBC (some of which have nucleus, others do not).


If some species have red blood cells with nuclei, the proof is half way there. This is rare because the evolutionary push was to remove the nucleus. Maybe the question should be why remove the nucleus from RBC's? What is the advantage to making sure red blood cell can not reproduce? What would happen if they could?

I understand the philosophical problem. So much banks on the genetic material being the central random hub of gradual change. If red blood cells were to reproduce, there would be a major change in the internal environment (external cellular blood environment) which would be seen by all cells, at the same time, in an integrated way. The blood supply density around each body system would create its own proportional change simply by means of circulation volume. Natural selection, at the cell level, would then imply a push for change but all at the same time. The cause and effect would then be replicating RBC is the cause, and the final steady state global summation of genetic change the effect.

I am not married to this, but thought it would be interesting to ponder.

#17 Rade

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Posted 17 December 2010 - 02:34 PM

Maybe the question should be why remove the nucleus from RBC's? What is the advantage to making sure red blood cell can not reproduce? What would happen if they could?

HB, I have discussed this. It gets to the question of why RBCs came to be in the first place ? What was the selective advantage to having respiratory pigment (mostly hemoglobin) placed into discrete packages (RBC) to carry O2 to the many tissue cells ? Invertebrates do not have RBC, the O2 is carried directly by pigments within the blood fluid.

The evidence is that primitive vertebrate RBC did have a nucleus. This is expected because stem cells that would form RBC would have a nucleus. I would suspect that very, very early in the evolution of RBC there was a test situation where they did undergo mitosis, and the forms of life with such a trait would have become extinct. Why ? Because it is not the purpose or function of RBC to reproduce, its function is to carry O2 by attaching to hemoglobin molecules. Thus, there would have been strong selective pressure for those individuals with a mutation that shut-down RBC mitosis to survive and reproduce, as opposed to those species that did not carry this mutation.

I understand the philosophical problem. So much banks on the genetic material being the central random hub of gradual change.

The significant change was from no RBCs in invertebrates to having RBCs in vertebrates. Consider the importance of this single structural change in how O2 is transported. The issue of RBC loss of ability to reproduce is relatively easy to explain. Much more interesting for me is how and why RBC come to be in the first place. RBC and the first primitive vertebrate species appear simultaneously in evolution history of animals. We need to look to embryology research to understand how. For example, see these reviews:

http://icb.oxfordjou.../2/189.full.pdf
http://www.scienceda...80210145839.htm
http://www.scienceda...00601072632.htm