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Author
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Topic: Are human tails an example of macroevolution?
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Message 1 of 61 (352993)
09-28-2006 9:24 PM
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Faith claimed in the thread “Origin of new genes” that human tails
aren't much in the way of tails anyway, just a flaccid rope of skin
This is not supported by the facts. Human tails are described in the following
abstract:
A case of a tail in a 2-week-old infant is reported, and findings from a review of 33 previously reported cases of true tails and pseudotails are summarized. The true, or persistent, vestigial tail of humans arises from the most distal remnant of the embryonic tail. It contains adipose and connective tissue, central bundles of striated muscle, blood vessels, and nerves and is covered by skin. Bone, cartilage, notochord, and spinal cord are lacking. The true tail arises by retention of structures found normally in fetal development. It may be as long as 13 cm, can move and contract, and occurs twice as often in males as in females. A true tail is easily removed surgically, without residual effects. It is rarely familial.
There are rare cases where even skeletal structures are developed, as can be seen in this case:
Case 1 . A 10-year-old Arab boy arrived at our Outpatient Department
in 1977 complaining ofpain in the coccygeal region. This had first been
noticed some years previously but had become worse and was
particularly severe when he was sitting on hard surfaces. He was fully
continent of both urine and faeces. There was no history of injury,
operation or illnesses other than those commonly occurring in
childhood.
On examination, he was seen to be a healthy, well-developed
child. Systematic examination was normal and there was no
neurological deficit. On inspection, there was no perineal abnormality
but on rectal examination the posterior bony wall was found to be
markedly flexible and passive movement, particularly of the tip,
caused the patient great discomfort.
A lateral radiograph of the lower vertebral column showed the
normal number and configuration of lumbar and sacral vertebrae but
there was a very prominent coccyx measuring 8.5 centimetres in length
and consisting of five well-developed vertebrae. Anteroposterior
radiographs of the pelvis showed a spina bifida of the first sacral
segment but an otherwise normal sacral configuration. The prominent
coccygeal vertebrae were again in evidence.
Partial excision of the coccyx was considered but not performed
because the parents believed that the symptoms were not severe
enough to warrant operation.
For creationists the human tail is the result of a mutation and not “the recurrence of a formerly expressed allele” - as Faith put it - because that would be evidence for a shared ancestor of humans and great apes. This has interesting consequences for the creationist viewpoint. For one this implies that benefical mutations should be quite common. Only in this century there are several documented cases where humans where born with a moveable tail containing connective tissue, nerves, blood vessels and muscles. In three cases tails containing vertebrae have been reported. On the other hand one would conclude that macroevolution understood as the development of new and complex biological structures has been observed in humans. -Bernd
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Do all creationists agree with the OP?
Thank you Dr. Adequate for your nice post! Hopefully I'm going to get some more more answers. So, would the real creationists please stand up and clarify the issue? -Bernd
| This message is a reply to: | | | Message 3 by Dr Adequate, posted 09-29-2006 12:54 PM | | Dr Adequate has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Message 8 of 61 (353956)
10-03-2006 4:24 PM
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Reply to: Message 1 by bernd
09-28-2006 9:24 PM
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A radiograph of a human tail
The following image taken from the article Human Tails
should illustrate that we are not talking about "a flacid rope of skin". Its a lateral radiograph which shows "the sacrum and three well developed coccygeal vertebrae" of a nine year old girl. (case three mentioned in the above linked article) So, how do creationists explain this? -Bernd
| This message is a reply to: | | | Message 1 by bernd, posted 09-28-2006 9:24 PM | | bernd has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, I’m sorry but I have some difficulties to understand your point. On page 32 of “A hundred years of evolution” we find the sentence: “If we interpret, as we clearly should, a single living filament as an ancestral stock, the position taken up by the grandfather is extraordinary close to that of the grandson in the ”Origin of Species’”. This usage of the term filament by Erasmus Darwin has obviously nothing to do with Faith’s way to describe a tail as a “flaccid rope of skin”. Please clarify what you tried to express. Besides that, please reread my opening post, where I indeed have asked how creationists “revolve” this “monster” in their minds, given that they probably can’t acknowledge “the recurrence of a formerly expressed allele” nor the origin of a complex structure by mutation. -Bernd
| This message is a reply to: | | | Message 9 by Brad McFall, posted 10-03-2006 4:39 PM | | Brad McFall has replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: regarding reference to the OP
Hello Brad, in your presentation of a creationist position you quoted Gish with:
Gish writes:
First of all, the caudal appendage does not contain even rudimentary vertebral structures
This position is falsified by the three cases with vertebrae presented in my opening post
Gish writes:
How can it be said that the presence of this "tail" brings us tangibly and inescapably to the reality of evolution if we cannot exclude the possibility that it is nothing more than a dermal appendage coincidently located in the caudal region? As a matter of fact, even a superficial reading of Ledley's article makes clear that this so-called tail was no tail at all but was nothing more than an anomalous growth coincidentally located in the caudal region.
Gish discusses an example of an pseudo-tail, not of a real human tail, therefore his argument is irrelevant. For a description of a real human tail please read Human tails and pseudotails Gish writes:
If this caudal appendage were due to a mutation, the mutant gene would be passed on to offspring and would eventually be reexpressed in some of those offspring. This has never been known to occur. The anomaly is thus not due to a mutation but to some disarrangement that occurred during embryological development.
There are documented cases that real human tails have been inherited (in one case over three generations of females) See: Standfast, A. L. (1992) "The human tail." New York State Journal of Medicine. 92: 116 You quote Gish with
Gish writes:
If malformations may possibly be due to the expression of genes inherited from distant ancestors but long suppressed
indicating that he may accept this as a possibilty. From the context it’s obvious, that he doesn’t consider this seriously. Besides that, admitting that a distant ancestor of homo sapiens had a tail is tantamount to admitting macroevolution. Finally you ask:
Brad writes:
And is there evidence that the "occupation" of a human tail IS the result of a complex mutational existence rather than a narrowed or broadend developmental constraint?
No, there is no evidence that the human tail is the result of “a complex mutational existence”. On the contrary it’s probably due to a mutation of a regulatory gene which controls the apoptosis of the tail in embryonic development. The problem for the creationist position is: Either admitting that homo sapiens has a working pathway to develop a tail which simply is repressed (and in the cases we are discussing unrepressed) - that would be evidence for an distant ancestor with a tail - or accepting the occurrence of mutations which construct de novo a tail with nerves, muscles, connective tissue and in some cases vertebrae. -Bernd Edited by bernd, : Typo Edited by bernd, : typo
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: The tale of a tail
Hello nemesis_yuggernaut, just to remember the topic of the opening post, we discuss how creationists explain true human tails. I would propose that we deal step for step with your post. In the first sentence you claim:
nemesis_juggernaut writes:
There is no musculature, nerve endings, or ligaments attached to these anamolies. All it is either a protuberant coccyx or distended skin, not a tail
Here are two article which contradict your claim: The abstract of
Human tails and pseudotails reads:
A case of a tail in a 2-week-old infant is reported, and findings from a review of 33 previously reported cases of true tails and pseudotails are summarized. The true, or persistent, vestigial tail of humans arises from the most distal remnant of the embryonic tail. It contains adipose and connective tissue, central bundles of striated muscle, blood vessels, and nerves and is covered by skin. Bone, cartilage, notochord, and spinal cord are lacking. The true tail arises by retention of structures found normally in fetal development. It may be as long as 13 cm, can move and contract, and occurs twice as often in males as in females. A true tail is easily removed surgically, without residual effects. It is rarely familial. Pseudotails are varied lesions having in common a lumbosacral protrusion and a superficial resemblance to persistent vestigial tails. The most frequent cause of a pseudotail in a series of ten cases obtained from the literature was an anomalous prolongation of the coccygeal vertebrae. Additional lesions included two lipomas, and one each of teratoma, chondromegaly , glioma, and a thin, elongated parasitic fetus.
In the abstract of The human tail: a benign stigma. Case report. we get some more infomation:
Thirty-three cases of true human tails have been reported in the modern English literature. A new case is described and its radiological and pathological features are presented. A review of the literature and analysis of the pathological characteristics of this interesting lumbosacral stigma indicate that the true human tail is a benign condition not associated with any underlying cord malformation.
So, can we agree that there are indeed documented cases of true human tails? -Bernd
| This message is a reply to: | | | Message 15 by Hyroglyphx, posted 10-05-2006 12:29 PM | | Hyroglyphx has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad,
Is there any evidence that human tail morphology has a functional purpose for the human lineage? THAT is what is at issue
No, that’s not the issue. When the human tail is not a atavistic structure, as creationists claim, how do they explain the development of this complex trait more than 33 times in this century? When on the other hand there is an existing pathway to develop a tail in humans which merely is repressed, how is this not evidence for a distant ancestor with a tail? Besides, I admit that creationist don’t have to assume that human tails are beneficial, there is most probably no evidence for that (My formulation in the opening post was badly worded, I should have written: mutations which give rise to new functions) On the other hand when mutations frequently create complex structure like the human tail doesn’t this provides more than enough traits selection can work on? So given that the rate of beneficial mutation is somehow dependant on the mutational input, wouldn’t we conclude that this rate will raise too? -Bernd Edited by bernd, : deleted the word "heritable" in second paragraph, see message 27 from Wonded King, Edited by bernd, : correction: replaced vestigal organ with atavistic structure in first paragraph
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Wounded King, thanks for the hint. I will correct this. -Bernd
| This message is a reply to: | | | Message 27 by Wounded King, posted 10-06-2006 5:12 AM | | Wounded King has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: regarding reference to apostacy.
Hello Brad, yes, I mean apoptosis. Thanks for pointing this out. -Bernd
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, With reference to my phrase:
When the human tail is not a vestigial organ, as creationists claim, how do they explain the development of this complex trait more than 33 times in this century?
you answered:
You seem to be starting from the thought that creationists have the idea FIRST that the tail is a vestigial organ for humans. I have tried to present a different path of possible creationist thought.
When I first started posting on the ICR web forum, before I was posting here, I noticed there was a tendency to speak about "vestigiality" a bit much. If ICR still has its discussion forum cached it might be possible to see how I dealt with this issue post by post, but I have not seen the Forum since then (about 1998).
If your issue REALLY has to start with a "vestigial organ" then the ANSWER has to do with the notion of "WILD TYPE." Is this the direction you are going (or wait till I post a second time to see an alternative).
Probably I have misled you by inexact wording. What I tried to express was that human tails are atavistic structures, in the sense that they are the “reappearance of a trait that had been present in a lineage in the past, but which had been absent in intervening generations”. (see Atavism - Wikipedia) . Creationists don’t accept that a tail is a trait which has been present in our lineage in the past, therefore they have two options: to claim that the tail is created de novo in each of the 33 cases which has been observed, or that there is a normaly repressed developmental pathway for tails in humans. Both options are difficult to harmonize with the creationist viewpoint, the first implies that mutation frequently generates complex features, the second is not only difficult to reconcile with the idea of an intelligent designer but would also be evidence for a shared ancestor of great apes and humans. But maybe there are options that I don’t see in the moment. I’m looking forward to your second post. -Bernd Edited by bernd, : typo Edited by bernd, : No reason given.
| This message is a reply to: | | | Message 29 by Brad McFall, posted 10-06-2006 4:15 PM | | Brad McFall has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, sorry for the late answer but I’m not familiar with the writings of Erasmus Darwin, so it took some time to compose this message. All the following quotes from E. Darwin are taken from “Zoonomia, Vol. I Or, the Laws of Organic Life” which can be downloaded from this link: Zoonomia; Or, the Laws of Organic Life, Vol. I by Erasmus Darwin - Free Ebook Lets start with your first question:
Brad writes:
I do not think it is difficult to "read" the Grandfather's use of the word "filament" as a precursor idea to Charles' use of "common descent"? Yes???
E. Darwin has formulated common descent as hypothesis, so far I agree. But I don’t think that this idea is somehow included in the term filament as you seem to claim in your sentence:
Brad writes:
Now look CLOSELY at how Erasmus thought out the transformation and notice how the Elder Darwin leads his "mind" to the notion of a "filament" as a conclusion and unity of the thought of biological form-making and translation in space
Let’s examine two quotes:
E.Darwin writes:
I shall only add here, that it is probable, that this sympathy does not depend on any communication of nervous filaments, but on habit; owing to the various branches of this system having frequently been stimulated into action at the same time
E.Darwin writes:
The whole animal system may be considered as consisting of the extremities of the nerves, or of having been produced from them; if we except perhaps the medullary part of the brain residing in the head and spine, and in the trunks of the nerves. These extremities of the nerves are either of those of locomotion, which are termed muscular fibres; or of those of sensation, which constitute the immediate organs of sense, and which have also their peculiar motions. Now as the fibres, which constitute the bones and membranes, possessed originally sensation and motion; and are liable again to possess them, when they become inflamed; it follows, that those were, when first formed, appendages to the nerves of sensation or locomotion, or were formed from them. And that hence all these solid parts of the body, as they have originally consisted of extremities of nerves, require an apposition of nutritive particles of a similar kind, contrary to the opinion of Buffon and Needham above recited. Lastly, as all these filaments have possessed, or do possess, the power of contraction, and of consequent inertion or elongation; it seems probable, that the nutritive particles are applied during their times of elongation; when their original constituent particles are removed to a greater distance from each other. For each muscular or sensual fibre may be considered as a row or string of beads; which approach, when in contraction, and recede during its rest or elongation; and our daily experience shews us, that great action emaciates the system, and that it is repaired during rest.
In this two examples Darwin uses the tems fibre and filament as defined in anatomy - obviously without connotation of common descent. More interesting is his use of the term “living filament”. For example here:
E.Darwin writes:
1. I conceive the primordium, or rudiment of the embryon, as secreted from the blood of the parent, to consist of a simple living filament as a muscular fibre; which I suppose to be an extremity of a nerve of loco-motion, as a fibre of the retina is an extremity of a nerve of sensation; as for instance one of the fibrils, which compose the mouth of an absorbent vessel; I suppose this living filament, of whatever form it may be, whether sphere, cube, or cylinder, to be endued with the capability of being excited into action by certain kinds of stimulus. By the stimulus of the surrounding fluid, in which it is received from the male, it may bend into a ring; and thus form the beginning of a tube. Such moving filaments, and such rings, are described by those, who have attended to microscopic animalcula. This living ring may now embrace or absorb a nutritive particle of the fluid, in which it swims; and by drawing it into its pores, or joining it by compression to its extremities, may increase its own length or crassitude; and by degrees the living ring may become a living tube.
The “moving filaments” which Darwin describes are probably sperms, he thinks that the mother only provides the nutrients for the embryo. He contends that his concept can be generalised:
E.Darwin writes:
All animals therefore, I contend, have a similar cause of their organization, originating from a single living filament, endued indeed with different kinds of irritabilities and sensibilities, or of animal appetencies; which exist in every gland, and in every moving organ of the body, and are as essential to living organization as chemical affinities are to certain combinations of inanimate matter.
He argues then that a process which transforms a simple filament into an organism, may also form the diversity of warm blooded animals, given that they share a similar structure (that's a simplification but it should do within the context of this thread)
E.Darwin writes:
Fourthly, when we revolve in our minds the great similarity of structure, which obtains in all the warm-blooded animals, as well quadrupeds, birds, and amphibious animals, as in mankind; from the mouse and bat to the elephant and whale; one is led to conclude, that they have alike been produced from a similar living filament
Please note that "mankind" is included in the warm-blooded animals. A similar argument is made for cold-blooded animals:
E.Darwin writes:
The cold-blooded animals, as the fish-tribes, which are furnished with but one ventricle of the heart, and with gills instead of lungs, and with fins instead of feet or wings, bear a great similarity to each other; but they differ, nevertheless, so much in their general structure from the warm-blooded animals, that it may not seem probable at first view, that the same living filament could have given origin to this kingdom of animals, as to the former. Yet are there some creatures, which unite or partake of both these orders of animation, as the whales and seals; and more particularly the frog, who changes from an aquatic animal furnished with gills to an aerial one furnished with lungs.
After discussing plants he poses the question:
E.Darwin writes:
Shall we then say that the vegetable living filament was originally different from that of each tribe of animals above described? And that the productive living filament of each of those tribes was different originally from the other? Or, as the earth and ocean were probably peopled with vegetable productions long before the existence of animals; and many families of these animals long before other families of them, shall we conjecture that one and the same kind of living filaments is and has been the cause of all organic life
The following paragraphs suggest that he believes that all organic life comes from one living filament. He goes even further:
E.Darwin writes:
The late Mr. David Hume, in his posthumous works, places the powers of generation much above those of our boasted reason; and adds, that reason can only make a machine, as a clock or a ship, but the power of generation makes the maker of the machine; and probably from having observed, that the greatest part of the earth has been formed out of organic recrements; as the immense beds of limestone, chalk, marble, from the shells of fish; and the extensive provinces of clay, sandstone, ironstone, coals, from decomposed vegetables; all which have been first produced by generation, or by the secretions of organic life; he concludes that the world itself might have been generated, rather than created; that is, it might have been gradually produced from very small beginnings, increasing by the activity of its inherent principles, rather than by a sudden evolution of the whole by the Almighty fire.”What a magnificent idea of the infinite power of THE GREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS! ENS ENTIUM!
An additional remark. The word “PLAN” doesn’t occur in the whole text. Considering what I have listed above, I don’t follow your observation that Darwin speaks of a “PLAN” only with respect to warm-blooded creatures nor that snakes or humans are somehow treated specially. I’m not quite sure what you tried to express with “E. Darwins restricted reference to taxonomy”, but from the text it's clear that he speculates about universal common descent. Finally I would ask you to rephrase your last two sentences, I do not understand, what you are trying to say. (What does “beling” mean? Or did you intend to write "belong"?) I hope this will clarify the basic question whether and in which way your message deals with the topic at hand: Are human tails an example of macroevolution. -Bernd Edited by bernd, : No reason given. Edited by bernd, : No reason given. Edited by bernd, : spelling,syntax,clarification
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, you asked:
Also you might be able to confirm if I am correct that it was GGaylordSimpson who first worked out the notion of throw-back or atavism BUT IN MAMMALS only?? That is what I recall.
Simpson didn’t introduce this term. It was already in use when Charles Darwin wrote The variation of animals and plants under domestication , as you can see by the first sentence of chapter 13:
THE great principle of inheritance to be discussed in this chapter has been recognised by agriculturists and authors of various nations, as shown by the scientific term Atavism, derived from atavus, an ancestor; by the English terms of Reversion, or Throwing-back; by the French Pas-en-Arrire; and by the German Rckschlag, or Rckschritt.
With regard to the notion of atavism have a look at chapter 5 of The origin of species. Darwin describes an example of a reversion (or atavism) in horses and pigeons. His concluding remarks are:
What now are we to say to these several facts? We see several very distinct species of the horse-genus becoming, by simple variation, striped on the legs like a zebra, or striped on the shoulders like an ass. In the horse we see this tendency strong whenever a dun tint appears-a tint which approaches to that of the general colouring of the other species of the genus. The appearance of the stripes is not accompanied by any change of form or by any other new character. We see this tendency to become striped most strongly displayed in hybrids from between several of the most distinct species. Now observe the case of the several breeds of pigeons: they are descended from a pigeon (including two or three sub-species or geographical races) of a bluish colour, with certain bars and other marks; and when any breed assumes by simple variation a bluish tint, these bars and other marks invariably reappear; but without any other change of form or character. When the oldest and truest breeds of various colours are crossed, we see a strong tendency for the blue tint and bars and marks to reappear in the mongrels. I have stated that the most probable hypothesis to account for the reappearance of very ancient characters, is-that there is a tendency in the young of each successive generation to produce the long-lost character, and that this tendency, from unknown causes, sometimes prevails. And we have just seen that in several species of the horse-genus the stripes are either plainer or appear more commonly in the young than in the old. Call the breeds of pigeons, some of which have bred true for centuries, species; and how exactly parallel is the case with that of the species of the horse-genus! For myself, I venture confidently to look back thousands on thousands of generations, and I see an animal striped like a zebra, but perhaps otherwise very differently constructed, the common parent of our domestic horse, whether or not it be descended from one or more wild stocks, of the ass, the hemionus, quagga, and zebra.
(original without bold face) -Bernd
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: work in process
Hello Brad, thank you for your interesting excerpts. While you are preparing your second post - please take your time - maybe you find the following links helpful. About the development of the vertebrate tail:
The vertebrate tail is an extension of the main body axis caudal to the anus. The developmental origin of this structure has been a source of debate amongst embryologists for the past century. Some view tail development as a continuation of the morphogenetic processes that shape the head and trunk (i.e. gastrulation). The alternative view, secondary development, holds that the tail forms in a manner similar to limb development, i.e. by secondary induction. Previous developmental studies have provided support for both views. Here I revisit these studies, describing caudal morphogenesis in select vertebrates, the associated genes and developmental defects, and, as a relevant aside, consider the developmental and evolutionary relationships of primary and secondary neurulation. I conclude that caudal development enlists both gastrulation and secondary induction, and that the application of recent high-resolution cell labelling technology may clarify how these discordant programmes interact in building the vertebrate tail.
from
Concordia discors: duality in the origin of the vertebrate tail About apoptosis of the embryonic human tail:
During normal human development a number of transient structures form and subsequently regress completely. One of the most prominent structures that regress during development is the human tail. We report here a histological and ultrastructural study of cell death in the cranial and caudal (tail) parts of the neural tube in 4 to 6-week-old human embryos. Initially, the human tail is composed of tail bud mesenchyme which differentiates into caudal somites, secondary neural tube, notochord and tail gut. Later on, these structures gradually regress by cell death. During the investigated period, we observed two morphologically distinct types of dying cells. The well-described apoptotic type of cell death was observed only in the cranial neural tube that forms during primary neurulation. The other type of cell death characterized by necrotic morphology was observed in the tail mesenchyme and in the caudal neural tube that forms during secondary neurulation. This morphological diversity suggests that besides differences in origin and fate there are different mechanisms of developmental cell death between two parts of the human neural tube. We can speculate that the apoptotic type of cell death is associated with the precise control of cell numbers and that the other morphologically distinct type of cell death is responsible for the massive removal of transitory structures
from Morphological diversity of dying cells during regression of the human tail About canalisation:
Progress on canalization Waddington's canalization revisited: Developmental stability and evolution Have a nice day! -Bernd
| This message is a reply to: | | | Message 35 by Brad McFall, posted 10-08-2006 2:55 PM | | Brad McFall has not replied |
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, You wrote:
If you think this use of Gould's figure is a little premature, a simple indication such, will have me work out a more extensive critical position
No, at the moment I have no problems with that figure. Let’s go on with our discussion. I am looking forward to your second post. Besides, thanks again for your quotes from Gould: The Structure of Evolutionary Theory. -Bernd
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bernd
Member (Idle past 4011 days) Posts: 95 From: Munich,Germany Joined: 07-10-2005
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Re: A radiograph of a human tail
Hello Brad, You mentioned a potential falsification of your approach:
This idea would be wrong if the regulatory genes for tail expression was found conserved as in hox genes for general segmentation. It is also possible that some aspect of hoxology may disrupt my structural prescription for which I was trying to take more time to figure out. I wanted to get the general stages in the argument out however even if I am completely off base here. So that others can do some of of the surfing as well
I take this to mean that if we find the same regulatory genes that control the tail phenotype lets say in mice also in humans, we would have to assume that “evolutionary history” is a good explanation of the rare occurrence of this phenotype in men. So let’s start with a hox gene. Hoxb-13 has been found in both human and mice (see:
Hoxb-13: a new Hox gene in a distant region of the HOXB cluster maintains)
Colinearity The function for tail development in mice has been detailed here:
To address the expression and function of Hoxb13, the 5_ most Hox gene in the HoxB cluster, we have generated mice with loss-of-function and _-galactosidase reporter insertion alleles of this gene. Mice homozygous for Hoxb13 loss-of-function mutations show overgrowth in all major structures derived from the tail bud, including the developing secondary neural tube (SNT), the caudal spinal ganglia, and the caudal vertebrae. Using the _-galactosidase reporter allele of Hoxb13, also a loss-of-function allele, we found that the expression patterns of Hoxb13 in the developing spinal cord and caudal mesoderm are closely associated with overgrowth phenotypes in the tails of homozygous mutant animals. These phenotypes can be explained by the observed increased cell proliferation and decreased levels of apoptosis within the tail of homozygous mutant mice. This analysis of Hoxb13 function suggests that this 5_ Hox gene may act as an inhibitor of neuronal cell proliferation, an activator of apoptotic pathways in the SNT, and as a general repressor of growth in the caudal vertebrae.
from
Hoxb13 mutations cause overgrowth of caudal spinal cord
and tail vertebrae Considering the role of Hox genes in pattering the anterior posterior axis in all mamals, I think it’s probable that the gene has had a similar functions in the ancestor of humans and great apes. Another confirmation of a shared genetic base for tail development can be found when looking at Wnt3-a, a regulatory gene found in all vertebrates. In mice it plays an important role in tail development. When its expression is downregulated, for example by treating diabetic mice with retinoic acid, the the probability of a caudal regression is significantly increased. Similar defects under equal circumstances - diabetes in interaction with RA - are observed in humans:
Maternal diabetes increases the risk of congenital malformations in the offspring of affected pregnancies. This increase arises from the teratogenic effect of the maternal diabetic milieu on the developing embryo, although the mechanism of this action is poorly understood. In the present study, we examined whether the vitamin A metabolite retinoic acid (RA), a common drug with well-known teratogenic properties, may interact with maternal diabetes to alter the incidence of congenital malformations in mice. Our results show that when treated with RA, embryos of diabetic mice are significantly more prone than embryos of nondiabetic mice to develop caudal regression, a defect that is highly associated with diabetic pregnancy in humans. By studying the vestigial tail (Wnt-3a(vt)) mutant, we provide evidence that Wnt-3a, a gene that controls the development of the caudal region, is directly involved in the pathogenic pathway of RA-induced caudal regression. We further show that the molecular basis of the increased susceptibility of embryos of diabetic mice to RA involves enhanced downregulation of Wnt-3a expression. This positive interaction between RA and maternal diabetes may have implications for humans in suggesting increased susceptibility to environmental teratogens during diabetic pregnancy
from Maternal diabetes increases the risk of caudal regression caused by retinoic acid Besides, in this article you’ll find an overview about segmentation in vertebrates and the role of Wnt3-a in this process. Have a look at figure 2 in the chapter “Gradient and clock are joined through Wnt3a” Finally, a request for clarification. Could you please explain in greater detail what exactly is a "grave of a cell death"? The other point would be to explain why you think that there is no lower bound to a valley of an adaptive landscape. Quotes would be appreciated. -Bernd
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