Come on, pay attention and remember the thread of conversation. I said that Tbx4 couldn’t last for 50 million years both capable of functioning and unexpressed. You asked what my explanation was for atavistic limbs. I responded that the explanation is that Tbx4 is not unexpressed. And in fact if you’ve been following, it is indeed still expressed in the transient limb buds of whales.
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Where did they claim that?
Ah, so you finally admit it’s Tbx4 in extant cetaceans being expressed which produces hind limbs. That was like pulling teeth.
Huh? Throughout this thread you’ve been saying that tbx4 is unexpressed.
In the CMI article I linked to above.
CMI: " Whales do not have all the various ‘genes’ needed for making a leg."
No. I said that it was unexpressed in producing hind limbs in extant cetaceans. Not that it couldn’t be expressed elsewhere.
So where did John ever claim that the gene wasn’t expressed elsewhere? I’m bewildered by your comment about him “finally admitting” this.
He kept expressing doubt unexpressed tbx4 was responsible for cetaceans having no hind limbs. Atavistic limbs which appear due to the reactivation of expression of tbx4 show his claim was wrong.
This whole thread started because the YEC organization CMI denied cetaceans have the genes for producing hind limbs which they call “legs”. The evidence shows this claim is false as the atavistic hind limbs demonstrate. This whole “discussion” is pretty silly.
That’s possible true but misses the point. Even if they don’t have all the genes, they have some of them. Is this goal post moving?
No. The point was CMI is arguing there is no genetic evidence for whales ever having legs. That claim is demonstrably wrong. It’s the only point.
Like I said, this whole discussion is pretty silly. Some people like to argue just for the sake of arguing. 
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I will confess to extreme puzzlement here. Can anyone tell me what’s going on?
This is just plain wrong. Tbx4 is expressed in whales, normally. It may be (though I haven’t seen the evidence) that it’s increased expression of Tbx4 that causes atavistic limbs.
You contribute to the silliness when you say silly stuff. Take more care.
I don’t know what that has to do with my question about him denying that the gene was expressed elsewhere.
It’s not actually clear that tbx4 is unexpressed in the hindlimb buds, so I don’t think there’s a simple 1:1 link you can draw between unexpressed tbx4 and lack of hindlimbs.
What evidence do we have that reactivation of tbx4 expression is the cause of atavistic hindlimbs developing?
CMI claimed there is no evidence from developmental biology that cetaceans had legs.
@Timothy_Horton said this is wrong because there is a gene present commonly used in leg development and cetaceans actually have hindlimb buds for a period of time early in development. And are occasionally born with atavistic hind limbs. This makes sense if descended from terrestrial ancestors.
What is actually being disputed here? Perhaps this discussion should be nipped in the…bud.
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“Whales do not have all the various ‘genes’ needed for making a leg” is a far cry from “there were no genes for limb development present in extant whales”, as your initial charactarization claimed.
Yeah that would seem to be a fairly standard creationist position. No evidence for evolution!
Tbx4 is another piece of evidence in a larger puzzle, which considered in it’s totality confirms that whales had terrestrial ancestors with actual legs. Creationists would argue that tbx4 isn’t evidence for this because tbx4 has other functions that don’t have to do explicitly with “legs”(such as being involved in pelvic fin development in fish). Is it a “leg gene”? Well it’s a leg-gene in the sense that it’s apparently partially responsible for leg development, though it’s not only a leg gene.
But tbx4’s even wider taxonomic distribution(and the phylogeny one can derive from it) is of course evidence for the common descent of all organisms that have it. Whether it’s presence and activity result in bona fide legs or not, it’s another piece of data that corroborates the nested hierarchy.
Pointing out that has other(related) functions, and goes back to even older, deeper nodes in the phylogenetic tree, doesn’t make it fail to be evidence for the shared evolutionary history of whales and terrestrial mammals. And given cetacean’s presumed position in a rooted phylogenetic tree of artiodactyls inferred using tbx4, it is also evidence for the terrestrial ancestry of whales.
Well as long as it’s not all the time.
As pun-ish-ment? I’ll get my coat.
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Darned if I know. Someone seemed to be arguing the Creationist position for a lark.
Seemed, to you. But you don’t have a leg to stand on. You femur? Don’t forget to tibia waiter.
Well of course! Here they are clearly referring to Limb Kind. 
Would that make the appendage be a Limb of God ? 
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So badly want a counter pun … but I got mutton.
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