Your points will stand or fall on their own (or is that the problem?) Indeed it is a problem. The problem is that the differences detailed between egg-laying and live bearing animals are individual only for purposes of detailing, but they very much form a system which requires all the parts to work together:
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. -me-
Not necessary for the first placenta, although later development of such coordination certainly improves the system.
The above is the evolutionist 'leap of faith' through a chasm the size of the Grand Canyon. The only purpose of a placenta is the transfer of nutrients from the mother to the baby through the uterine wall. This alone requires both changes in the uterine wall of the mother, the attachment of the placenta to the uterine wall, and the non-rejection of the 'foreign' body by the mother. This by itself requires numerous changes in the growing baby and the mother as well as numerous specific proteins to be secreted to achieve a successful change in nutritional system. As the following shows:
The mammalian embryo obtains nutrients directly from its mother and does not rely on stored yolk. This adaptation has entailed a dramatic restructuring of the maternal anatomy (such as expansion of the oviduct to form the uterus) as well as the development of a fetal organ capable of absorbing maternal nutrients. This fetal organ ---the chorion ---is derived primarily from embryonic trophoblast cells, supplemented with mesodermal cells derived from the inner cell mass. The chorion forms the fetal portion of the placenta. It will induce the uterine cells to form the maternal portion of the placenta, the decidua. The decidua becomes rich in the blood vessels that will provide oxygen and nutrients to the embryo.
From: Modifications for Development within Another Organism
Let's look at the above problem more closely:
While the embryonic epiblast is undergoing cell movements reminiscent of those seen in reptilian or avian gastrulation, the extraembryonic cells are making the distinctly mammalian tissues that enable the fetus to survive within the maternal uterus. Although the initial trophoblast cells of mice and humans divide like most other cells of the body, they give rise to a population of cells wherein nuclear division occurs in the absence of cytokinesis. The original type of trophoblast cells constitute a layer called the cytotrophoblast, whereas the multinucleated type of cell forms the syncytiotrophoblast. The cytotrophoblast initially adheres to the endometrium through a series of adhesion molecules. Moreover, these cells also contain proteolytic enzymes that enable them to enter the uterine wall and remodel the uterine blood vessels so that the maternal blood bathes fetal blood vessels. The syncytiotrophoblast tissue is thought to further the progression of the embryo into the uterine wall by digesting uterine tissue (Fisher et al. 1989). The uterus, in turn, sends blood vessels into this area, where they eventually contact the syncytiotrophoblast. Shortly thereafter, mesodermal tissue extends outward from the gastrulating embryo (see Figure 11.27D). Studies of human and rhesus monkey embryos have suggested that the yolk sac (and hence the hypoblast) is the source of this extraembryonic mesoderm (Bianchi et al. 1993). The extraembryonic mesoderm joins the trophoblastic extensions and gives rise to the blood vessels that carry nutrients from the mother to the embryo. The narrow connecting stalk of extraembryonic mesoderm that links the embryo to the trophoblast eventually forms the vessels of the umbilical cord. The fully developed extraembryonic organ, consisting of trophoblast tissue and blood vessel-containing mesoderm, is called the chorion, and it fuses with the uterine wall to create the placenta. Thus, the placenta has both a maternal portion (the uterine endometrium, which is modified during pregnancy) and a fetal component (the chorion). The chorion may be very closely apposed to maternal tissues while still being readily separable from them (as in the contact placenta of the pig), or it may be so intimately integrated with maternal tissues that the two cannot be separated without damage to both the mother and the developing fetus (as in the deciduous placenta of most mammals, including humans).
From: Formation of Extraembryonic Membranes
There are numerous 'little' problems within the above that need to be solved for the system to work properly, one of them is oxygen:
The solution to the fetus's problem of getting oxygen from its mother's blood involves the development of a fetal hemoglobin. The hemoglobin in fetal red blood cells differs slightly from that in adult corpuscles. Two of the four peptides of the fetal and adult hemoglobin chains are identical ---the alpha (α) chains ---but adult hemoglobin has two beta (β) chains, while the fetus has two gamma (γ) chains (Figure 15.11). Normal β-chains bind the natural regulator diphosphoglycerate, which assists in the unloading of oxygen. The γ-chain isoforms do not bind diphosphoglycerate as well and therefore have a higher affinity for oxygen. in the low-oxygen environment of the placenta, oxygen is released from adult hemoglobin. in this same environment, fetal hemoglobin does not give away oxygen, but binds it. This small difference in oxygen affinity mediates the transfer of oxygen from the mother to the fetus. Within the fetus, the myoglobin of the fetal muscles has an even higher affinity for oxygen, so oxygen molecules pass from fetal hemoglobin for storage and use in the fetal muscles. Fetal hemoglobin is not deleterious to the newborn, and in humans, the replacement of fetal hemoglobin-containing blood cells with adult hemoglobin-containing blood cells is not complete until about 6 months after birth.
From: Fetal Hemoglobyn
I could go on and on, however, let's just show the problem of adhesion:
The mouse blastocyst hatches from the zona by lysing a small hole in it and squeezing through that hole as the blastocyst expands (Figure 11.25). A trypsin-like protease, strypsin, is located on the trophoblast cell membranes and lyses a hole in the fibrillar matrix of the zona (Perona and Wassarman 1986; Yamazaki and Kato 1989). Once out, the blastocyst can make direct contact with the uterus. The uterine epithelium (endometrium) “catches” the blastocyst on an extracellular matrix containing collagen, laminin, fibronectin, hyaluronic acid, and heparan sulfate receptors. The trophoblast cells contain integrins that will bind to the uterine collagen, fibronectin, and laminin, and they synthesize heparan sulfate proteoglycan precisely prior to implantation (see Carson et al. 1993). Once in contact with the endometrium, the trophoblast secretes another set of proteases, including collagenase, stromelysin, and plasminogen activator. These protein-digesting enzymes digest the extracellular matrix of the uterine tissue, enabling the blastocyst to bury itself within the uterine wall (Strickland et al. 1976; Brenner et al. 1989).
Implantation
Finally, lets show the developmental system of an egg:
This is a picture of a 4 day quail embryo. It is on the yolk with the some of the egg shell removed. Notice the large vessels which are required to provide the nutrients necessary for the rapid development if the embryo. The heart and eye are evident by somewhat obscured by the presence of a new membrane structure, the allantois. The allantois grows from the umbilicus (belly button) and has two primary functions. First it is a waste storage area for the embryo and it will be the gas exchange organ while the embryo is confined in the egg. After hatching, the chick will leave the allantois in the shell. The heart is the red structure in the middle of the embryo and the eye is visible as a dark area in the head.
Compare the above to the picture of the human developmental system in Post# 257 .
Again, each step requires numerous other steps as well as coordination of all the steps. The reductionism of evolutionists does not cut it. The steps are numerous and have to be precisely timed, they need various genes, proteins and organs.
The problem is that the differences detailed between egg-laying and live bearing animals are individual only for purposes of detailing, but they very much form a system which requires all the parts to work together: You're dodging again. When I point out specific problems in your claims, you dodge and shift to grandiose generalities. When I point out the problems with your generalities, you dodge by xeroxing page after page of vaguely related minutiae from various websites.
You clearly love dancing, but since you keep stepping on your own feet, let's turn off the music and cut to the chase.
Your original claim was that "gradualistic" development of placental birth from an egg-laying predecessor was "impossible" because it couldn't have happened in "one mutation" or "one generation". You asserted that it *must* have happened "all at once" (or else not at all) because otherwise the embryo would have "starved" for lack of nourishment.
I demolished this on several grounds.
First, I showed that you had completely overlooked the mechanism of developing placental feeding *in addition to* the pre-existent yolk-feeding method, not as an immediate *replacement* for it to which you had simplistically limited your thinking. This opens the door for a *multi-generational* development of the placenta instead of the "single generation" method you had considered to be the "only" possibility.
To date, you have not attempted to refute that point at all. Nor, unfortunately, have you conceded it. Instead, you've just danced around it hoping to distract attention from it by reprinting pages of various websites for us, while *continuing* to cling to your flawed "one mutation, one generation" scenario.
Second, you have grasped for as much as you can get your hands on (including the aforementioned spews of website cut-and-pastes) and flung it against the wall in the hopes that something sticks. Your hope was that you could find something that would show that a placenta is (allegedly) so much more complex than egg-laying mechanisms that its development would boggle the mind (well, *your* mind, anyway).
Unfortunately, all of your specific examples have so far fallen into the following categories:
1. Structures or processes *already present* in egg-hatched reproduction. Sorry, no cigar, since these hardly need to be "developed" in order to be put into service for placental birth.
2. Structures or processes which clearly are not necessary for a primitive placenta, they are merely improvements (albeit sometimes great improvements) on the minimum configuration, and could be added at any later point after the "first" successful placenta was developed. I include in this category those structures/processes which you simply *declare* to be absolutely necessary but for which you have not provided any sort of actual evidence. *You're* the one making the claim of impossibility, *you* document the alleged impossibilities and demonstrate that they are, indeed, absolutely necessary steps. You have the burden of proof.
3. Structures or processes which may have been necessary novel developments for the first primitive placenta, which you claim (without any real support) are somehow impossibly difficult. See #2 for a discussion of your responsibility for a burden of proof. I'm afraid that your just saying, "gosh-a-roony, that sure looks hard to me" doesn't even begin to approach the standards of actual evidence.
And as a further flavor of error in your argument:
4. We haven't even yet touched on the topic of your presumptions of "irreducible complexity". For example, the placenta could have started out as something else useful before it became useful as a nutritional conduit. For just one scenario, it may first have served as just an "anchor" to the womb while the embryo subsisted off its yolk prior to early (e.g. marsupial-like) birth. Only many generations later, once it was already reliably attaching to the uterine wall, might it have developed a way to pass nutrients. I don't think this is necessarily what happened, but the point is that in order to actually cover all bases in your "can't get there from here" claims, you need to make sure you've considered and examined *every* possible series of stages, and then eliminated each and every one of them. Otherwise, your claims are just empty declarations, devoid of any real rigorous support.
The above is the evolutionist 'leap of faith' through a chasm the size of the Grand Canyon.
No, sorry, *you're* the one claiming that it *couldn't* have worked without *all* modern features in place. *You're* the one making a "leap of faith" if you haven't already examined and discredited *every* possible pathway by which one could get to "here" from "there". My job in this discussion is simply to point out all the possibilities you clearly *hadn't* already considered.
The only purpose of a placenta is the transfer of nutrients from the mother to the baby through the uterine wall. This alone requires both changes in the uterine wall of the mother,
Oh? Prove it. Prove that the embryo-side of the placenta couldn't "leech" enough nutrients out of an *unmodified* uterine wall to be at least partially useful (especially since this is pretty much how the ruminant placenta works *now*). Until you have proven this, you *can't* claim that you've made your case. Admit it -- you're operating off of feelings, without evidence (and until I informed you of a great deal and corrected your many errors, without any real knowledge of how the whole system actually works).
the attachment of the placenta to the uterine wall,
Hardly a major feat, due to point #1 above ("already works that way in eggs").
and the non-rejection of the 'foreign' body by the mother.
We already dealt with that in a prior post, don't pretend we haven't. That problem would already have been addressed long before placental development commenced.
Furthermore, it's clear that rejection isn't automatic failure for gestation, since equine (horse) gestation *always* involves immunilogical rejection of the "chorionic girdle" which develops at about 25 days into gestation, and becomes completely rejected by the mother at about day 100-140. But no matter, since by then it has already done its job. Didn't know that, did you?
This by itself requires numerous changes in the growing baby and the mother as well as numerous specific proteins to be secreted to achieve a successful change in nutritional system.
In *modern* placentas. Do get back to us when you show that they were a necessary component of the *first* eutherian placenta. For elucidation you might want to do some research and find out how many of them *aren't* present in the perfectly workable shark and marsupial placentas.
Ooh, better yet, let's compare your account to *other* eutherian mammalian placentas to see how much of that is actually "necessary", shall we?
Ruminant (cows, sheep, etc.) placentas work in a pretty straightforward manner, much simpler than human placentas which you erroneously focus on as if they were the *only* workable kind.
The uterine wall of the ruminant undergoes essentially *no* changes in preparation for the attachment of the placenta. The placenta nestles up to wavy tissues of the uterus which are *always* present in the ruminant uterus, pregant or not. It just plasters up against the uterine wall as it grows and doesn't do any kind of "invasion". And it doesn't do any of the fancy "coordination" you believe is necessary for a functioning placenta. Oops.
As the following shows:
[cut-and-paste snipped]
Um, it "shows" nothing of the kind, you might want to read your own sources more carefully. Note the following passage, "It will induce the uterine cells to form the maternal portion of the placenta, the decidua". See the mention of the "decidua"? This is discussing only *deciduate* placentas. Guess what? Ruminant placentas work just fine *without* all this rigamarole. So much for your presumption that this mechanism is a necessary ingredient of primitive placentas, eh? Oops again.
Let's look at the above problem more closely:
Let's not, since cows get along just fine without all that overcomplication.
[Cut-and-paste says:] While the embryonic epiblast is undergoing cell movements reminiscent of those seen in reptilian or avian gastrulation,
*AHEM*... Free clue for the clueless -- and from your own sources, too...
There are numerous 'little' problems within the above that need to be solved for the system to work properly, one of them is oxygen:
Why is this a "problem"? Sure, having a fetal hemoglobin with a higher oxygen affinity than the maternal hemoglobin increases the efficiency of the transfer, but can you demonstrate that it's *necessary*? Some lemurs, for example, appear to use the same hemoglobin throughout both their fetal and post-birth lives. Even theoretically, oxygen transfer would still take place with identical hemoglobins on both sides of the placental barrier, just not as efficiently.
But even if were actually a necessity before placentas became feasible, it's hardly an insurmountable step. A proliferation of hemoglobin types is the norm among animals, not the exception. For all you know, birds and reptiles may very well already use a fetal hemoglobin during the egg stage, where respiration is performed quite differently than during "post hatch" life (I wasn't able to find any specific information either way on that).
I could go on and on,
Oh, I'm sure you could... But wouldn't it be simpler to just admit holes in your original faulty claim? Like, say, admitting that it *needn't* have happened in "one generation" after all?
however, let's just show the problem of adhesion: [Implantation]
Cows don't bother with any of that and they work just fine... How many more times am I going to have to instruct you on basic biology?
Finally, lets show the developmental system of an egg: [picture snipped] Compare the above to the picture of the human developmental system in Post# 257 .
Looks pretty much the same to me -- did you have a point to make? And, by the way, it *really* looks like the intra-uterine cow embryo.
Again, each step requires numerous other steps as well as coordination of all the steps.
Again, cows do fine with about 3/4 fewer steps than you have listed as "essential". Try again.
The reductionism of evolutionists does not cut it.
And yet, cows still live... Maybe it's your assumptions that are wrong.
The steps are numerous and have to be precisely timed, they need various genes, proteins and organs.
Mooooooooooooo!
I'm going to summarize with the statement I used to start this whole discussion -- if you were smart, you'd have made sure that you actually *knew* enough about gestation to be able to discuss it intelligently and not trip over something that's already known, like for example how other animals already manage to reproduce.
Now that I've dealt with your latest round of "throw another website at the wall and hope something sticks", let's get back to basics...
Do you admit that your original presumption that it "had" to occur "in one mutation, in one generation" was faulty? Yes or no.
Do you admit that you erred when you presumed that mammals would have had to "develop" structures and processes which, oops, were already present in the egg-laying method of reproduction? Yes or no.
Do you withdraw your original claim that gradualistic development of placental birth would be "impossible"? Yes or no.
Note: This is a test of your intelligence and honesty. Respond accordingly.