Ever changing science.

Rize · Jan 27, 2003

Originally posted by lucaspa
Let's not try tails in humans, but tails in ascidians. 
"Tracing a Backbone's Evolution Through a Tunicate's Lost Tail"  Science vol. 274, pp 1082-1083, Nov. 15, 1996'  Primary article is "Requirement of the Manx Gene for Expression of Chordat Freatures in a Tailless Ascidian Larvae"  pp 1205-1208.

Adult tunicates are sedentary sea-dwellers with no sign of a backbone, and they live like mussels, attached to a shell or rock and filtering food through chimney-like siphons.  However, in the larval stage tunicates are tadpoles, with dorsal nerve, a notochord, at tail, and skeletal muscles that power them through shallow tidal flats.

Of 3,000 known tunicate species, there are about a dozen tailless species, and that taillessness arose independently 5 times.

Now it turns out that a single gene, called Manx, controls the formation of the tail in tunicates.  Manx is a regulatory gene.  All tailless tunicates do not express Manx, all tailed ones do.  If Manx is turned off artificially by giving antisense DNA for Manx to tunicate embryos, then the tail does not develop.  This recreates the evolutionary changes that led to the tailless species of tunicates.  Once more we have evolution in the lab.  There is some circumstantial evidence that there is even another regulatory gene further up the pathway that regulates Manx production.

We'll see whether or not the evolutionary trees are rewritable if they ever need a major rewriting.

As for the Manx thing, that merely shows that tails can be switched on and off.  Curious way for them to evolve if you ask me.

Jerry Smith · Jan 27, 2003

As for the Manx thing, that merely shows that tails can be switched on and off. Curious way for them to evolve if you ask me.

Almost any develompental feature must be switched on at some point during development by regulatory genes. You can't grow eyes and the skull they are embedded in at the same time. When working with genes, what can be switched on (at some point in development) can be switched off (permanently), if the switching mechanism is changed by mutation and fails or operates differently.

Rize · Jan 27, 2003

Originally posted by Jerry Smith
Almost any develompental feature must be switched on at some point during development by regulatory genes. You can't grow eyes and the skull they are embedded in at the same time. When working with genes, what can be switched on (at some point in development) can be switched off (permanently), if the switching mechanism is changed by mutation and fails or operates differently.

Right, because of the way organisms grow.  Which just highlites the incredible complexity of life.

Jerry Smith · Jan 27, 2003

And, especially in view of embryology, highlights how each "newer" developmental feature is always added on to the top of "older" develompental features.

Rize · Jan 27, 2003

You don't mean the thing about how we grow through the fazes of past evolution and have gills and all do you?

That's been thoroughly discredited according to AiG (even among scientific circles) (but it was in my college Biology text 4- years ago!)

Anyway, where else would a new feature be added?  And in a gradually developing embryo, things are going to occur in sequential nature obviously.  So I'm not sure I follow you.

 

Jerry Smith · Jan 27, 2003

Yes and no. The embryological evidence for evolution (or the evolutionary explanations for developmental biology, as the case may be) is very interesting. Newer adaptations are built upon older ones according to evolution, and this pattern is also seen in the developmental sequence of embryos.

Ontogeny Recapitulates Phylogeny is a long falsified theory popularized in the late 19th century, and promoted by fudged drawings of embryonic development by Earnest Haeckel. Creationists sometimes confuse evolutionary explanations of embryological phenomena with this falsified theory in order to dismiss the embryological data (and in hopes that people will think the embryonic illustrations or photos in their Biology textbooks are Haeckel's fudged work - whether they actually are or not..)

It is true that science managed to forget that Haeckel was discredited for some time, and that his drawings were erroneously used for a long time in textbooks. Another scientist (no, not a creationist) re-discovered this, and got the word out, after which most textbook publishers quickly switched to more correct illustrations or to micrographs.

To learn about the embryological evidence for evolution in general outline, see this link from Talk Origins:
http://www.talkorigins.org/faqs/comdesc/section2.html#ontogeny

You will see the reason your textbook had a section on embryology.

You can also see more about the Haeckel controversy on Kenneth Miller's web page. He is one of the writers of a very popular biology text and has a unique perspective on it.

http://www.millerandlevine.com/km/evol/embryos/Haeckel.html

Rize · Jan 27, 2003

Originally posted by Jerry Smith
Yes and no. The embryological evidence for evolution (or the evolutionary explanations for developmental biology, as the case may be) is very interesting. Newer adaptations are built upon older ones according to evolution, and this pattern is also seen in the developmental sequence of embryos.

Ontogeny Recapitulates Phylogeny is a long falsified theory popularized in the late 19th century, and promoted by fudged drawings of embryonic development by Earnest Haeckel. Creationists sometimes confuse evolutionary explanations of embryological phenomena with this falsified theory in order to dismiss the embryological data (and in hopes that people will think the embryonic illustrations or photos in their Biology textbooks are Haeckel's fudged work - whether they actually are or not..)

It is true that science managed to forget that Haeckel was discredited for some time, and that his drawings were erroneously used for a long time in textbooks. Another scientist (no, not a creationist) re-discovered this, and got the word out, after which most textbook publishers quickly switched to more correct illustrations or to micrographs.

To learn about the embryological evidence for evolution in general outline, see this link from Talk Origins:
http://www.talkorigins.org/faqs/comdesc/section2.html#ontogeny

You will see the reason your textbook had a section on embryology.

You can also see more about the Haeckel controversy on Kenneth Miller's web page. He is one of the writers of a very popular biology text and has a unique perspective on it.

http://www.millerandlevine.com/km/evol/embryos/Haeckel.html

Nope.  My textbook had the whole fish gill story in all its glory

Must have been a poorly chosen text.

Maybe I'll look at that later.

Jerry Smith · Jan 27, 2003

I suppose you don't remember, if it has been 4 years ago, what your textbook's name & editors were, or what edition you were working from? Its easy to see "gill arches" in a textbook discussion of embryology, then later see "(adult) fish gills" on a web-site from AiG and think that they were the same story, in all their respective glories.

Rize · Jan 27, 2003

Perhaps, but no I sold the book back.

lucaspa · Jan 29, 2003

Originally posted by Rize
Right. Your confidence lies in their assumptions as well. Mine does not.

What assumptions?

Your assumption is that your interpretation of scripture is correct.

lucaspa · Jan 29, 2003

Originally posted by Rize
We'll see whether or not the evolutionary trees are rewritable if they ever need a major rewriting.

As for the Manx thing, that merely shows that tails can be switched on and off.  Curious way for them to evolve if you ask me.

Evolutionary trees have been re-written several times.  The first hypothesis was birds evolved from dinos -- in the 1860s.  This was replaced that birds and dinos shared a common reptilian ancestor. This lasted from about 1890 to 1950.  Then with new fossils the tree went back to birds evolved from dinos.

Whale lineage was re-written recently because it was found that artiodactyls were the ancestors. There're lots of lineages to be precisely defined yet.

As to Manx, it shows clearly how evolution works to make major structures: change one regulatory gene rather than 20 or 30 structural genes.  Change one of the regulatory genes responsible for trunk development and you get a tail.

There's another example in bats where the wrist bones are elongated (they are usually pretty round like in our hands).  All that happens is that the gene for BMP-2 is turned on for an extra 4 hours during development!  And that accomplishes the whole process of turning a round bone into a long bone.  A small change in the transcription factor for BMP-2.

lucaspa · Jan 29, 2003

Originally posted by Rize
Right, because of the way organisms grow.  Which just highlites the incredible complexity of life.

But it also highlights the incredible simplicity of changing those "complex" structures.  In another example, changing just one base in a regulatory gene goes from the mulitple legs of arthropods to the 6 legs of insects.

1a.  http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/vaop/ncurrent/full/nature716_fs.html  Hox protein mutation and macroevolution of the insect body plan. Ronshaugen M, McGinnis N, McGinnis W.  Nature 2002 Feb 21;415(6874):914-7 Mutate one serine to alanine and change limb # from multiple limbs of crustaceans to 6 limbs of insects.  "To test this, we generated mutant versions of Artemia Ubx in which C-terminal Ser/Thr residues were mutated to Ala. In the first such mutant (Art Ubx S/T to A 15), the first five Ser and Thr residues in the C-terminus are changed to Ala. This mutant Ubx has little limb-repression function, similar to wild-type Artemia Ubx (Fig. 3). However, the mutation of one additional Ser in a CKII consensus site (Art Ubx S/T to A 15 and 7) results in a Ubx that strongly represses embryonic limbs (Fig. 3)."

 

lucaspa · Jan 29, 2003

Originally posted by Rize
You don't mean the thing about how we grow through the fazes of past evolution and have gills and all do you?

Anyway, where else would a new feature be added?  And in a gradually developing embryo, things are going to occur in sequential nature obviously.  So I'm not sure I follow you. 

Jerry went over the Haeckel "Ontogeny Recapitulates Phylogeny" falsified theory.

However, take birds.  During embryonic development, they grow teeth in their jaws, only later to have them resorbed.  Makes no sense if birds were manufactured from the ground up, but makes perfect sense under evolution.  The carnivorous theropod dino ancestors of birds had teeth.  So embryological development made teeth. But teeth add weight which is not good in a flying creature.  So any bird that had a variation that diminished the teeth had a selective advantage.  Thus you get a second program added  to development to resorb the teeth and get rid of them.

Same thing happens in baleen whales.

Evo-devo is one of the hottest areas of biology right now.

BTW, you want to know how evolution is used today, look at the following article.  Studying evolution in order to do better tissue engineering.

Eur J Dermatol 2001 Jul-Aug;11(4):286-92

Dinosaur's feather and chicken's tooth? Tissue engineering of the integument.

Chuong CM, Hou L, Chen PJ, Wu P, Patel N, Chen Y.

Department of Pathology, Univ. Southern California, USA. chuong@pathfinder.hsc.usc.edu

The integument forms the interface between animals and the environment. During evolution, diverse integument and integument appendages have evolved to adapt animals to different niches. The formation of these different integument forms is based on the acquisition of novel developmental mechanisms. This is the way Nature does her tissue/organ engineering and experiments. To do tissue engineering of the integument in the new century for medical applications, we need to learn more principles from developmental and evolutionary studies. A novel diagram showing the evolution and development of integument complexity is presented, and the molecular pathways involved discussed. We then discuss two examples in which the gain and loss of appendages are modulated: transformation of avian scale epidermis into feathers with mutated beta catenin, and induction of chicken tooth like appendages with FGF, BMP and feather mesenchyme.

Rize · Jan 29, 2003

Originally posted by lucaspa
What assumptions?

Your assumption is that your interpretation of scripture is correct.

The previous post assumes that those "teeth" are useless.

And yes I'm assuming that I'm interpretting scripture correctly for a number of reasons, just as you assume that evolution is true for a number of reasons.

These discussions are pointless.

Arikay · Jan 30, 2003

what are those reasons? (that you have interpretted the scripture correctly).

Originally posted by Rize
The previous post assumes that those "teeth" are useless.

And yes I'm assuming that I'm interpretting scripture correctly for a number of reasons, just as you assume that evolution is true for a number of reasons.

These discussions are pointless.

Ever changing science.

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