Posted on 05/20/2006 6:02:56 PM PDT by Al Simmons
Fetus' Feet Show Fish, Reptile Vestiges By Jennifer Viegas, Discovery News
May 18, 2006 — The feet of human embryos taking shape in the womb reveal links to prehistoric fish and reptiles, a new study finds.
Human feet may not look reptilian once babies emerge from the womb, but during development the appendages appear similar to prehistoric fish and reptiles. The finding supports the theory that mammalian feet evolved from ancient mammal-like reptiles that, in turn, evolved from fish.
It also suggests that evolution -- whether that of a species over time or the developmental course of a single organism -- follows distinct patterns.
In this case, the evolution of mammalian feet from fish fins to four-legged reptiles to four-limbed mammals to human feet appears to roughly mirror what happens to a maturing human embryo.
"Undoubtedly there are clear parallels between the mammal-like reptilian foot and the human foot," said Albert Isidro, an anthropologist at the Autonomous University of Barcelona, Spain and lead author of the study, which appeared in the journal The Foot.
Isidro and colleague Teresa Vazquez made the determination after analyzing fossils of a number of mammal-like reptiles that lived from 75 to 360 million years ago. The scientists also studied fossils of osteolepiform fish, which appear to be half fish and half reptilian. These fish lived 400 million years ago and had lungs, nostrils and four fins located where limbs would later be found in four-footed reptiles and mammals.
In 33-day-old human embryos, the scientists observed "the outline of a lower extremity in the form of a fin, similar to that seen in osteolepiform fishes." As the embryo continued to develop, the researchers focused their attention on two foot bones: the calcaneous, or heel bone, and the talus, which sits between the heel and the lower leg.
At 54 days of gestation, these two bones sit next to each other as they did within the reptile herbivore Bauria cynops, which lived around 260 million years ago. This ancient reptile had flat, crushing teeth and mammalian features.
At eight and a half weeks of gestation, the researchers found the two embryonic foot bones resemble those seen in the Diademodon vegetarian dinosaur, which lived around 230 million years ago.
"We can tell that the embryo is half way between the reptiles and the mammals (at this stage)," Isidro told Discovery News.
The two foot bones continue to develop until, at nine weeks, they resemble that of placental mammals as they emerged 80 million years ago.
This development of feet in the human embryo mirrors how the foot evolved over millions of years beginning with fish and ending with early mammals, according to the scientists.
Supporting the fish/foot link was the discovery last month of a new species, Tiktaalik roseae, which lived 375 million years ago. It had fish fins and scales, but also limb parts found in four-legged animals.
"Tiktaalik blurs the boundary between fish and land-living animals both in terms of its anatomy and its way of life," said Neil Shubin, professor and chairman of organismal biology at the University of Chicago and co-author of a related paper in the journal Nature.
H. Richard Lane, director of sedimentary geology and paleobiology at the National Science Foundation, said, "These exciting discoveries are providing fossil ‘Rosetta Stones’ for a deeper understanding of this evolutionary milestone: fish to land-roaming tetrapods (four limbed animals)."
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It seems you are saying this is Haeckelism without the weird mysticism.
And, on the other topic,
The ToE does so
How does the ToE explain them?
<< There is a simple and elegant explanation for the nerve in standard biology. The question is, is there an explanation within creationism r ID. >>
CREATIONISM: Goddune it, I believe it, and that settles it!
ID: Go... oops... the "unknown designer" did it, and we don't know how. Since we don't know how -- NOW -- it must be "irreducibly complex." And if you don't accept this as science, you're just anti-Go... oops.
See? Piece o' cake.
No, Haeckel had a (failed) theory; this research is simply reporting some new facts about embryology.
How does the ToE explain them?
I should have said "standard biology (making heavy use of the ToE) explains them".
1) The marsupian egg shell and egg teeth.
This one's fairly obvious. The ToE claims that mammals arose from reptiles. All reptiles produce eggs with shells, and almost all of them lay eggs. There are a few, however that engage in oviviviparity (ie the eggs hatch inside the mother).
The gestation of a marsupial is very similar to this. So the ToE basically claims that in the line leading up to present-day marsupials, there were egg-laying mammals (like present-day monotremes) that became oviviviparous. This neatly accounts for both the formation and reabsorbtion of the shell and the egg tooth.
2) The migrating ear bones of mammals.
Here's a PDF that goes into great detail about the development of marsupial ossicles.
Whether the condition of the marsupial neonate with regard to the evolution of the ossicles and the mammalian masticatory apparatus can be cited as an example of recapitulation or not depends on how recapitulation is defined. The marsupial condition around the time of birth is neither anatomically nor functionally like that of any living adult sauropsid or purported adult mammalian ancestor (Luo,1994).What is usually called Haeckelian recapitulation (the accuracy of the claim about what Haeckel meant aside) involving the “repetition of adult stages of the ancestor during the ontogeny of the descendant” (e.g., Lovejoy, 2000:356), clearly does not take place. It seems more appropriate in this case to talk about “von Baer’s recapitulation” (Lovejoy, 2000, and references therein), since we hypothesize that the condition of the marsupial neonate resembles that of the embryonic condition of mammalian ancestors.
What's happening here is in accordance with von Baer's laws. The ToE explains this by saying that a mutation to the development of one of the jaw bones led to better hearing. This got fixed in the population (and luckily, some of the animals got fossilized), and allowed for a second mutation that made hearing even better. This process repeated a number of times. The result is that the sequential expression of these mutations during development mimics the fossil record.
3) Recurrent laryngeal nerve.
This is similar to 2), but we have to start from the position of blood vessels and nerves in the early chordates.
I'm not sure though, what it tells us -- how it brings forth a greater understanding of fundamental biological issues except in a very broad conceptual framework -- ie its food for thought, that's all. Fair enough but it is not hard as in cellular respiration takes place in the mitochondria or spatio-temporal expression of homeotic genes are necessary for pattern formation during development to use two random examples (and this second is fairly vague -- or soft in spots -- as well).
And as far as how it reflects on what is called "intelligent design", I'm not sure how it would undercut that or support it, either, at all.
It's a bit more than that. The laryngeal nerve doesn't make sense as design; it does make sense as an artifact of evolution.
Putting its development in the context of chordates, fish, ammphibians, etc, moves it from the just-so category to "facts true of all chordates that need a scientific explanation" category
I'm not sure though, what it tells us -- how it brings forth a greater understanding of fundamental biological issues except in a very broad conceptual framework --
There are few more fundamental issues in biology than the whys and hows of embryonic development. In particular, the study in the original post, and the ones that I and others have linked to, shed light on which parts of the process are common to fish, amphibians, etc, which parts are unique to mammals, and so forth.
I would not be a bit surprised if this sort of research were cited when how to regenerate human limbs is finally worked out.
And as far as how it reflects on what is called "intelligent design", I'm not sure how it would undercut that or support it, either, at all.
There's that extra 15 feet of nerve in the giraffe. I simply can't get my head around the notion that there's anything intelligent in that design.
Why would a designer put in genes for an egg tooth that's never used?
Why did the platypus' designer put in genes for teeth that are never used?
On a visual basis. I give up. I don't know what species they are. Why don't you tell me what each one is and at what point of gestation they're at. And their actual sizes relative to each other.
I will tell you if you guess right. The stages of gestation are similar, although not the same age. Age is irrelevant for this discussion. Living things develop at different rates, even within species.
I don't want to play games. I just want the answer along with the gestation stages of each and the relative sizes. You can freepmail me if you want so it doesn't spoil it for anyone else.
I'm no biologist, and the images came from all over the web, but the stage would be called the pharyngula period or stage. I'm not going to reveal the species until someone gets it right.
My point is that photographs of actual embryos are not that different, to a layman, than the drawings creationists object to.
<< My point is that photographs of actual embryos are not that different, to a layman, than the drawings creationists object to. >>
Maybe Satan faked the embryo evidence the same way he faked the fossil evidence -- to lead us astray.
Or maybe God did it to test our faith.
Or maybe there really are pink unicorns circling Neptune.
And my point is that without comparative points of reference such as relative gestation periods and relative sizes, these photos are worthless for showing how similar embryos are. The pig embryo (if it's still considered an embryo) could be at a much later stage of development (relatively) the the human. Without this reference it seems like it's nothing more than an attempt to make your case by using selective stages that show a superficial similarity.
Or a blue ring around Uranus.
Thanks. Good luck making your point without any evidence that they're honest comparative photographs.
Why the emphasis on the giraffe. It's the same in all mammals isn't it? It's just extra inches in man or others.
I simply can't get my head around the notion that there's anything intelligent in that design.
OK, but that is theology, not biology.
The idea that this nerve syste doesn't make sense -- that there's no reason to have it structured in that manner -- is also something that you simply assume with no evidence to support your assertion.
At this level everything you've said is story telling. It's based on observation and thought and is sound story telling, but is still story telling none the less.
At some levels biology can only still be a soft science ie a story telling science.
It's just a dramatic illustration of stupendously stupid design. Yes, it's the same in all mammals.
In people I guess it's an extra foot, foot and a half, judging by twice the distance from my Adams apple to my heart. Think of large dogs, horses, etc
OK, but that is theology, not biology.
How so? I haven't mentioned God, I've just said some things are too stupid to have been intelligently designed.
To me, it's more of an aesthetic judgment. I wouldn't hire an architect or electrician who ran the wires from the push button by the front door to the bell on the wall behind it via the furnace room.
It violates my sense of tidiness and thriftiness.
The idea that this nerve syste doesn't make sense -- that there's no reason to have it structured in that manner -- is also something that you simply assume with no evidence to support your assertion.
The superior laryngeal nerve takes the direct route. The right hand branch loops around the subclavial artery, and is only about two thirds as long as the left branch
Scroll down past the photo to the digram
Also, if I understand the surgical and anatomical jargon on the surgery websites Google returned correctly, in some people it doesn't take the indirect route at all.
So I'd say there is reason to doubt that it was consciously designed like that.
[story telling]
Which story is more likely to be true:
The nerve follows the indirect path because it inherited it from very distant ancestors (in which the path was direct), OR
the nerve follows this path because it was designed to do so, in spite of the fact that it violates common sense and good engineering practice?
Which story is more likely to be true:
the one that is consistent with the rest of biology, OR
the one that postulates an unknown function for the indirect route simply because it assumes it was designed and assumes the designer was intelligent, and therefore there must be some reason for it?
Think of Occam
You have no evidence whatsoever to support this or any of your other assertions about the stucture of this nerve system.
Opinion isn't science. Ideas of tidiness are not science. Your comments and views actually sound like the arguments made in the pre-Darwinian period in that they emanated not from any experimental evidence but from pre-conceived concepts of what should be right (eg ideas of tidyness) based upon worldview.
Something that has fascinated me of late are the fernlike crystals which form when aminotic fluid is present.
This fact has been used to develop simple at home pregnancy tests over the past ten years.
Does this fernlike pattern hark back to common plant ancestry?
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