That entire system involves changes in the nutrition of the baby as well as a completely new way for the mother to provide the nutrition to the baby. It also requires a separate system of blood transmission which does not have oxygen in it and a complete separation of the blood of the infant from that of the mother. It is obvious that all the changes necessary for this to happen could not have happened stochastically in a single generation. (from:
Post# 257 )-me-
in summary, gore3000's "big change" points #1-#2 represent *minor* modifications of systems which are *already* present in egg-laying species, #3-#4 represent *no* change -- it's hardly an oversimplification to say that the only major steps necessary to convert from an egg-layer to a placental animal is to a) lose the shell, and b) slap the existing chorioallantoic membrane against the uterine wall:
While your detailing of live birth in sharks and other species is very interesting, for the sake of brevity, I shall not discuss it here since not even evolutionists would claim that mammals descended from sharks. You will also note that I will not have any need to insult you since the facts speak for themselves.
According to you all that is needed for a change from egg laying is to get rid of the egg shell and attach the baby to the uterus and there you are! A complete change in mode of reproduction. Problem is that science tells us it is not that easy.
IMPLANTATION:
When considering the fact that in any given menstrual cycle, healthy couples who have intercourse regularly without the use of contraception only have a 25 to 30 percent chance of beginning a pregnancy [1], that only 70 to 75 percent of blastocysts created are able to implant and that only 58 percent of the blastocysts that implant survive past the second week of gestation [2], one comes to understand the miracle of reproduction.
From: Fetal Death
About 6 days after fertilization, the embryo is shaped like a sphere. The surface of the sphere is made up of a layer of specialized cells called the trophoblast. At this phase of development, the embryo is called the blastocyst. The trophoblast later gives rise to the cells that will form the fetus\x{2019} part of the placenta. (The placenta is made up of both maternal and fetal tissues.) The trophoblast is coated with a protein known as L-selectin. The wall of the uterus is coated with carbohydrate molecules. The researchers believe that as the blastocyst travels along the uterine wall, L-selectin on its surface binds to the carbohydrates on the uterine wall, until the blastocyst gradually slows to a complete stop. After this happens, the cells that later become the fetus\x{2019} contribution to the placenta develop. The placental tissue from the fetus then invades the uterine wall by sending finger-like extensions into it. These projections make contact with the maternal blood supply, becoming the pipeline through which the fetus derives nutrients and oxygen, and rids itself of carbon dioxide and wastes.
...
The researchers found that the amount of carbohydrate on the uterine wall was greatest at the time when uterine receptivity to the blastocyst was greatest.
From: Researchers Discover How The Embryo Attaches to the Uterus
Implantation is regulated by a complex interplay between trophoblasts and endometrium. On the one hand trophoblasts have a potent invasive capacity and if allowed to invade unchecked, would spread throughout the uterus. The endometrium, on the other hand, controls trophoblast invasion by secreting locally acting factors (cytokines and protease inhibitors), which modulate trophoblast invasion. Ultimately, normal implantation and placentation is a balance between regulatory gradients created by both the trophoblasts and endometrium (Figure 4).
Figure 4. Regulation of trophoblast invasion by an hCG gradient. Within the placenta the syncytiotrophoblasts generate high levels of hCG which shifts cytotrophoblast differentiation towards a non-invasive hormone secreting villous-type trophoblast. The closer the trophoblasts are to the endometrium the less hCG is made, allowing the trophoblasts to differentiate into anchoring type cells which make the placental glue protein trophouteronectin. Trophoblasts that leave the placenta and migrate within the endo and myometrium are induced to make proteases and protease inhibitors, presumably to facilitate trophoblast invasion into the maternal tissues.
From: Implantation
Without the above happening - with the cooperation of both the baby and the mother, there will be no pregnancy and no reproduction.
THE PLACENTA
Eggs of course do not have a placenta. Without it though, mammalian reproduction would be impossible. There is a quite a bit necessary for a placenta to do its job:
The placenta is the link between a fetus and its mother about the exchange of substances and the thermoregulation. At the childbirth it will be replaced by digestive system, lungs and kidneys of the newborn, for the exchange of substances.
The thermoregulation will be driven by the central nervous system through the control of the blood circulation and of the metabolism.
Other placental functions:
* Production of hormones
* Transmission of chemical messages
* Regulation of the resistances of the fetal circulation
* Regulation of oxygenation of the fetal blood.
How and how much these functions are achieved is still mainly unknown.
The proper perfusion of the placental vessels is a prerequisite for the complete growth of the fetus.
From: Physiology of Fetoplacental Circulation
Does not seem like something you can just say 'abracadabra' and arise by random chance!
At birth there has to be a complete change from blood circulation through the mother to circulation through the baby, this includes a complete switch in the lung function of the baby from its being a consumer of oxygen to an acquirer of oxygen:
In the fetus, the systemic, pulmonary and umbilical circulations have several links. The umbilical and placental circulations are a temporary system for the life and the growth of the fetus, that is abandoned at the childbirth, when drastic changes take place transferring the function of gas exchange from the placenta to the lungs.
Above right - Fetal Circulation in Sheep, Above left - Changes in the Circulation from the fetus to the newborn and adult
From: Fetal Circulation
Does not seem like it could have happened with a single mutation does it?
The transfer of blood requires a very complex system:
we can classify the placental vessels as follows:
+ chorionic vessels;
+ vessels of the cotyledons;
+ capillary vessels in the villi;
+ paravascular capillary network.
The villi can be classified in 5 main groups: stem villi, mature and immature intermediate villi, terminal villi and to mesenchimal villi [20].
From: Anatomy of the Fetal Side
Amazing what can be done with a single mutation eh!
CHANGES IN THE MOTHER:
Human placental lactogen (hPL) is a potent glycoprotein made throughout gestation, increasing progressively until the 36th week, where it can be found in the maternal serum at a concentration of 5-15 µg/ml, the highest concentration of any known protein hormone. The major source of hPL appears to be the villous syncytiotrophoblasts, where it is made at a constant level throughout gestation. In addition to the villous syncytiotrophoblast, hPL has been identified in invasive trophoblasts during the first trimester. hPL appears to regulate the lipid and carbohydrate metabolism of the mother (Figure 14). Placental researchers have also demonstrated by immunohistochemical studies that villous syncytiotrophoblasts contain prolactin, relaxin and chorionic adrenocorticotropin, an ACTH-like protein. The physiological role of placental ACTH is unclear, but as with other placental hormones, all of these hormones may represent a shift from maternal to placental control.
From: Formation of the early Placneta
Amazing what little is needed to change from egg laying to live bearing - just a complete change in the mother!
IMMUNOLOGICAL REJECTION PROBLEMS:
In spite of the fact that the placenta and fetus are foreign to the mother, most pregnancies show no evidence of immunologic rejection. When immunologic reactions do occur, they can be against any of the components of the gestation (placenta and fetus). These reactions can occur at all stages of pregnancy, and can occur repeatedly, pregnancy after pregnancy.
...
In approximately 1-2% of all gestations, mononuclear cells can be seen infiltrating into the chorionic villi of the placenta. Until the work of Redline and Patterson, however, the origin of these cells had been controversial, some arguing for a fetal origin, some for a maternal origin. Since immunochemistry alone could not answer this question they utilized in situ hybridization for Y and X markers in male gestations to demonstrate that the lymphocytes present in cases of chronic villitis are maternally derived, allowing us to focus on the causes of this apparent maternal immunologic reaction against trophoblast and/or villous antigens. Immunohistochemistry of such cases has shown that the cells within the villous core are T-cells and macrophages.
Occasionally placentas manifest an intervillous space that is filled with mononuclear cells. When immunohistochemically stained, these cells are revealed to be monocytic/macrophage in origin. This monocytic intervillositis has been associated with IUGR, preeclampsia, recurrent pregnancy loss and intrauterine fetal demise.
From: Immunological Rejection
Of course the above problem had to be solved before a single baby was born since immunological rejection causes loss of pregnancy.
THE AMNIOTIC SAC
One of the purposes of the amniotic sac is to prevent immunological problems with the mother:
since the bag of waters prevents bacteria from entering the uterus by acting as a barrier, membranes aren't usually ruptured until delivery is imminent.
From: Amniotomy
The amniotic fluid plays an important part in the baby's development:
What is amniotic fluid?
Amniotic fluid is the stuff that surrounds your baby as he grows in the amniotic sac in your uterus during pregnancy, and it serves some important purposes. It cushions your baby against trauma (if you fall down, for example) and keeps the umbilical cord from being compressed (which can reduce your baby's oxygen supply). It protects both the baby and the uterus from infection, provides a zero gravity environment for the baby to move around in, and helps the baby's digestive, musculoskeletal, and breathing systems develop properly.
Where does it come from?
During the first 16 weeks of gestation, the placenta, the amniotic membranes, the umbilical cord, and the baby's skin all produce fluid to fill the amniotic sac as the fetus grows. After that, the fetus starts to swallow the fluid, pass it through his kidneys, and excrete it back out as urine, which he then swallows, recycling the full volume of fluid every few hours. (Yes, that means most of the fluid is eventually urine.) He also excretes some fluid from his lungs. And small amounts are either absorbed by the amniotic sac and diffused into the mother's body or sent back to the mother through the blood in the umbilical cord. Thus, the fetus plays an important role in keeping just the right amount of fluid in the amniotic sac. When there's too little it's called oligohydramnios; when there's too much, it's called hydramnios or polyhydramnios.
From: Pregnancy complications
Seems the amniotic sac is a pretty essential part of the baby's excretory system.
THE UMBILICAL CORD
The umbilical cord is of course essential in this whole process. It is not as simple as one would think:
The umbilical cord normally contains two umbilical arteries and one umbilical vein. These are embedded within a loose, proteoglycan rich matrix known as Wharton's jelly (Figure 5). This jelly has physical properties much like a polyurethane pillow, which if you have ever tried twisting such a pillow you know is resistent to twisting and compression. This property serves to protect the critical vascular lifeline between the placenta and fetus (Figure 6).
Less commonly, but with potentially devastating consequences,the umbilical cord can become knotted (Figure 8). If the knot is loose, fetal circulation is maintained. However, if the knot is tightened, for example at the time of fetal descent through the birth canal, the tightening knot can occlude the circulation between the placenta and fetus, resulting in an intrauterine demise. The Wharton's jelly surrounding the fetal vessels is capable of withstanding significant torsional and compressional forces, as shown in Figure 9. Occasionally, however, Wharton's jelly does not develop in all portions of the cord. When this occurs, the fetal vessels are no longer protected from torsional forces and they can become occluded if twisted sufficiently (Figure 10), again leading to an intrauterine demise.
From: The Umbilical Cord
Seems that the jelly around the umbilical cord is quite necessary. Even with the strong service Wharton's jelly provides in preventing knotting, babies die because of the cutting off of the blood supply.
CONCLUSIONS:
Seems we need quite a lot to happen for this transformation! Even the individual processes within the system which are necessary to accomplish the change over are quite complex and could not have arisen as a result of a single mutation. Further, all the processes are interrelated. The separation of the umbilical cord has to signal a changeover to breathing by lungs and blood circulation wholly within the baby. The joining of the baby to the uterine wall starts the signaling of changes in the mother. In fact, the whole process can be seen as a very careful interaction between the baby and the mother.
As a result of all the above, I think it should be pretty clear to those who have an open mind that at no point is there a possibility that the changes necessary to achieve a transformation of the reproductive system from egg laying to mammalian live birth can be achieved in a single generation. There are way too many changes needed to make a claim that all these changes could have occurred in any sort of gradual manner and that they are far too many to have occurred suddenly in a stochastic manner.
Wow, I'm impressed with your ability to cut-and-paste pages worth of stuff from biological websites. Oh, wait, no I'm not.
You can't make up in volume what you lack in substance. Your points will stand or fall on their own (or is that the problem?) If you feel that you need to support a point, a URL is sufficient to provide a link for further reading. And if you can't put something into your own words, perhaps you don't understand it well enough to use it.
Now on with the show...
As I've long said, properly understanding something is the first requisite of having a chance of actually rebutting it.
Unfortunately, you clearly did not understand my post. Please go back and reread it now before you repeat the mistakes you make here, keeping in mind the following highlights:
1. Contrary to your claim, the egg-laying to placental transition NEED NOT have happened in "one generation". The reason is:
2. As the hammerhead shark method of gestation makes entirely clear, it's perfectly workable to have placental feeding IN ADDITION TO egg-style yolk-feeding of the embryo. Thus:
3. Rather than needing to do the "switchover" in, as you preposterously claim, "one generation", what you have overlooked is the mechanism of: A) start with egg-based yolk-feeding. B) Over however many generations it takes, *add* placental feeding to yolk-feeding. C) Over however many generations it takes, phase out yolk-feeding and leave placental feeding as the primary embryonic nutrition source.
Thus, you were flatly wrong when you declared that there was no "gradualistic" way to transition from one to the other, because there *is* a workable, *gradualistic* pathway which you failed to consider as a possibility. QED.
As a sidebar issue, note that:
4. I don't need to demonstrate that it *did* happen that way, since that wasn't the claim being examined. The claim was *your* claim that it *couldn't* happen in *any* gradualistic way, period. In order to prove you wrong, I only need to demonstrate a *workable* gradualistic pathway that you had overlooked which allowed multi-generational change to occur without "breaking" the system. I did that.
And:
5. Evolution isn't even on the table here, since you claimed to have ruled out any "gradualistic" development BY ANY METHOD -- and my counterexample works as a gradualistic development method NO MATTER WHAT DRIVES IT.
Now let's look over your response...
While your detailing of live birth in sharks and other species is very interesting, for the sake of brevity, I shall not discuss it here since not even evolutionists would claim that mammals descended from sharks.
Boggle... Did you actually not understand the point being made there, or are you just trying to misrepresent what I actually said in the hopes anyone will swallow it? Or perhaps you're just trolling.
Hint: "Descent" wasn't relevant to the point being made, nor did I in any way claim that it was, or that descent was even involved.
Hint #2: It was a good point, and your dodging of it doesn't help your case any. You can't weaken a point by closing your eyes and hoping it'll go away. An honest debater would concede the point, or rebut it head-on.
According to you all that is needed for a change from egg laying is to get rid of the egg shell and attach the baby to the uterus and there you are!
I said those were the only "major" steps necessary, yeah.
A complete change in mode of reproduction.
I spent several thousand words explaining in detail why you were wrong when you claimed it was a "complete change" in the method of reproduction -- did you not bother to read it?
Problem is that science tells us it is not that easy.
To borrow an old phrase, you use science the way a drunk uses a lamppost -- for support instead of illumination. You frequently argue against science and scientific methods when it suits you, but then you aren't shy about digging frantically for "scientific" support when your own concepts start eroding.
Ok, let's look at what you've got...
[biology primer cut-and-paste snipped]
Without the above happening - with the cooperation of both the baby and the mother, there will be no pregnancy and no reproduction.
Some of it yes, some of it no (for example, the interdigitation limiters aren't necessary for non-deciduate placentas, so they're hardly a necessary "starter feature").
But you're just trying to muddy the waters. That in no way invalidates any of the points I made in my post to you, nor repairs any of the multiple flaws in your original erroneous claim.
See point #3 above: Retention of the yolk-feeding method allows "gradualism" however long it takes to cobble together a combination of changes which enables the first successful placenta. It's not true that th ere would be "no pregnancy and no reproduction" until all the changes were in place, since the *pre-existing* reproduction method would work just fine until a new method became workable.
Did you not understand post #378?
Eggs of course do not have a placenta. Without it though, mammalian reproduction would be impossible.
Wrong again. As I pointed out in my post #378 (you *did* read it, didn't you?) marsupials don't have placentas (most of them, anyway) and yet their "mammalian reproduction" is, obviously, not "impossible".
Furthermore, *again* as I showed in my post #378 (try *reading* it before you try to rebut it, please), eggs actually *do* have "placentas" in a sense -- the extraembryonic tissues that allow an embryo to develop successfully in an egg are the *same* structures that make placentas workable.
Are you ignoring these issues, or just pretending to? Neither option inspires confidence...
There is a quite a bit necessary for a placenta to do its job:
[Cut-and-paste says:] The placenta is the link between a fetus and its mother about the exchange of substances and the thermoregulation. At the childbirth it will be replaced by digestive system, lungs and kidneys of the newborn, for the exchange of substances. The thermoregulation will be driven by the central nervous system through the control of the blood circulation and of the metabolism.
...all of which is the case for egg-hatched reproduction as well. So much for requiring a "change"...
[Cut-and-paste says:] Other placental functions: * Production of hormones * Transmission of chemical messages * Regulation of the resistances of the fetal circulation * Regulation of oxygenation of the fetal blood. How and how much these functions are achieved is still mainly unknown.
...all of which are refinements to the reproductive process which were made possible after primitive placental birth was developed, and are not necessary requirements for the first appearance of placental feeding. Immaterial to the argument, which I shouldn't have to remind you, is about whether placentas could *first* arise *at all*.
The proper perfusion of the placental vessels is a prerequisite for the complete growth of the fetus. From: Physiology of Fetoplacental Circulation
Again, if you had *read* my post #378, you'd see examples demonstrating that "complete" growth of the fetus is not a necessary function of the first placenta in order for it to be highly useful. Some marsupials are examples of this.
Does not seem like something you can just say 'abracadabra' and arise by random chance!
Straw man. It happened neither by "abracadabra", nor by "random chance" acting alone. NOR is a Darwinian origin even at issue here, refer back to point #5 above if you're still unclear on that point. You're wrong even *apart* from any argument about Darwinian evolution as a method.
At birth there has to be a complete change from blood circulation through the mother to circulation through the baby,
Horse manure, fetal blood circulation is *never* "through the mother". From the start, the embryo has its *own*, *self-contained* blood system.
this includes a complete switch in the lung function of the baby from its being a consumer of oxygen to an acquirer of oxygen:
Gee, just like in a hatching egg... Again, no change necessary there. And again, just as I had *already* pointed out in post #378. Try understanding it next time.
[cut-and-paste says:] In the fetus, the systemic, pulmonary and umbilical circulations have several links. The umbilical and placental circulations are a temporary system for the life and the growth of the fetus, that is abandoned at the childbirth, when drastic changes take place transferring the function of gas exchange from the placenta to the lungs.
Gee, again, just like *also* happens in an animal hatching out of an egg. *Again*, no change necessary there. I covered this already -- do you need a refresher course?
Does not seem like it could have happened with a single mutation does it?
Sigh. There you go with your "single mutation" fetish again. See point #3 above.
Furthermore, I again refer you to the fact that the "switchovers" you focus on are *already* present and working in egg-hatched species. So they hardly have to be added by *any* number of mutations in order to be put into identical service for placental birth.
The transfer of blood requires a very complex system:
Again you are in error -- there is no "transfer of blood".
[Cut-and-paste says:] we can classify the placental vessels as follows: + chorionic vessels; + vessels of the cotyledons; + capillary vessels in the villi; + paravascular capillary network. The villi can be classified in 5 main groups: stem villi, mature and immature intermediate villi, terminal villi and to mesenchimal villi [20]. From: Anatomy of the Fetal Side
Again, all present in egg-hatched vertebrates, except for the final branches of the villi, and while those increase efficiency, they aren't necessary for the success of a primitive placenta.
Amazing what can be done with a single mutation eh!
Amazing how stubbornly you stick to the "single mutation" fallacy.
Nothing requires the changes to be a "single mutation" (nor in a "single generation"), nor do most of your alleged "changes" actually need to happen at all, because they *aren't* "changes" -- they are features and mechanisms *already* present in egg-hatched species.
But then, this was already explained to you in post #378. What's your excuse for not understanding it?
CHANGES IN THE MOTHER:
[cut-and-paste snipped]
Amazing what little is needed to change from egg laying to live bearing - just a complete change in the mother!
Sorry, but none of that is required for a primitive placental gestation. They can be added as refinements after the initial system is in place.
And the production of a few hormones is hardly a "complete change in the mother", so don't overstate the issue.
IMMUNOLOGICAL REJECTION PROBLEMS:
[Cut-and-paste snipped]
Of course the above problem had to be solved before a single baby was born since immunological rejection causes loss of pregnancy.
You really need to try reading your own sources before you offer them in alleged support of your claims. Your quoted material says no such thing. It only says that rejection sometimes occurs, *not* that there's a special system in place which "solves" the problem and that rejection would invariably occur without it.
Furthermore, it's clear that egg-hatched species already have immunosuppressive systems, since sperm cells are not rejected on their way to the ovum, and the fertilized ovum (which is likewise "foreign" to the mother) is not rejected as it passes down the birth canal and gets built into an egg.
One of the purposes of the amniotic sac is to prevent immunological problems with the mother:
[Cut-and-paste says:] since the bag of waters prevents bacteria from entering the uterus by acting as a barrier, membranes aren't usually ruptured until delivery is imminent.
That's sweet, but irrelevant, since eggs have amniotic sacs too.
Yet again, I must ask you to learn something about egg-laying as a method of reproduction before you make a fool of yourself declaring what might or might not be a big "change" when compared to placental birth.
The amniotic fluid plays an important part in the baby's development:
[Cut-and-paste snipped]
Seems the amniotic sac is a pretty essential part of the baby's excretory system.
Yup. Sure is. Just like it is in eggs, too. Yet again, you might want to learn something about it before you make yet another mistake about what does and does not need to be added/changed in order to go from eggs to placentas...
The umbilical cord is of course essential in this whole process. It is not as simple as one would think:
[cut-and-paste snipped]
Seems that the jelly around the umbilical cord is quite necessary. Even with the strong service Wharton's jelly provides in preventing knotting, babies die because of the cutting off of the blood supply.
Yup, sure is. By the way, eggs have umbilical cords and take care to prevent twisting as well...
CONCLUSIONS:
Seems we need quite a lot to happen for this transformation!
"Seems" not after all, once we snip out all the parts of your long list that a) are *already* present in eggs, thus requiring no "transformation", and b) weren't necessary for the first placenta but were later improvements.
In fact, gosh, once you take out all that hand-waving, we're left with the issues I already covered in my post #378. Amazing.
Even the individual processes within the system which are necessary to accomplish the change over are quite complex and could not have arisen as a result of a single mutation.
Big whoop-de-doo, since as I already spelled out in great detail in post #378, they need not happen in "a single mutation", nor "a single generation. Reread point #3 above if you're still unclear on this concept. Or hell, reread post #378, I already covered this.
So... Did you not read post #378 before you attempted to rebut it, or did you not understand it, or are you purposely avoiding the parts of it that you know cause problems for your claim? Inquiring minds want to know.
Further, all the processes are interrelated. The separation of the umbilical cord has to signal a changeover to breathing by lungs and blood circulation wholly within the baby.
Already present in egg-layers, fella.
The joining of the baby to the uterine wall starts the signaling of changes in the mother. In fact, the whole process can be seen as a very careful interaction between the baby and the mother.
Not necessary for the first placenta, although later development of such coordination certainly improves the system.
As a result of all the above, I think it should be pretty clear to those who have an open mind that at no point is there a possibility that the changes necessary to achieve a transformation of the reproductive system from egg laying to mammalian live birth can be achieved in a single generation.
"Single generation", eh? You're a broken record. Reread point #3 above, and post #378. WE ALREADY COVERED THAT. So why do you lamely pretend that we haven't?
There are way too many changes needed to make a claim that all these changes could have occurred in any sort of gradual manner
...so you claim, without actually making a case for it. All your arguments so far have been of the faulty "one mutation, one generation" variety. If you're going to shift gears now and insist that gradual change is ruled out, you're going to have to prove *why*. If you're going to try that now, be very sure that you're working on a *minimal* set of *necessary* changes, and *not* a laundry-list of *modern* features which are not only more advanced than any likely first placenta, but are even more advanced than many other mammalian placentas (e.g. cows). Good luck.
and that they are far too many to have occurred suddenly in a stochastic manner.
They didn't, nor did they need to, which is exactly why you were dead wrong in your post #257, and why you would be well advised to just admit that you were wrong and retract it rather than bluster on.