Clues To Ancestral Origin Of Placenta Emerge In Genetics Study

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While ID proponents have spent much time on a ‘documentary’ which misrepresents science, the scientific community and fails to present any scientifically relevant explanations related to the concept of Intelligent Design, real scientists have been working hard to unravel another mystery: the origin and evolution of the placenta

In a paper titled Genomic evolution of the placenta using co-option and duplication and divergence researchers Kirstin Knox and Julie C. Baker (soon to be published in Genome Research) describe how they have started to unravel the mystery of the placenta

The invention of the placenta facilitated the evolution of mammals. How the placenta evolved from the simple structure observed in birds and reptiles into the complex organ that sustains human life is one of the great mysteries of evolution. By using a timecourse microarray analysis including the entire lifetime of the placenta, we uncover molecular and genomic changes that underlie placentation and find that two distinct evolutionary mechanisms were utilized during placental evolution in mice and human. Ancient genes involved in growth and metabolism were co-opted for use during early embryogenesis, likely enabling the accelerated development of extraembryonic tissues. Recently duplicated genes are utilized at later stages of placentation to meet the metabolic needs of a diverse range of pregnancy physiologies. Together, these mechanisms served to develop the specialized placenta, a novel structure that led to expansion of the eutherian mammal, including humankind.

In Clues To Ancestral Origin Of Placenta Emerge In Genetics Study” ScienceDaily describes the relevance of these findings:

The evidence suggests the placenta of humans and other mammals evolved from the much simpler tissue that attached to the inside of eggshells and enabled the embryos of our distant ancestors, the birds and reptiles, to get oxygen.

Remind me again, how does ID explain the origin/evolution of the placenta?

Sigh…

63 Comments

Remind me again, how does ID explain the origin/evolution of the placenta?

Oh, I wouldn’t put stork in them having much of an explanation…

Henry

Bye Bye troll

Charlemage:

There is nothing in that paper that proves the religion of evolutionism. If human placentas evolve from egg shell linings in birds by random chance, then why don’t human placentas evolve every time you fry an egg? You add energy to the chicken egg, so why doesn’t the evolution happen every day at the breakfast table?!

PvM:

Bye Bye troll

Charlemage:

There is nothing in that paper that proves the religion of evolutionism. If human placentas evolve from egg shell linings in birds by random chance, then why don’t human placentas evolve every time you fry an egg? You add energy to the chicken egg, so why doesn’t the evolution happen every day at the breakfast table?!

Thats just truly sad

Charlemage logic matches up with www.youtube.com/watch?v=FZFG5PKw504

The invention of the placenta facilitated the evolution of mammals

Queue up the UD crowd: “But inventions have inventors!!11!1!1!!!”

PvM:

Bye Bye troll

Charlemage:

There is nothing in that paper that proves the religion of evolutionism. If human placentas evolve from egg shell linings in birds by random chance, then why don’t human placentas evolve every time you fry an egg? You add energy to the chicken egg, so why doesn’t the evolution happen every day at the breakfast table?!

If Charlemage ever bothered to learn elementary biology or even zoology, he would realize that human placenta would have more in common with a monotreme’s egg (such as that of an echidna), than a chicken’s egg, if only because humans are more closely related to echidnas, than they are to chickens. Plus, Charlemage would have already realized that the mammalian placenta is derived from the membranous structures of the typical amniote egg, in that, instead of anchoring the embryo to the lining the inside of the eggshell, and providing gas exchange with the outside without dehydrating, the egg’s membranes now provide an attachment to the internal surface of the uterus, and provide a means of gas- and nutrient exchange with the mother, as well as to protect the fetus/embryo from the mother’s immune system.

So, these same mechanisms, (gene duplication followed by divergence and then elaboration of regulatory functions and developmental pathways), hve been responsible for many novel evolutionary features, including hemoglobin, feathers, placentas, etc. The mechanisms of gene duplication are well understood and the mechanisms of divergence are well understood. We are also beginning to understand the mechnisms that allow for the evolution of gene regulation and changes in developmental pathways as well. Once again, Darwin’s dangerous idea has been dramatically confirmed. Seems that the God of the gaps just keeps getting smaller and smaller.

Perhaps it would be better to embrace the science rather than whine about the supposed “moral implications”. Otherwise, when the science becomes so overwhelming and undeniable, people might just remember the moral behavior of those who tried to deny the science and forget that science still can’t make any moral decisions for you.

David Stanton:

Perhaps it would be better to embrace the science rather than whine about the supposed “moral implications”. Otherwise, when the science becomes so overwhelming and undeniable, people might just remember the moral behavior of those who tried to deny the science and forget that science still can’t make any moral decisions for you.

Personally, I prefer to think of the “moral implications” of Darwin’s dangerous idea to be along the lines of “expanding one’s understanding of life is a good thing in and of itself, but if it can be used to benefit others, it’s even better.”

The placenta has evolved at least twice. There is a group of ancient animals called placental sharks.

One source claims that reproductive strategies are evolutionarily malleable. Some sharks, fish, snakes, lizards, ichthyosaurs and mosasaurs, use live birth while some mammals lay eggs.

Article Evolution and morphogenesis of the placenta in sharks William C. Hamlett Department of Anatomy, Medical College of Ohio, Toledo, Ohio 43699

Abstract Placental sharks sequentially utilize three modes of embryonic/fetal nutrition to nourish their developing young - viz., vitellogenesis, histotroph secretion, and hematrophic placentation. These are the principal modes employed by vertebrates in general. The progressive shift from reliance on yolk, to histotroph, then to the placenta mirrors the probable stages in the evolution of placentation in sharks. Preimplantation shark embryos begin their ontogenetic development by reliance on yolk. In vitellogenesis, energy-rich precursors of hepatic origin are stored in oocytes prior to ovulation. Following fertilization, embryogenesis and fetal development proceed at the expense of the yolk stores sequestered in the yolk sac. Yolk is made available to the developing young by two means. Yolk is partially solubilized in the yolk syncytium of the yolk sac and subsequently modulated through the yolk sac endoderm. Yolk metabolites are then transported across the vitelline endothelium to reach the fetal circulation. Yolk granules are physically transported to the fetal gut by ciliated cells lining the ductus vitellointestinalis. The ductus is an endodermally lined conduit that extends from the yolk sac to connect to the fetal gut where digestion and absorption occur. Following depletion of the yolk stores and prior to development of the placenta, nutrient substances may be supplied to the fetus by secretory activity of the uterus in the form of histotroph. Histotroph may then be ingested and/or absorbed. In the transition from the yolk-reliant and histotrophic phases to a placental situation, there is a coincident shift in the function of the maternal uterus to one of a nutrient-producing or -transporting organ. Essential adaptations of the uterus include: enhanced secretory function, expansion to accommodate the embryos, respiration, osmoregulation, waste disposal, and protection of the young. As the yolk sac differentiates into a placenta, focal areas of the uterus become modified as uterine attachment sites. It is at the utero-placental complex that nutrient and metabolic exchange between mother and fetus will be effected. Paraplacental uterine sites may also continue to play a role in the elaboration of histotroph. The placenta is specialized into two segments: a proximal, smooth portion that has characteristics of a steroid-producing tissue and a more richly vascularized distal portion that is a nutrient-transporting tissue. Evolution of placentation involves modifications of existing maternal and fetal membranes. The ontogenetic transformation of the shark oviduct into a functional uterus for the retention and metabolic support of developing young certainly is modulated by endocrine regulation. In the developing fetus, the yolk sac and stalk display terminal differentiation into a regionally specialized placenta and an umbilical cord respectively. Accessory vascular structures of the umbilical cord, termed appendiculae, are present in some species.

Females that lay eggs are oviparous (monotremes, birds, and most reptiles, amphibians and fish). Some reptiles and fish retain the eggs in the body, hatch them inside, and give birth to hatched young (“ovoviviparous”). However, in some cases the young are retained inside the female and start to be nourished from the mother’s bloodstream. This involves the development of a placenta. That seems like a very complex affair, but we see independently developed placentas at various stages of development in placental mammals, wombat-koala marsupials, a bunch of snakes and lizards, and some fish.

Thompson et al. (1) refer to viviparity evolving in over 100 separate lineages within lizards and snakes. Most of their placenta are comparatively simple (see here, #2), but at least one is in some ways comparable to the mammalian placenta in its complexity (here, #3)

Just to cite a few examples in fish, although there are many more, in sharks, the bull shark, whitetip reef shark, lemon shark, blue shark, mako, porbeagle, salmon shark, the silvertip shark, the Hammerhead, and the whale shark have placentas.

Also, the topminnow offers a particularly interesting set of examples. Specifically, Reznick et al. (in Science, 2002, #4) studied placenta development in topminnows (Poeciliopsis).

The evolution of complex organs is a source of controversy because they require the contributions of many adaptations to function properly. We argue that placentas are complex, that they have evolved multiple times in Poeciliopsis, and that there are closely related sister taxa that have either no placentas or intermediate stages in the evolution of a placenta. Furthermore, placentas can evolve in 750,000 years or less, on the same time scale as suggested for by theoretical calculations for the evolution of complex eyes. Independent origins of such complexity, accompanied by sister taxa that either lack or have intermediate stages in the evolution of the trait, present an opportunity to study the evolution of novelty and complexity from a comparative, evolutionary perspective.

My links don’t seem to be working in preview, so here they are. 1 = www.bio.usyd.edu.au/staff/thommo/pdfs/2004/139ThompsonAdamsHerbertBiazikMurphy2004.pdf

2 = http://icb.oxfordjournals.org/cgi/c[…]act/32/2/303

3 = http://www.pubmedcentral.gov/articl[…]artid=391591

4 = http://www.bec.ucla.edu/papers/Rezn[…]_1-24-05.pdf

Now that we live in pretty good shelters that keep wild animals away from our young … can we go back to laying eggs please? :-)

Stacy S.:

Now that we live in pretty good shelters that keep wild animals away from our young … can we go back to laying eggs please? :-)

I do understand your wish that is shared by many females.

Please, allow some nitpicking. What do you mean by “wild animals”, as compared to … what?

Regards

Eric

Eric Finn:

Stacy S.:

Now that we live in pretty good shelters that keep wild animals away from our young … can we go back to laying eggs please? :-)

I do understand your wish that is shared by many females.

Please, allow some nitpicking. What do you mean by “wild animals”, as compared to … what?

Regards

Eric

As in actual predatory animals, such as large eagles, wolves, jackals, lions, tigers, and bears that would seize and feed upon the young of other animals, including those of humans.

Stanton, do you think that wolves are “wilder” than rabbits?

Stanton:

Eric Finn: Please, allow some nitpicking. What do you mean by “wild animals”, as compared to … what?

As in actual predatory animals, such as large eagles, wolves, jackals, lions, tigers, and bears that would seize and feed upon the young of other animals, including those of humans.

Regards

Eric

Eric Finn:

Stanton, do you think that wolves are “wilder” than rabbits?

Tell me, moron, which is more likely to attack and eat an unguarded five-year old child, a wolf, or a rabbit?

Stanton:

Eric Finn:

Stanton, do you think that wolves are “wilder” than rabbits?

Tell me, moron, which is more likely to attack and eat an unguarded five-year old child, a wolf, or a rabbit?

I do not know the reason you are attacking every post I make, apart from me being a moron.

Panda’s thumb has been a great asset for me, not only by providing information, but also providing me an opportunity to discuss items that puzzle me.

Stanton, if your aim is to stop me posting on this site, you are very close to achieving that goal.

Regards

Eric

Depends on the rabbit:

http://www.youtube.com/watch?v=XcxKIJTb3Hg

Perhaps a little levity will ease the tension…

As a parent of an egg, I wouldn’t be concerned about a bunny eating my offspring. True. Unless it were the Evil Easter Bunny.

Not the first time someone has wished that humans were egg layers rather than viviparous. This thought frequently occurs in maternity wards.

There was some talk of developing an artificial womb a while ago. With advances in artificial organs and reconstructive medicine, it might be possible someday. The tissues of the placenta and the membranes are derived from the embryo, not the mother, parts of the ancient shelled egg exaptated.

My idea was to reengineer walking wombs such as cows to support human development. Embryos can sometimes be transferred between related species with successful development.

Many of your comments sound like those a concern-troll creationist would make, especially your comment about how the Theory of Evolution is incomplete because it does not proscribe behavior like a religion, and that you ask painfully obvious questions, like questioning about wild animals and young children, despite the fact that there is a monstrously huge source of literature about the dangers of mixing wild animals with children, as well as the myriad examples (re: literally true horror stories) of how wild animals will bite, eat, scratch, claw, sting, and pass disease and parasites to young children.

Forgive me if I sound cruel, but, I don’t care to restrain myself around people who make light or appear to make light of mixing wild animals with children, especially when I keep hearing horror stories like when a woman set out to get a picture of her son being kissed by one of the bears in Yellowstone, only to have him be mauled to death when she lured a bear into kissing her son by smearing his cheek with jam.

If you aren’t a troll, I apologize: instincts die hard.

Eric Finn:

Stanton:

Eric Finn:

Stanton, do you think that wolves are “wilder” than rabbits?

Tell me, moron, which is more likely to attack and eat an unguarded five-year old child, a wolf, or a rabbit?

I do not know the reason you are attacking every post I make, apart from me being a moron.

Panda’s thumb has been a great asset for me, not only by providing information, but also providing me an opportunity to discuss items that puzzle me.

Stanton, if your aim is to stop me posting on this site, you are very close to achieving that goal.

Regards

Eric

Depends on the rabbit:

Where’s Elmer Fudd when ya need ‘em… :p

Henry

From the article:

They found that the placenta develops in two distinct stages. In the first stage, which runs from the beginning of pregnancy through mid-gestation, the placental cells primarily activate genes that mammals have in common with birds and reptiles. This suggests that the placenta initially evolved through repurposing genes the early mammals inherited from their immediate ancestors when they arose more than 120 million years ago. In the second stage, cells of the mammalian placenta switch to a new wave of species-specific genes. Mice activate newly evolved mouse genes and humans activate human genes.

For those of you interested in thinking logically, let’s break this down. There are two types of ideas in this paragraph: facts, and “suggestions.” The facts are that all most of the genes activated during the first stage are common to mammals, birds, and reptiles; and during the second half, mice activate genes unique to mice, and humans activate genes unique to humans.

This is science, and absolutely fascinating.

The “suggestion” is that because similar genes common to several species are activated during the first stage, they are “ancient” genes.

This is not science. It’s speculation, premised on the assumption of common descent, and with absolutely no evidence, novel or otherwise, to support it.

By analogy, a hybrid vehicle and a model T both have tires made of rubber (something in common), and things not in common (the unique design of their engine). The inference to evolution is like saying, “Well, because we know that hybrids and model T’s are related, we can conclude that tires are ancient and inherited by both.”

That’s an absurd inference.

The real challenge here is to understand how those genes came to work together in coordination – is there a feasible stepwise pattern from “no placenta” to “protoplacenta” to “mammalian placenta?”

Not yet. Quite the contrary, it looks like there’s a sudden switch from universal genes (all of which are still inexplicably coordinated) to species-species genes (all of which are also still inexplicably coordinated). Like noticing that certain elements of different computer models are shared, and certain elements are radically, uniquely, different in a highly coordinated manner.

That inference is also not science. It’s an inference. It’s the design inference. But it’s just as reasonable, if not superior, to the alternative.

The problem with evolutionists is they take perfectly good science, and make ridiculous, unfounded proclamations of “yet more evidence than evolution.” The problem’s not in the science. The problem’s in your interpretation thereof.

ungtss,

Your argument presupposes that every piece of evidence has to support the whole theory all over again. There’s at least a couple of problems with that approach.

1) An already established theory is supported by the totality of the relevant evidence, not any one piece thereof.

2) Once the general principles of a theory are established as being well supported by the evidence, it is quite reasonable to regard those principles as being well supported by the evidence.

Henry

By analogy, a hybrid vehicle and a model T both have tires made of rubber (something in common), and things not in common (the unique design of their engine). The inference to evolution is like saying, “Well, because we know that hybrids and model T’s are related, we can conclude that tires are ancient and inherited by both.”

It seems to me that there are two problems with your analogy. One is that rubber tyres are an ancient feature of cars (in so far as anything is). Secondly, we know that hybrid vehicles and Model T’s are not related in the same way that organisms are because cars do not have babies.

Also, as Henry says, there is massive amounts of data showing the relationships between mammals, birds and reptiles. It would be foolish not to make use of this information.

ungtss:

From the article:

By analogy, a hybrid vehicle and a model T both have tires made of rubber (something in common), and things not in common (the unique design of their engine). The inference to evolution is like saying, “Well, because we know that hybrids and model T’s are related, we can conclude that tires are ancient and inherited by both.”

That’s an absurd inference.

When I worked in engine electronics engineering at Ford, my desk was less than 100 feet from what had been Henry Ford’s old office back when the building was the primary Ford manufacturing facility.

The Model T and any hybrid automobile that contains a gasoline/petrol-powered internal combustion engine may easily be shown to be derived from a common ancestor.

Any two wheeled vehicles may be shown to be derived from a common ancestor; the material used for the wheel-to-road interface (“tyre”) is a contingent detail.

So, yes,

“…tires are ancient and inherited by both.”

Henry J:

ungtss,

Your argument presupposes that every piece of evidence has to support the whole theory all over again. There’s at least a couple of problems with that approach.

1) An already established theory is supported by the totality of the relevant evidence, not any one piece thereof.

2) Once the general principles of a theory are established as being well supported by the evidence, it is quite reasonable to regard those principles as being well supported by the evidence.

Henry

Henry: Thank you for your very thoughtful response. My impression, and the impression of those who think like me, is that the belief that the “totality or relevant evidence” unequivocally supports common descent stems from the same faulty inference.

1) A (usually very interesting) scientific fact is identified;

2) An unfalsifiable, unobservable inference is drawn from the scientific fact, and called “scientific fact.”

3) Nobody argues over the fact. It’s obvious and uncontroversial. But everybody argues over the inference, because it is not obvious, and is enormously controversial.

Early on it came down to sheer physiological similarity: “Humans and apes are physiologically similar. Therefore they are related.” Faulty, obviously. Paradigm-dependent.

Later on it moved on to embryos: “Embryos of diverse species look similar. Therefore they are related.” Faulty, obviously. Also paradigm-dependent.

Lately it’s been all about ERVs: “A tiny minority of the 10s of thousands of ERV-like sequences in the genome appear in identical places in some (not all) humans and some (not all) chimps. Therefore we’re related.” Also faulty. Never mind that we haven’t determined if the ERVs are set in the whole population (which would be a prerequisite to infer common descent) nor that the observed ERVs are known to be capable of infecting both humans and simians independently, nor that the vast majority of the ERV sequences are NOT shared by the humans and simians that have thusfar been sequenced. In fact, the argument comes down to selection bias. Scan the 10,000-some-odd ERVs in both genomes, find 1 or 2 in the same place, and conclude common descent. Don’t bother to check to see if the ERVs are set in the respective populations. Don’t mention that even given independent infection, one or two are bound to end up in the same place given tens of thousands of ERVs.

The observed facts regarding ERVs are clearly consistent with both an evolutionary scenario and an ID scenario.

And now it’s the fact that diverse species use similar proteins early in placental development. Therefore we’re related. That’s faulty. If we were to genetically engineer life forms to colonize another planet, we would ABSOLUTELY use similar designs in diverse species. Computer programmers do that today, borrowing and tweaking subroutines, then plugging them into wildly different software packages. Why shouldn’t we expect similar mechanisms for placental development.

It all comes down to that same inference – which is philosophical in nature, not scientific. Nobody’s arguing about the facts in front of us. We’re all arguing about interpretations of facts that cannot, by their very nature, be directly observed.

Shebardigan:

Any two wheeled vehicles may be shown to be derived from a common ancestor; the material used for the wheel-to-road interface (“tyre”) is a contingent detail.

Error: wheeled transport (apparently) evolved independently in multiple locations, although in North/South America it was strictly limited to toys.

So, what we see here is a case of convergent evolution.

So sorry.

So, yes,

“…tires are ancient and inherited by both.”

remains apposite natheless.

Any two wheeled vehicles may be shown to be derived from a common ancestor; the material used for the wheel-to-road interface (“tyre”) is a contingent detail.

Automobile “lineages” have often borrowed innovations developed in other “lineages” of technology, such as computers, lights, seat belts, refined metals, plastics (and maybe even internal combustion engines as well; I don’t recall for what those were originally developed, but I strongly suspect it wasn’t cars). Technology doesn’t follow the strict nested hierarchy expected of species that evolve without swapping significant amounts of DNA between species. That limits the usefulness of the analogy. Plus, unless there’s an explanation as to why the bioengineer(s) didn’t reuse already developed technology outside of the taxon in which it was developed, the biology as technology argument actually works against the notion that the details of life on Earth were deliberately engineered.

Faulty, obviously. Paradigm-dependent.

But that goes right back to what I said earlier, which I’ll paraphrase here: if a principle has already been established as being supported by evidence, it makes no sense to have to reinvent that principle for a new piece of evidence.

What supports a theory is the patterns that occur repeatedly and consistently throughout the relevant evidence, of which nested hierarchy is perhaps the most important. There’s also divergence of types over time, lack of types that don’t fit in the heirarchy, geographic clustering of close relatives (at least with types that aren’t globally mobile). On a side note, as I understand it, the geographic clustering was what initially caused Darwin to reach his conclusion.

Without details on what “Intelligent Design” actually says (those do seem to be in short supply), with the simplest interpretation of “life was deliberately engineered” I would expected there to be massive exceptions to all of those patterns (e.g., frequent sharing of technology outside the taxon in which it originally appeared, geographic redistribution of derived species, species that don’t fit the hierarchy, DNA differences that don’t fit the hierarchy, maybe even species showing up long before several of their presumed predecessors.)

Henry

Shebardigan:

ungtss:

From the article:

By analogy, a hybrid vehicle and a model T both have tires made of rubber (something in common), and things not in common (the unique design of their engine). The inference to evolution is like saying, “Well, because we know that hybrids and model T’s are related, we can conclude that tires are ancient and inherited by both.”

That’s an absurd inference.

When I worked in engine electronics engineering at Ford, my desk was less than 100 feet from what had been Henry Ford’s old office back when the building was the primary Ford manufacturing facility.

The Model T and any hybrid automobile that contains a gasoline/petrol-powered internal combustion engine may easily be shown to be derived from a common ancestor.

Any two wheeled vehicles may be shown to be derived from a common ancestor; the material used for the wheel-to-road interface (“tyre”) is a contingent detail.

So, yes,

“…tires are ancient and inherited by both.”

You are using “inherited” in two radically different senses. What you mean, literally, is that the ideas were reused by intelligent designers. Not that cars bred.

Henry J:

What supports a theory is the patterns that occur repeatedly and consistently throughout the relevant evidence, of which nested hierarchy is perhaps the most important. There’s also divergence of types over time, lack of types that don’t fit in the heirarchy, geographic clustering of close relatives (at least with types that aren’t globally mobile). On a side note, as I understand it, the geographic clustering was what initially caused Darwin to reach his conclusion.

Without details on what “Intelligent Design” actually says (those do seem to be in short supply), with the simplest interpretation of “life was deliberately engineered” I would expected there to be massive exceptions to all of those patterns (e.g., frequent sharing of technology outside the taxon in which it originally appeared, geographic redistribution of derived species, species that don’t fit the hierarchy, DNA differences that don’t fit the hierarchy, maybe even species showing up long before several of their presumed predecessors.)

Henry: Thank you again for your thoughtful response.

You characterize exceptions to nested hierarchies as a prediction of ID. Yet vehicles, which are obviously intelligently designed, have nested hierarchies. You have “Vehicle,” “Utility vehicle,” “Pickup,” “Extended cab,” “4WD,” colors, options, etc. It is easy to draw a nested hierarchy of automobiles. That’s why nested hierarchies are consistent with both common descent and ID. You simply impose criteria of commonality, and group according to those criteria. Nested hierarchies are consistent with both ID and common descent.

Now that’s not to say that ID rejects any common descent at all. Rather, ID holds to the principle of genetic entropy – that the dominant function in the history of the diversification of life is the LOSS, rather than the GAIN, of genetic diversity within populations, through natural selection and speciation. Thus a primal “Cat” with the capacity to be both lion and tiger diversified into lion and tiger as it moved into different ecological niches. Thus, rather than a single tree of life which is thin at the bottom and thicker and more robust at the ends of the branches, there are many different trees of life, which branch from thick and robust to thin and niche-dependent.

You characterize exceptions to nested hierarchies as a prediction of ID. Yet vehicles, which are obviously intelligently designed, have nested hierarchies. You have “Vehicle,” “Utility vehicle,” “Pickup,” “Extended cab,” “4WD,” colors, options, etc. It is easy to draw a nested hierarchy of automobiles.

It is indeed. However, if you prepare nested trees based on, say, the spark plugs, the speedometer or the seat covers, you will get different trees. In biology, you would get the same tree.

Initially taxonomic trees of organisms were thought of in just the same way as you could think of them with vehicles. For example, plants were distinguished on whether or not they had seeds, whether the seeds were borne in flowers, whether the seedlings had one cotyledon or two and so on. However, it became apparent that organisms placed in one group had many different features in common and to a large extent it did not matter what features were used, an essentially similar pattern emerged. This, basically, was the stimulus for considering common descent.

These days, data can be collected on all kinds of things, for example the exact distribution of the amino acids in proteins with specific functions. The data are thrown into a computer program that has no idea of what outcome is expected yet the resulting trees conform remarkably closely to trees derived from other data. The results are not as good for plants as animals because genetic material can be transferred from one species to another by diseases. However, for animals I have seen data in which the probability of getting as good a match or better by pure chance was 1 in 10360. It is far more than ‘sheer physical similarity’. When biologists talk about a ‘nested hierarchy’ what they mean is a nested hierarchy that is the same regardless of the traits used (obviously things that are variable or easily change such as animal weight are not considered or are given very little emphasis).

I’ve just seen this comment:

ungtss said:

Wings appear in insects, mammals, birds, and reptiles. While they are all wings, they function in radically different ways. Did all organisms with wings evolve from a common winged ancestor? Or did wings evolve independently in each of these taxa/clades?

The latter, as is easily seen if you look at their structure.

If there was a common winged ancestor, then I guess the earliest mammal was a bat-like creature. But nobody appears to be making that argument. So it would appear that the view of the “scientific community” is that wings evolved independently. That is a violation of the nested heirarchies.

I’ve no idea what you mean here. A ‘violation of a nested hierarchy’ would be if a pigeon had a bat’s wing while a hawk had a bird’s wing.

Sonar/radar also violates this rule. Bats and dolphins have it. So are we to believe that the earliest mammal had it and it atrophied in all mammals but bats and dolphins, or that it evolved independently?

The latter, of course, given that the sound is detected in quite different ways (I don’t know about its production). BTW, it’s sonar, not radar, and it is also used by oilbirds and a blind teenager.

To see an outline of the statistics dealing with taxonomic trees, look at 29+ Evidences for Macroevolution Some Statistics of Incongruent Phylogenetic Trees. Also browse through some recent issues of ‘Science’ for examples of it in practice. I do not have access to it at present so I can’t refer to specific papers but there is usually something on the topic.

As to the “DNA being totally different,” that’s not what nested hierarchies are based on – nested hierarchies are based on gross anatomical characteristics.

Why do you say this? Nested hierarchies can be based on detailed (not so much gross) anatomical characteristics. They can also be based on the DNA. Or if you wish you could base one on cytochrome C. The fundamental point, though, is that each of these hierarchies will be essentially the same.

Then how do you know which traits exhibit homology, and which exhibit homoplasy?

By paying more attention to the aspects of the structure that have little effect on the function. For example, although several groups of animals can fly, they have quite different structures to achieve it. Birds have a wing with a reduced number of fused digits and feathers produce the wing area. Bats have skin stretched between elongated digits and their rear legs, pterodactyls had a single elongated digit.

Suppose I assume that internal or external birth are fundamental. The hierarchy starts to look different. Yet it seems to me that’s a much more fundamental characteristic than the capacity to produce milk.

But it isn’t. All that is required to change external to internal birth is to delay the time the egg spends in the reproductive tract. Milk production requires glands on the skin that are absent in most animals.

Nothing about the facts necessitates common descent any more than it necessitates a common designer.

The trouble is, it doesn’t look like that a common designer was involved. It looks more like a designer started things off, then subcontracted a group out to another designer, who sub-subcontracted (“OK, here’s a basic marsupial. Take it off to Australia and see what you can do with it. And no cheating by looking to see what’s being done with placentals.”)

Ungtss,

You seem to be under the mistaken impression that biologists are all idiots and are only out to fool you. That is incorrect and illogical. Why would any scientist care what you think?

Homology is determined based on objective criteria. With genes there are statistical tests that can be employed to determine homology. With anatomy, homologous structures must be the same structure coded for by the same genes and produced by the same developmental pathways. Homoplasy in the data is reduced by careful examination of the characters involved BEFORE the clasdistic analysis is performed. We know the mechanisms of mutation and we know the relative and absolute rates of change for molecular characters. We avoid homoplasy by choosing characters that evolve at a rate appropriate to reduce the probability of convergence and reversal. The reasoning is not circular. The nested hierarchy is the result not the assumption.

As for endogenous retroiviruses (ERVs) or SINE insertions, we also know the mechanisms of transposition. There are literally millions of insertion recognition sequences in eukaryotic genomes. The probability of shared insertions by chance alone is extremely low. There is also no known mechanism for reversal, making this the perfect character for phylogenetics. Insertions persist through speciation events, thus shared insertions are strong evidence of common descent (the alternative being that God copied the mistakes). Now here is the important point, insertions are not only shared between species, but they are shared in a particular pattern, they are found in a nested hierarchy! In fact, it is the same hierarchy that is reconstructed by gene sequences, morphological analysis and the fossil record. Check out the Talk Origins archieve on plagarized errors in the Molecular Genetics section.

The nested hierarchy is exactly what is predicted by descent with modification. It is inconsistent with the hypothesis of a designer. If you insist that it is consistent, then you must explain why the designer created exactly the pattern that would be expected from common descent and no other. Is God trying to fool you as well? If so, you better play along, you know how she gets when she’s angry.

Henry,

Thanks for the information. Of course this is just another example of superficial convergence. If the designer was responsible, I’m sure she could have done a much better job.

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This page contains a single entry by PvM published on April 19, 2008 1:02 AM.

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