In response to Neil Shubin’s recent paper on the subject, and Carl Zimmer’s summary, the creationist Michael Denton criticizes evolutionary explanations for the vertebrate limb. It’s a bizarre argument.
First, here’s the even shorter summary of the Shubin work. Ray-finned fish have, obviously enough, rays in their fins — rigid bony struts that provide structure. These rays are formed dermally. That is, osteoblasts deposit bone on the surface of a connective tissue matrix to build the rods of bone that prop up the fin. It’s called dermal bone because the classic example is the assembly of bony elements within the dermal layer of the skin.
Another way of making bone is endochondral. You start with a framework of cartilage, and cells within the cartilage (which is what “endochondral” means) gradually replace the cartilaginous tissue with bone. Your limb bones, for instance, are endochondral, starting out as fetal rods of cartilage that were replaced by the action of osteoblasts.
What the researchers in the Shubin lab found is that fish fins, which have dermal bone, and tetrapod limbs, which have endochondral bone, use the same cell signaling pathways and cell movements to build the cellular structure of the limb/fin, but differ in the final steps. Fish switch on the dermal bone pathway, while tetrapods use the endochondral pathway. We have a fundamental similarity than simply uses a different end-product, which ties the assembly of fins/limbs more closely together than we had thought.
Not to Denton, though! He wants to make some strangely saltational argument that these two modes of bone formation are somehow incompatible. I’ll show you his final conclusion, so you can decide to bother with the rest.
In short, my assessment is this: There never were any transitional forms making both dermal bone and endochondral bone. Organisms made one or the other.There never were any transitional forms with fin rays and digits. And I predict that no matter how extensively the fossil record is searched, the phenotypic gap between fins and limbs will remain even as the genetic gap continues to diminish.
That’s an incredibly stupid statement. You make both kinds of bone; your skull, for instance, is largely formed of dermal bone, while your limbs are endochondral. Fish have both endochondral bones (for example, in their vertebrae) and dermal bones (skull and fin rays). The ancestral fish-like form had both kinds of bones. We have fossils of transitional forms with both a central endochondral core and fin rays.
We’re done. Denton’s claim has already been addressed and refuted. How can he not know this?
You can just stop now. His whole argument is dead in the water. But you could take a look at the thought processes that led to that stupid conclusion, and they’re kind of weird, too.
I think he has omitted some of the important and obvious challenges to the Darwinian framework implicit in this work. On any consideration, these advances (and many other similar in the evo-deco area) provide no support for the Darwinian causal framework — a long sequence of small adaptive changes unconstrained by any factors other than immediate adaptive utility — as sufficient to propel the evolution of the limb from fins.
Most changes are not adaptive. Adaptive utility is not the only constraint on change, and is often ignored by the process. Disregarding his 18th century conception of evolution, though, his logic is faulty: of course finding that the transition between two forms only requires a small number of molecular changes makes the ability of evolution to generate the new form simpler.
He even acknowledges this.
This evidence provides further support for the notion that the genotypic distance between fin and limb may be far smaller than previously envisaged. It is indeed intriguing that, as in other areas of evo-devo, the less the genetic distance across an evolutionary transition, the more the evidence for evolution grows.
Yes? So? Finding a smaller genetic difference, as Shubin has done, is increasing the evidence for evolution. What’s the problem?
But ironically, at the same time, the less room there is for Darwinism as a creative agency. Its as if the hand was already in the developmental genetics of the fin, so to speak, awaiting evolutionary expression, perhaps generated by a relatively small genetic trigger.
He’s using that creationist buzzword, “Darwinism”, but setting that aside, selection is not a creative agent anyway. There is no “hand” waiting inside the fish fin, requiring only a simple trigger to make a hand. No one proposes such a thing, except creationists.
On such a scenario, there is absolutely nothing left for the agency of cumulative selection to do. Evolution would be completely constrained by the deep homologies underlying all vertebrate lateral appendages and is just an unfolding of alternative phenotypes already inherent in these shared commonalities.
But note: fish fins and human hands hold shared commonalities, as the scientists Denton ignores keep showing, but they are different. There are accumulated small regulatory changes that shaped the hand from the ancestral fin, so there are differences as well as similarities. The fact that fish do not spontaneously develop fingers ought to tell you that there is something that evolution over time had to have done.
That’s about as much as I can take. Denton goes on and on, trying to claim that somewhere in the history of the limb there had to have been a saltatory change (which is true; a single nucleotide change is a kind of leap that can radically change a protein), and that a mutational change would have occurred without an adaptive end
(also trivially true), and therefore…evolution is false?
That makes no sense at all. Denton has some kind of bizarro version of evolutionary theory in his head that is completely lacking in chance events, to the point where he thinks even mutation must have an adaptive purpose. That version of evolution is also already known to be false, so once again he’s patting himself on the back for refuting something that no one believes.
PZ: Denton’s claim has already been addressed and refuted. How can he not know this?
That’s the core of his argument: I’m ignorant, therefore GOD! (Ominous thunder).
Whilst Denton may or may not know, I presume the choir he is preaching to both does not know, and does not care to check.
I’m reminded of a disease, where trauma also causes calcification. Utterly uncontrolled and eventually, lethal.
That said, he ignores his previous demolition of his bullshit easily enough, he ignores it.
When one ignores all counterarguments and continues unabated, pretending the previous refutations don’t exist, typical.
You can’t win, as they don’t play. Anything off message does not exist to them.
Alas, having actually conversed with such people in a social situation (where I didn’t play the asshole card, as I was quite curious), they don’t realize that they do that and they’re actually filtering out reality.
Honestly, I think it’s a form of mental illness, albeit in most, a harmless one. No, I take that back, far too many Trump supporters exist already and remain untreated. ;)
But, for every one of that ilk, Jehovah Witlesses have sent followers, then even elders to my door, where excellent conversations ensued and they eventually left the faith.
Their leadership, in continuing to send people to my door show the very characteristics of the above individual.
While I’ve railed against those who are willfully ignorant, for those, as it’s causing significant attrition of the ranks, I’ll happily accept.
wzrd1, please don’t conflate mental illness with wilful ignorance, cognitive bias, or Trump support.
@chrislawson #4:
You’re wasting your time. He’s been asked before. All we can do is sigh sadly at the repeated boasts of a man who lambasts Trump for his alleged narcissistic disorder…
I really need to use that hated TLA: LOL as being such an appropriate response to this tpyo:
laughing through the conflation of evolution with “Art Deco”
surely, it’s a tpyo for evo-devo, the abbreviation of “evolution of development”
still, hilarious to see such an error in a “scholarly” criticism of paleontology.
Not just “adaptive utility,” but immediate adaptive utility. I don’t know if there’s a word less-suited to describing evolution than “immediate.”
Hey, I come from a mammal, therefor evolution is false!
(About as sensible as Denton’s argument.)
How do you know? Where you there?
Shubin is great, FYI everyone, the 3-part Inner Fish docs that aired a while ago on PBS are available online for free (in the U.S.) at Biointeractive. They’re great especially for noobs like me, and in there it explains this topic in a very helpful visual way.
Oops, sorry. Here goes link.
I’m all for refuting the arguments of creationists but I wish PZ would refute the arguments they actually make rather than some other argument. What Denton said is that there are no transitional forms that make both dermal bone derived fin rays and endochondral bone derived digits. So the questions are 1) Is it true? 2) If it is true, is it incompatible with evolution?
Did you miss the part where he said “We have fossils of transitional forms with both a central endochondral core and fin rays”?
How does he know this. Was he there?
In this case, the usual stupid creationist question is oddly enough, relevant.
Google: Tetrapods evolved from the lobe-finned fishes around 390 million years ago in the middle Devonian Period,
1. Denton or anyone has no idea and no way of knowing how the ancestral lobe finned fish made their fin rays 390 million years ago!!! Dermal or endochondral or a mix or something different.
2. Which means his hypothesis lacks a crucial component. It isn’t falsifiable.
Probably not. We have a huge amount of evidence that evolution is true, that we are jumped up lobed fin fish, and so on. Some of the fin bones of fossil lobed finned fish are homologous with our limb and wrist bones
@ consciousness razor
A central endochondral core is dodging the point because a central endochondral core is NOT a reference to digit formation.
I couldn’t quite figure out what Shubin actually found from the OP.
The key point is in bold.
They found that ray finned fish use the same Hox genes for fins that mammals use for limbs.
And that switching from dermal bone to endochrondral bone isn’t all that difficult. Bone is bone, both made by the same cells, osteoclasts.
This is even stranger because our immediate ancestors, weren’t ray finned fish. They were lobed finned fish which branched off earlier.
@14 raven
How does he know this. Was he there?
In this case, the usual stupid creationist question is oddly enough, relevant.
Google: Tetrapods evolved from the lobe-finned fishes around 390 million years ago in the middle Devonian Period,
1. Denton or anyone has no idea and no way of knowing how the ancestral lobe finned fish made their fin rays 390 million years ago!!! Dermal or endochondral or a mix or something different.
2. Which means his hypothesis lacks a crucial component. It isn’t falsifiable.
Of course it’s falsifiable. The existence of an organism with both ray fins and digits would falsify it. What isn’t falsifiable is the idea that such an organism ‘might’ have existed in the absence of any evidence that it did.
@16 raven
Says who? Where is the evidence that it isn’t all that difficult?
Recent publications from Shubin that seem relevant to Chris61’s concerns.
A GoogleScholar page.
https://scholar.google.com/scholar?as_ylo=2016&q=neil+shubin&hl=en&as_sdt=0,14
Enjoy.
FFS, learn to read or wake up your lazy thinking brain dog.
This is what Neal Shubin and his lab found. It’s in the OP and the more extensive NYT report that I just quoted.
There never were any transitional forms making both dermal bone and endochondral bone. Organisms made one or the other.There never were any transitional forms with fin rays and digits. And I predict that no matter how extensively the fossil record is searched, the phenotypic gap between fins and limbs will remain even as the genetic gap continues to diminish.
Because god made every other part of evolution, except that.
@20 raven
No raven, that’s not what Neal Shubin and his lab found. What they found is that the cells that make up ray fins and the cells that make up digits are both derived from cells that at one point in their life express a few common genes. There is nothing in that to imply the switch isn’t difficult. There is in fact nothing to imply that a switch occurred at all.
You missed the point. Again.
Endochondral bones in fish limb cores is an evolutionary and fossil novelty.
It’s just another step to go further down the limb and make wrist bones. Which we also see.
The last step is…digit bones. You can see the progression by looking at the diagram in the OP above.
Tiktaalik, has shoulder, upper arm, lower arm, and wrist bones. What it lacks is digits.
What Shubin et al. found was the same pattern forming genes active in the same place in both ray finned fish and mammalian limbs.
Wrong again.
Ray finned fish have rays. We have fingers. Our ancestors had rays. There was a switch there and we know about when it happened from the fossil record. The molecular data gives us an idea of how it happened.
I know what your problem is. You are presuppositional creationist troll. Creationism is a religous idea that was falsified centuries ago and survives as a belief impervious to reason and knowledge.
Keep being wrong but I’m not wasting another second on an ignorant idiot troll.
@23 raven
Yes he did find that. A couple of pattern forming genes active in the same general location in both ray finned fish and mammalian limbs. Still doesn’t demonstrate that a transition between ray fins and digits is easy or even occurs at all.
For the other two people who might be following this pointless exchange.
An odd factoid which reinforces the point PZ made above. Organisms, including humans can and do make both dermal and endochondral bones.
Dermal bones don’t have to be small or platelike as in our skulls.
Our collar bones are dermal bones.
@ 24 raven
Actually I believe that nothing in biology makes sense except in the light of evolution. Creationism is certainly wrong. But what I don’t believe is that one should use shoddy arguments to support that belief.
@26 raven
ob·fus·cate
verb
render obscure, unclear, or unintelligible.
The origin of our collar bones is irrelevant to the origin of digits versus ray fins.
But thanks for playing.
Jesus. Have you even read the Nature paper?
The whole point is that the patterning system is shared, and it’s a difference in the induction at the end of the pathway.
But yeah, I know, you’re going to twist everything into something that the paper doesn’t claim and pretend that you have some insight Shubin missed. OK. Not impressed.
Chris61, please REFERENCE Shubin’s papers that YOU disagree with, and show a reference (link) to argue against Shubin. You sound like a troll if you never reference the literature supplied to you, either pro or con.
@29 PZ
Denton argues that there are no transitional forms that have both ray fins and digits. So I’ll ask you – are there transitional forms that have both ray fins and digits and if not, why doesn’t it matter?
Cthulhu, Michael Denton is writing pure gibberish.
On such a scenario, there is absolutely nothing left for the agency of cumulative selection to do. Evolution would be completely constrained by the deep homologies underlying all vertebrate lateral appendages and is just an unfolding of alternative phenotypes …
This part is correct.
Denton: already inherent in these shared commonalities. Gibberish.
There is nothing inherent in having deep shared homologies. There is no direction to evolution. Evolution is blind.
Better
In practice these deep shared homologies aren’t much of a constraint. The lobe fins have become mammal fins, bat wings, bird wings, Pterosaur wings, quadrupeds, and bipeds.
There is some channeling going on. AFAIK, no tetrapod has ever developed another set of limbs. It’s all 4 with some losing two or all 4, i.e. a few flightless birds and whales, various snakelike creatures.
Denton: On such a scenario, there is absolutely nothing left for the agency of cumulative selection to do. More gibberish Just wrong.
There is everything left for the process of cumulative selection to do. It’s done a lot in the last 400 million years since every organism in that time has been a product of…cumulative selection.
PS Michael Denton is tedious to unpack. It’s just a Gish Gallop and almost every sentence is wrong.
Why? If you learned any biology, and you have claimed to be a biologist working for ENCODE, you know the answer.
At what point in the transition does the ray fins start to be called digits.
Plus Tiktaalik has front digits and back ray fins.
Time to quit your disbelief. You are sounding like a creationist.
@31 chris61:
That’s as much nonsense as expecting transitional forms between early reptiles and birds to have both arms and wings. They have transitional arm-wings not a set of each. So the question is not if something has both fin rays and digits – I mean, Tiktaalik does so that’s already been answered, but say we were just talking about one limb – but if anything has transitional fin ray-digits.
For instance since one has endochronal bone and the other dermal bone, you would expect a transitional form to either have some sort of type with mixed properties, or to have both. And oh look, this article talks about the latter. For you to say that kind of transition is dodging the point only means you don’t understand what the point is.
Got it! Just had to find the right previous paper to explain what I was missing. Thanks for your help.
For. Crying. Out. Loud.
Shubin has written a paper that explains clearly how something happens, and all Denton can do is whine, “But why?”
It takes a conscious effort of will to refuse to accept something so obvious when it is presented like that.
It’s like someone who insists that 2 + 2 = 5, showing them two coins in your left hand and two more in your right hand making four, and then them blaming you for there not being five coins.
I think that many creationists fail to grasp that all mutations are not adaptive “changes”, but random mutations that may or may not assist an organism’s fitness in its niche in nature.
Perhaps, it’s a difficulty in comprehending the very concept of randomness, that a mutation doesn’t necessarily do anything for an organism and indeed, can be deleterious by coding for a protein that won’t function in a survivable way for that organism.
Which is, in and of itself an odd error to make when one considers known diseases, such as Alzheimer’s disease and its misfolded protein or even cancer.
But even odder, creationists ignore what humans have done with selective breeding, a prime example that I’ve used was how rapidly we bred wild turkeys into a substantially different domesticated turkey. A feat all the more impressive, as the knowledge of genetics was much less at the time.
@36 bluerizlagirl
Shubin has written a paper that shows how one step in something might have happened. As with pretty much everything in evolution, there’s still a lot of details missing. Which I suppose is a good thing for Shubin as it gives him plenty of fodder for future experiments.