Hen's Teeth

[ST88]

Mutant Chicken Grows Alligatorlike Teeth

Working late in the developmental biology lab one night, Matthew Harris of the University of Wisconsin noticed that the beak of a mutant chicken embryo he was examining had fallen off. Upon closer examination of the snubbed beak, he found tiny bumps and protuberances along its edge that looked like teeth--alligator teeth to be specific. The accidental discovery revealed that chickens retain the ability to grow teeth, even though birds lost this feature long ago.
-- Scientific American

I am not one to jump to conclusions easily, so I would like to ask the question. If a bird embryo has the ability to grow teeth -- something which birds do not need nor to our knowledge have they ever had -- where did that ability come from? More specifically, where could it possibly have come from except via a vestigial genetic function? Recall that mutations like this can't come from nowhere. The coding for "teeth" in genes does not happen overnight. This is something that Creationists have pointed out -- rightly -- for some time. They have been screaming for an example of morphological changes exhibited via a genetic mutation. Well, here you go.

There are other less spectacular examples of this (snakes with legs, horses with multiple hooves on one leg), but to my knowledge, this is the first time that an organism has exhibited traits from a previous class of animals -- reptile features in an avian organism. So, does this put an end to the debate, &/or does it begin new ones?

[Cathar1950]

I was reading about this the other day when the site went down and then I couldn't remember what thread we were talking about the subject.

You do bring an interesting point. I remember reading some place in some mag. Sci. Amer. I think where the were finding the dna codes for eyes in worms or something like that. It was a matter of turning codes on and off for life forms development with genes.
But I was thinking maybe as life developed at some time other paths taken carry all they are going to have excluding other mutations.
It seems what it does say is that life forms are related which would not discredit evolution in any way. It might be a clue to the mechanism involved in evolution of life with natural selection(continuing) being the final abritrator of success.
I thought it was very interesting.

[Jose]

So, does this put an end to the debate, &/or does it begin new ones?

In the end, it will have no effect on the debate. It's actually been known for years and years that chickens have the genes for dentine (regrettably, I can't find the paper--somewhere in the 80's). But, the fact that chickens have tooth genes, but don't use them, hasn't been particularly noteworthy in the debate. Then, it was shown that one could induce tooth formation in chick embryos by transplanting the relevant inducing tissue from mouse embryos (refs 1,2), thereby demonstrating that the whole tooth-development pathway is there...and still, there was little notice.

The most recent paper (ref 3) suggests that the "problem" with birds is that the inducing cells and the responding cells don't get close enough together to "talk to" each other. This is quite cute, actually--a simple mutation that affects the contact of two cell types can have a seemingly-huge phenotypic effect of knocking out an entire developmental pathway.

The earlier findings weren't picked up by Scientific American...that may make a difference. We can keep our fingers crossed...but then, it's always possible to say "that's how god created chickens," useless genes and all.

- - - - - - -

Kollar and Mina (1991). Role of the early epithelium in the patterning of the teeth and Meckel’s cartilage. J. Craniofac. Genet. Dev. Biol. 11, 223–228.

Mitsiadis et al., (2003) Development of teeth in chick embryos after mouse neural crest transplantations. Proc Natl Acad Sci USA 100: 6541-45.

Harris,et al. (2006) The Development of Archosaurian First-Generation Teeth in a Chicken Mutant. Curr Biol. 2006 Feb 21;16(4):371-7.

[ST88]

It's actually been known for years and years that chickens have the genes for dentine (regrettably, I can't find the paper--somewhere in the 80's). But, the fact that chickens have tooth genes, but don't use them, hasn't been particularly noteworthy in the debate. Then, it was shown that one could induce tooth formation in chick embryos by transplanting the relevant inducing tissue from mouse embryos (refs 1,2), thereby demonstrating that the whole tooth-development pathway is there...and still, there was little notice.

Isn't this because the Creationist laity doesn't pay attention to scientific journals? Creationism persists because people have complaints against evolution that seem like science, but are actually dealt with in the world of science. Unfortunately, no one sees that the complaints are dealt with. And they come up again and again, whereas scientists think (rightly) that the questions have already been answered and so pay no attention to them. Then it comes the time when the scientific background of a "problem" is all but forgotten by the laity, and these people get into government positions. In this way, the Creationist argument is about PR -- there has little in the way of scientific arguments that make any sense.

The beauty of this story is that it is a spectacular example of how mutations work -- not little by little -- not "half an eye" mutating to an eye; but a vestige of an evolutionary past that can't be explained by Creationism. And if it stays in the public consciousness, the questions will be PR against Creationism. It's not that this sort of thing has been known for a long time, it's that it's a graphic example of an answer to a major Creationist complaint.

It's also an example of something that was not "induced" by scientists, instead it was a natural mutation (i.e., God allowed it to happen).

The earlier findings weren't picked up by Scientific American...that may make a difference. We can keep our fingers crossed...but then, it's always possible to say "that's how god created chickens," useless genes and all.

Even if true, YEC goes out the window. One of YEC's predicates is that genetic mutations do not produce new morphological characters. These are PR hits in addition to scientific ones, and that is how minds are changed.

[Jose]

You're right, ST88, it is because the laity doesn't read scientific journals. It's compounded by the fact that science reporters generally don't either, and by the fact that we science geeks tend not to make a lot of noise (ie press conferences) when we discover cool things. It seems sort of tacky to do so.

But this one, of actual chicken teeth, now that captures the imagination. Regrettably, the talpid(2) mutation also causes polydactyly, with the extra digits in the wing all being morphologically identical, and it causes some other abnormalities that result in lethality. So, we can't (yet) grow adult chickens that can really bite us. No doubt, they'll try to weasel out of it by saying that "it doesn't count" because so many things go wrong.

Still, it leaves the puzzling question of why an "intelligent" designer would put perfectly good tooth genes into chickens, if chickens don't bother to use them to make teeth. What are the genes for? A vestige of evolutionary history makes perfectly good sense, but sloppy design does not.

[rigadoon]

But this one, of actual chicken teeth, now that captures the imagination. Regrettably, the talpid(2) mutation also causes polydactyly, with the extra digits in the wing all being morphologically identical, and it causes some other abnormalities that result in lethality. So, we can't (yet) grow adult chickens that can really bite us. No doubt, they'll try to weasel out of it by saying that "it doesn't count" because so many things go wrong.

Capturing the imagination -- a few bumps on a chicken and the imaginations of some people go wild. So all you need is to pick and choose among the evidence and let your imagination do the rest.

Still, it leaves the puzzling question of why an "intelligent" designer would put perfectly good tooth genes into chickens, if chickens don't bother to use them to make teeth. What are the genes for? A vestige of evolutionary history makes perfectly good sense, but sloppy design does not.

If it's a vestige of something, show us the something. It could just as easily be a vestige of a former perfection. The word "vestige" doesn't have any magical powers of explanation.

[micatala]

Capturing the imagination -- a few bumps on a chicken and the imaginations of some people go wild. So all you need is to pick and choose among the evidence and let your imagination do the rest.

Why so disparaging? This is an interesting bit of evidence. I don't see that Jose is 'letting his imagination go wild.' It is also unfair to conclude that Jose or anyone else is only selectively using evidence simply because it is this particular bit of evidence that we are currently discussing. What relevant evidence can you point to that is being left out?

If it's a vestige of something, show us the something. It could just as easily be a vestige of a former perfection. The word "vestige" doesn't have any magical powers of explanation.

I'm not sure what you mean. Are you disagreeing that the teeth are evidence that ancestors of this hen possessed teeth? What difference does it make if we cannot say exactly what this ancestor or even its teeth looked like? The genes that code for teeth are there. If they did not get there because a previous ancestor had these genes, how did they get there?

[Grumpy]

rigadoon



Notice the tiny little teethys???

Grumpy 8)

[rigadoon]

Capturing the imagination -- a few bumps on a chicken and the imaginations of some people go wild. So all you need is to pick and choose among the evidence and let your imagination do the rest.

Why so disparaging? This is an interesting bit of evidence. I don't see that Jose is 'letting his imagination go wild.' It is also unfair to conclude that Jose or anyone else is only selectively using evidence simply because it is this particular bit of evidence that we are currently discussing. What relevant evidence can you point to that is being left out?

I didn't mean leaving out evidence but arranging evidence with a particular imagination spinning stories and filling in gaps (an imagination of the gaps). If science is to be objective, then a particular imagination should not be pre-supposed. Ignore your imagination -- then what do you get?

If it's a vestige of something, show us the something. It could just as easily be a vestige of a former perfection. The word "vestige" doesn't have any magical powers of explanation.

I'm not sure what you mean. Are you disagreeing that the teeth are evidence that ancestors of this hen possessed teeth? What difference does it make if we cannot say exactly what this ancestor or even its teeth looked like? The genes that code for teeth are there. If they did not get there because a previous ancestor had these genes, how did they get there?

Yes, I'm disagreeing that a conclusion about events in the distant past can be scientifically made on such a flimsy basis.

[micatala]

Well, I don't know that I would agree that the evidence is 'flimsy', but ignoring that, what is your explanation of how the teeth, or the genes for teeth got into this hen?