Tuesday, March 07, 2006

Scientists Find Chickens Retain Ancient Ability to Grow Teeth, etc

Scientists Find Chickens Retain Ancient Ability to Grow Teeth, ABC News, Ammu Kannampilly ... Feb. 27, 2006 .... Scientists from the universities of Wisconsin-Madison and Manchester, U.K., have reason to rejoice after a successful experiment, which caused hens to grow conical, saber-shaped teeth. This curious experiment was carried out by researchers studying the ancestry of birds and their evolution from flying, nonavian reptiles to the feathered creatures we now know. "I was looking for feathers on the head of a mutant chicken embryo, and I noticed these formations along the edge of the beak that looked like alligator teeth," said lead researcher Matthew Harris, who specializes in the study of evolution and development. The mutant chicken embryos that Harris studied possess a recessive and lethal trait called talpid2. As embryos, they can survive in eggs for as long as 18 days, but they never make it to the hatching stage (chickens normally hatch after 21 days). During their incubation, these mutant embryos begin to grow nascent teeth, like those found in ancient bird fossils. When Harris and his colleagues "turned on" the talpid2 gene in the oral cavity of a normal chicken embryo, they found that the mutation caused the tissues in the embryo's jaw to initiate the formation of teeth, very much like those belonging to the bird's ancestors. What makes this experiment unique is the fact that, unlike earlier experiments, it involved no grafting or tissue transplants from a mutant chicken. John Fallon of the University of Wisconsin, who oversaw the project, said "These results provide clear evidence that these chickens possess the memory of the past; they have retained the ability to make teeth, under certain conditions. [See also EurekAlert! There is nothing really new in this. Gould in 1983 (~23 years ago), in an aptly named article, "Hen's Teeth and Horse's Toes" (originally in Natural History and later reprinted in a book of essays of the same name) commented on a 1980 paper (Kollar E.J. & Fisher C., "Tooth induction in chick epithelium: expression of quiescent genes for enamel synthesis," Science, Vol. 207, February 29, 1980, pp.993-5) which reported on an experiment in which chicken and mouse embryonic tissues were combined and then transplanted into the eye tissue of a living mouse embryo, which then grew teeth:

"My latent interest in atavism was recently kindled by a report of something that has no right to exist if one of our most venerable similes expresses literal truthhen's teeth. On February 29, 1980 ... E.J Kollar and C. Fisher reported an ingenious technique for coaxing chickens to reveal some surprising genetic flexibility retained from a distant past. They took epithelial (outer) tissue from the first and second gill arches of a fiveday-old chick embryo and combined it with mesenchyme (inner embryonic tissue) of sixteen-to eighteen-day-old mouse embryos taken from the region where first molar teeth form. ... Kollar and Fisher took the combined embryonic tissue of mouse and chicken and grew it in ... the anterior chambers of the eyes of adult nude mice ... In ordinary teeth, made by a single animal, the outer enamel layer forms from epithelial tissue and the underlying dentin and bone from mesenchyme. But mesenchyme cannot form dentin (although it can produce bone) unless it can interact directly with epithelium destined to form enamel. (In embryological jargon, epithelium is a necessary inducer, although only mesenchyme can form dentin.) When Kollar and Fisher grafted mouse mesenchyme alone into the eyes of their experimental animals, no dentin developed, but only spongy bone-the normal product of mesenchyme when deprived of contact with enamel epithelium as an inducer. But among fifty-five combined grafts of mouse mesenchyme and chick epithelium, ten produced dentin. Thus, chick epithelium is still capable of inducing mesenchyme (from another species in another vertebrate class yet!) to form dentin. Archaeopteryx, the first bird, still possessed teeth, as did several fossils from the early history of birds. But no fossil bird has produced teeth during the past sixty million years, while the toothlessness of all modern birds ranks with wings and feathers as defining characters of the class. Nonetheless, although the system has not been used on its home ground for perhaps a hundred million generations, chick epithelium can still induce the formation of dentin when combined with appropriate mesenchyme (chick mesenchyme itself has probably lost the ability to form dentin, hence the toothlessness of hens and the necessity for using mice). Kollar and Fisher then found something even more interesting. In four of their grafts, complete teeth had developed! Chick epithelium had not only induced mouse mesenchyme to form dentin; it had also been able to generate enamel matrix proteins. (Dentin must be induced by epithelium, but this epithelium cannot differentiate into enamel unless it, in turn, can interact with the very dentin it has induced. Since chick mesenchyme cannot form dentin, chick epithelium never gets the chance to show its persistent stuff in nature.) ... Kollar and Fisher write of their best tooth: `The entire tooth structure was well formed, with root development in proper relation to the crown, but the latter did not have the typical first-molar morphology, since it lacked the cusp pattern usually present in intraocular grafts of first-molar rudiments.' In other words, the tooth looks normal, but it does not have the form of a mouse's molar. The odd form may, of course, simply result from the peculiar interaction of two systems not meant to be joined in nature. But is it possible that we are seeing, in part, the actual form of a latent bird's tooth-the potential structure that chick epithelium has encoded for sixty million years but has not expressed in the absence of dentin to induce it?" (Gould S.J., "Hen's Teeth and Horse's Toes," in "Hen's Teeth and Horse's Toes: Further Reflections in Natural History," [1983], Penguin: London, 1986, reprint, pp.183-184)

What I am describing is evolution." Fallon's specialty is developmental biology, particularly vertebrate limb development and pattern formation. The scientists discounted the possibility of this experiment having any direct medical application (to stimulate tooth regrowth in humans, for example). But they insisted on its importance to the human understanding of evolution, with Harris arguing that "the results of this experiment hit home, highlighting the potential in our genes to re-form what once existed. "There are so many examples of such atavistic traits -- snakes with vestigial limbs, horses with three toes, even human beings who have hair growing all over their body and face," he said. "As far as I am concerned, this experiment vindicates the theory of evolution as it exposes the evolutionary history of birds. [Since the only possibility allowed is "evolution" then by definition what Fallon is "describing is evolution." But that is to confuse common ancestry with evolution when quite clearly they are not necessarily the same thing.

And as Gould pointed out in his article, this was a problem for Darwinian evolution, which holds that "major transitions are a summation of the small changes that adapt populations ever more finely to their local environments" when "major transitions" may be the result of "Small changes in the timing of ... controllers" and "master switches" which "translate into major and discontinuous alterations of external form":

"I would suggest an opposite view-that atavisms teach an important lesson about potential results of small genetic changes, and that they suggest an unconventional approach to the problem of major transitions in evolution. In the traditional view, major transitions are a summation of the small changes that adapt populations ever more finely to their local environments. Several evolutionists, myself included, have become dissatisfied with this vision of smooth extrapolation. Must one group always evolve from another through all insensibly graded series of intermediate forms? Must evolution proceed gene by gene, each tiny change producing a correspondingly small alteration of external appearance? The fossil record rarely records smooth transitions, and it is often difficult even to imagine a function for all hypothetical intermediates between ancestors and their highly modified descendants. One promising solution to this dilemma recognizes that certain kinds of small genetic changes may have major, discontinuous effects upon morphology. We can make no one-to-one translation between extent of genetic change and degree of alteration in external form. Genes are not attached to independent bits of the body, each responsible for building one small item. Genetic systems are arranged hierarchically; controllers and master switches often activate large blocks of genes. Small changes in the timing of action for these controllers often translate into major and discontinuous alterations of external form." (Gould, Ibid, pp.180-181)

But then the problem for naturalistic `blind watchmaker' evolution is, what (or who) built these "Genetic systems ... arranged hierarchically" with "controllers and master switches" that can "activate large blocks of genes" such that "Small changes in the timing of action for these controllers often translate into major and discontinuous alterations of external form"?

Supporters of intelligent design will have to scramble to explain this one!" ... [First, Fallon pays " intelligent design" the compliment of conceding that it is a scientific rival that can be falsified by empirical facts! And I agree that those "supporters of intelligent design" who obligingly play their part in the script written for them by Darwin, in equating both creation (and intelligent design) with the straw man that Darwin erected abd attacked in his Origin of Species, namely "the dogma of separate creations." (Darwin C.R., "The Descent of Man," John Murray: London, Second Edition, 1874, p.92), will have difficulty in plausibly explaining this. But in fact Fallon shows his ignorance in confusing "intelligent design" with separate creations. One of ID's leaders, Bill Dembski, has stated that, "intelligent design is compatible with ... the most far-ranging evolution (e.g., God seamlessly melding all organisms together into one great tree of life)" (Dembski W.A., "Intelligent Design," InterVarsity Press: Downers Grove IL, 1999, pp.109-110). And another ID leader Mike Behe, accepts "the idea of common descent (that all organisms share a common ancestor)" (Behe M.J., "Darwin's Black Box," Free Press: New York NY, 1996, pp.5-6), as I do. And what Harris demonstrated (albeit crudely) was not analogous to unintelligent `blind watchmaker' "evolution" but how intervention in normal natural processes by an intelligent agent can produce major changes in a single generation, which is analogous to intelligent design!]

Geologist Alvarez Wins Top Research Prize, ABC News/AP, Scott Sonner ... RENO, Nev. Mar 5, 2006 (AP) - A geologist who proposed the theory that a comet or asteroid smashed into the Earth and killed off the dinosaurs is the winner of a top research award. Walter Alvarez, a geologist at the University of California-Berkeley, is the 19th recipient of the nonprofit Desert Research Institute's silver medallion and its $20,000 prize. ... Alvarez's nearly two decade-long investigation produced an uncommon scientific drama of personal tenacity and ingenuity, said Stephen G. Wells, president of the institute. "Until the impact theory was finally proven, Dr. Alvarez and his colleagues were regarded as heretics by the `old guard' in the field of geology," Wells said. The theory dates to the 1970s in Italy, where Alvarez and his colleagues found high levels of the element iridium, which is extremely rare on Earth, but common in comets and asteroids. They theorized it must have come from a giant asteroid that sent smoke, dust and iridium into the sky, blocking the sun, lowering the earth's temperature and eventually killing off plants and many species. Alvarez's theory, first published in the journal Science in 1980, had few supporters until scientists found evidence of a huge impact crater on Mexico's Yucatan Peninsula in 1989. Later studies found evidence of debris from Mexico distributed by tsunamis that went as far as what is now Arkansas. ... [This is an example of how almost an entire scientific field can be wrong on a major issue, even when the "heretics" (Walter Alvarez and his father Nobel laureate Luis Alvarez) are scientific materialists. It is therefore not hard for me to imagine how an entire field, evolution, can be wrong on a major issue, namely in adopting "the standard scientific theory that `human beings have developed over millions of years from less advanced forms of life, but God had no part in this process.'" (Shermer M.B., "The Gradual Illumination of the Mind," Scientific American, February 2002. My emphasis). The point is that "human beings" may well "have developed over millions of years from less advanced forms of life" (in fact I accept that they have) but if God did have a part in this process (e.g. supernaturally intervened at strategic points to add new information), a science dominated (90-95%) by atheists/agnostics would never be able to even consider it, let alone accept it!]

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"

2 comments:

Jorolat said...

I think one of the points that Harris and Fallon were making was that no 'alien' tissue had been introduced. From the summary of "The Development of Archosaurian First-Generation Teeth in a Chicken Mutant":

Although recombination studies have shown that the avian epidermis can respond to tooth-inductive cues from mouse or lizard oral mesenchyme and participate in tooth formation 1; 2, attempts to initiate tooth development de novo in birds have failed. Here, we describe the formation of teeth in the talpid2 chicken mutant, including the developmental processes and early molecular changes associated with the formation of teeth.

Stephen E. Jones said...

John

John Latter said...

>I think one of the points that Harris and Fallon were making was that no 'alien' tissue had been introduced.

Thanks for your comment and agreed. By working only with a chicken Harris & Fallon had removed any doubt there was that it was the mouse genes and tissue only that grew the teeth in Kollar and Fisher's experiment.

But most (including me) had long accepted that Kollar and Fisher had provided further evidence that birds had retained the genetic potential to develop teeth and therefore provided more evidence for common ancestry. Although Archaeopteryx (which I saw in London in 1997) already had from the 19th century shown that.

The main point of my post (although maybe I did not make it as clear as I could have) was the fallacious assumption that common ancestry = evolution. It doesn't, since a Designer/God could supernaturally intervene at links in ancestor-descendent chains, and Darwin was well aware of that, since some creationists (like the Duke of Argyll) proposed just that.

And also I wanted to again make the point that "Supporters of intelligent design" do *not* "have to scramble to explain this one" because ID has no reason to oppose common ancestry (since ID is not Biblical literalism with its doctrine of separate creations) and in fact leading IDists like Behe (and lesser lights like myself) accept common ancestry).

Indeed, as I indicated, it is the *Darwinists* who "have to scramble to explain this one!"

Stephen E. Jones