Is there a transitional in princple for these hearts?

The ability to heal after injury implies somewhere in the organism is information to make copies of the injured parts, thus it is not unusual that a little tweaking or mistake will cause a duplicate organ. This is well known, and we don't need developmental biologists tweaking genes to get these effects. The malformed duplicate can be explained as a failed healing or regeneration process or copying mechanism that went awry. Simple examples in nature: 1. flat worms, split its head, it grows two of them http://www.britannica.com/EBchecked/topic/495880/regeneration/63692/Flatworms 2. plants and trees, prune them and copies of the leaves and branches continue, but this is natural and common 3. the fourth leaf in a clover http://en.wikipedia.org/wiki/Four-leaf_clover even 5,6...56 4. some sad examples in humans, I feel sorry for those suffering, but it happens: http://en.wikipedia.org/wiki/Polydactyly http://www.urologyhealth.org/urology/index.cfm?article=51 The bottom line, even if the Cionas are viable, duplicated organs aren't examples of the transitionals I was talking about that can't exist in principle. In light of the abundant evidence of duplicated parts in nature (some natural such as in plants, and some abnormal such as in humans), the Ciona double heart is hardly spectacular and it doesn't prove transitionals of the variety I described can exist, it only proves developmental mechanisms can go awry by man-made monkeying and cause the Ciona to make copies of something it shouldn't. The researchers are overhyping the significance being able to induce defects that duplicate body parts. That's not the sort of change that create previously non existent body parts and novel rewiring (such as the double circulation with a lung and pulmonary artery). scordova

But the title of your OP asks whether transitionals are possible in principle

I'll be more specific next time which transitionals in principle I was referring to. Specifically the transitional from single-circulation to double-ciruculation such as those depicted above. It does seem, from developmental biology, there is a tremendous ability to duplicate organs with the attendant rewiring falling into place. This is sadly the case with Siamese twins or duplicated body parts. The capacity to rewire circulation on the fly seems inherent in biology, but this is not to be unexpected since rewiring on the fly happens when there is serious injury. What we may have witnessed with Ciona is an example of rewiring analogous to rewiring we see in healing. But this rewiring seems to be constrained to certain limits, not rewiring in terms of going from single to double circulation. scordova

So to “clarify the point” will you be editing the OP to note that you have now learned its principal claim has been falsified by observational evidence? That would be the proper thing to do to ensure interested persons are not misled.

Duplication of an existing organ or organ part is hardly spectacular, it is a freak. The OP dealt with the necessary rewiring to go from single- circulation to the 4 pictured double circulation hearts. In gong from single circulation to double circulation heart, there needs pulmonary arteries and then they have to be located in correctly. No pulmonary artery or mis-wired pulmonary artery and the organism is dead. But without a lung or gas bladder in the first place there is no need of pulmonary artery, but if there is no pulmonary artery in the first place (or some substitute) there is no need for a lung since the organism would be dead! That part of the OP stands, and the example of duplicating existing parts in Ciona is not directly relevant....I got drawn into a red herring discussion, and I'll know better next time how to stay my argument. The OP stands, I have to specify what intermediates specifically mean in the future, and that should clarify what I mean by lethal intermediates. scordova

But the title of your OP asks whether transitionals are possible in principle It seems the answer is yes - that transitional hearts are found in some species; that embryos remain healthy through all stages of heart development; and that a small genetic changes can lead to a functional multichambered heart in one step. It's not evidence that it happened, but it's powerful support for the principle that it could. Elizabeth B Liddle

But thanks for the correction, Sal.

You are welcome, it was the right thing to do on my part. scordova

Where does it say that this was lethal?

Nowhere. Would you prefer I say "fatal to the lineage" or will you prefer I say something like: "this proves a simple mutation in Ciona will create a new creature that lives to adulthood and reproduces and is more reproductively successful than Ciona with one compartment."

Nine percent (46/ 542) contain beating hearts with two distinct myocardial compartments within a single pericardium (Fig. 6C; Supplementary Fig. S2; Supplementary Movies S3–S6). The two compartments can function in synchrony to drive blood flow efficiently through the juvenile body cavity. The clear functional connection between these compartments is indicated by the movement of individual blood cells from one compartment into the other before exiting into the general circulation (Supplementary Movies S3–S5). The independence of the two compartments is made evident by periodic bouts of asynchronous beating (Supplementary Movies S3–S6).

Bouts of asynchronous beating? If a functioning multichambered heart had bouts where chambers weren't coordinated, this would be bad, and if it lasted for a few minutes, in certain organisms it would be fatal. The second compartment is liability, it adds plumbing that serves no purpose at best and introduces dysfunction at worst. No mention of successful maturing is provided, that omission of the eventual fate of the embryos is noteworthy. At the very least, lack of mention does not disprove the claim such variation is fatal to the lineage. scordova

Alan Fox writes,

Nowhere. There is no blueprint for an adult organism anywhere. It is all to do with local gene switches triggering cell growth, topology, local rules, cell differentiation etc. Big and growing subject.

Wouldn't the blueprint for an adult human organism be contained in the DNA? Barb

But thanks for the correction, Sal. Elizabeth B Liddle

It doesn't say that the 9% died either. They probably did, because either they ended up on a microscope slide, or ethics approval didn't allow the researchers to keep the critters beyond juvenile status, but I don't see anything in the paper that says they weren't viable. Actually, even if it did, that wouldn't be terribly important - the absolutely fascinating thing about that paper is that it suggest that a small step for a genetic sequence can be a giant step for a tunicate's heart. Hopeful monsters indeed! Elizabeth B Liddle

Where are you getting that from, Sal? I’m reading that “some” had “disorganised” hearts but 9% had a functional 2 chamber heart, instead of the usual single chamber.

9% had two-compartment beating hearts, the other 91% did not, it did not mean the 91% necessarily died, I misread, thank you for the correction. scordova

Immediately lethal for 91%, and the lethal for the remaining 9% that don’t reach maturity thus lethal to the lineage.

Lethal, lethality, unviable appear nowhere in the paper, Sal. Is there another synonym I should look for? Deadly? Fatal? No luck! Alan Fox

Where are you getting that from, Sal? I'm reading that "some" had "disorganised" hearts but 9% had a functional 2 chamber heart, instead of the usual single chamber. Where does it say that this was lethal? Elizabeth B Liddle

No, the organism wasn't viable, you're misrepresenting the actual outcome, and you have the gall to talk about misleading! scordova

scordova

CLAVDIVS: Such transitionals are observed not to be impossible in principle, and they are not lethal “in each step”, as claimed. scordova: From the link: Nine percent (46/ 542) contain beating hearts with two distinct myocardial compartments within a single pericardium. Immediately lethal for 91%, and the lethal for the remaining 9% that don’t reach maturity thus lethal to the lineage.

That is a misleading fabrication. There is not a single mention of lethality or death in the linked paper; you just made this up to try to paper over the fact this research falsifies the claim you made in the OP. The paper simply states that 9% of the experimental group developed a heart with two chambers that "can function in synchrony to drive blood flow efficiently through the juvenile body cavity".

scordova: Of course, if you coordinate several changes simultaneously to get a viable organism — that’s hardly small gradual change! We call those hopeful monsters. But I’ll clarify the point in the future. Thanks for the criticism.

Well thank you for the thank you. Of course, the paper makes it quite clear that several coordinated changes are not required, just a change in the Ci-Ets 1/2 transcription effector from symmetric to asymmetric activation, which leads to the heart forming multiple chambers. In any case, whether one or more simultaneous changes is required is irrelevant to the fact that this research blows the OP completely out of the water with regard to the claim that transitions from single- to multi-chambered hearts is impossible "in principle". What is more, there are many more examples of research showing such transitions "in principle" - for instance, several reptile's hearts are transitional between 3 and 4 chambers, some having partially connected ventricles, and some having a single ventricle with an adjustable wall. We also know the important role played by a common genetic program (e.g. T-box transcription factors) in embryonic heart formation in all vertebrates So to "clarify the point" will you be editing the OP to note that you have now learned its principal claim has been falsified by observational evidence? That would be the proper thing to do to ensure interested persons are not misled. CLAVDIVS

Not to worry.

Do not be concerned. I am not worried. cantor

OK, fair enough. And my reference to a "half-heart" was a reference to the expression "what use is half a wing". Not to worry. If we are on the same page, cool. Elizabeth B Liddle

Of course not, Cantor, but you are missing Alan’s point, I think.

I was missing his point when his post was one word long. Read the thread chronologically Elizabeth.

it is not the case that a half-heart is as useless as a whole-heart.

Who said a whole heart is useless?? cantor

Did someone claim that?

You initially seemed to be claiming that, when you make your one-word post.

My point was as CLAVDIVS elaborated on.

His post was number 22, long after I posted "Necessity".

Development of the embryo is how we get adult organisms.

That is not a controversial statement.

Variation in development, itself subject to genotypic variation and selection, will result in variation in the adult.

Neither is that statement, under a charitable interpretation of "genotypic variation and selection". cantor

You argued that changes in development will rearrange parts, but that’s not the same as saying the rearrangements will necessarily lead to a functionally viable lineage.

Well, I wasn't really making an argument, just pointing out the common misconception that evolution acts solely at the level of the adult. Obviously we then have the problem of intermediates, as per your example of going from numbers of chambers in discrete steps, which would indeed start to look like Goldschmidt-style saltation. Combine breeding isolation, neotony and embryology and there is more scope. Alan Fox

Alan Fox: Did someone claim that?

You said embryology in comment 2. Mutations affecting embryo development may re-arrange parts of an organ, but that doesn't imply the rearrangement is viable or selectively advantageous. You argued that changes in development will rearrange parts, but that's not the same as saying the rearrangements will necessarily lead to a functionally viable lineage. Problematic to the Darwinian thesis is that the defective mutant will somehow survive selective elimination to get some more defects and somehow survive even more selective elimination, and then get some more defects that make it selectively advantaged. :shock: But for that to happen, the thing has to remain alive in the first place! The experimenters have proven a lot simultaneous coordinated changes are indicated just to make a viable adult, but coordinated changes are anything but Darwinian, they are hopeful monsters. And even supposing a transitional lives to adulthood, it's defective organs are selectively disfavored. Allan Miller at TSZ put it well:

It is sufficient that NS does not act too strongly against, not that it must act for, a particular change. ”

Wrong, it is necessary, not sufficient. But right in that Darwinists have to hope NS actually doesn't work for evolution to happen! scordova

But you are speaking as to what you feel “should” be there and not giving evidence of species, that lived to pass on the novel mutation of the heart, at varying incremental stages.

You are asking detailed scientific questions which is good. However there are better places to get the current state of evo-devo research. Most working scientists don't post here either because they can't or because it's like knocking your head against a brick wall. Being a laymen, myself, and not knowing your level of expertise, I hesitate to make any recommendations, though here is an on-line journal that might put you on the track. Alan Fox

scordova @ 37 Thanks for the response. I posted that information purely to rebut the claim in the OP that the transition from a single-chambered to a multi-chambered heart was impossible “in principle” because the “transitionals would be lethal in each step”. Such transitionals are observed not to be impossible in principle, and they are not lethal “in each step”, as claimed.

From the link:

Nine percent (46/ 542) contain beating hearts with two distinct myocardial compartments within a single pericardium.

Immediately lethal for 91%, and the lethal for the remaining 9% that don't reach maturity thus lethal to the lineage. And even then, the experimenters need at least a few coordinated simultaneous changes to the creature. Of course, if you coordinate several changes simultaneously to get a viable organism -- that's hardly small gradual change! We call those hopeful monsters. But I'll clarify the point in the future. Thanks for the criticism. scordova

However, what it does tell us is that what might seem to be big discrete step between one kind of heart and another, with no viable incremental points is not a safe assumption. And indeed, in modern organisms, we see lots of kinds of hearts, on a continuum from simple to complex (as is the case with eyes as well). So that alone is evidence that each of those hearts can be (and is) viable in an adult animal.

But you are speaking as to what you feel “should” be there and not giving evidence of species, that lived to pass on the novel mutation of the heart, at varying incremental stages. Feels as though there is much question begging going on. REPOST EDIT: Forgive my previous typo in formatting. TSErik

Try upping the old reading comprehension, and give it another go by addressing the actual point.

Indeed a fault of mine. Help me out by restating "the actual point" if it wasn't about evolution of hearts. Alan Fox

However, what it does tell us is that what might seem to be big discrete step between one kind of heart and another, with no viable incremental points is not a safe assumption. And indeed, in modern organisms, we see lots of kinds of hearts, on a continuum from simple to complex (as is the case with eyes as well). So that alone is evidence that each of those hearts can be (and is) viable in an adult animal. But you are speaking as to what you feel "should" be there and not giving evidence of species, that lived to pass on the novel mutation of the heart, at varying incremental stages. Feels as though there is much question begging going on. TSErik

Of course not, Cantor, but you are missing Alan's point, I think. A human zygote remains viable throughout the developmental process. Therefore it is not the case that a half-heart is as useless as a whole-heart. Now, clearly, a human zygote and beyond to baby-hood is not a self-sufficient animal, so you are right to object that this does not indicate that a half-heart would be viable in an adult. However, what it does tell us is that what might seem to be big discrete step between one kind of heart and another, with no viable incremental points is not a safe assumption. And indeed, in modern organisms, we see lots of kinds of hearts, on a continuum from simple to complex (as is the case with eyes as well). So that alone is evidence that each of those hearts can be (and is) viable in an adult animal. Elizabeth B Liddle

A human zygote developing into an adult human has not been demonstrated to be a neo-Darwinian macroevolutionary process.

Did someone claim that? Must have missed it! My point was as CLAVDIVS elaborated on. Development of the embryo is how we get adult organisms. Variation in development, itself subject to genotypic variation and selection, will result in variation in the adult. Alan Fox

Necessity?

A human zygote developing into an adult human has not been demonstrated to be a neo-Darwinian macroevolutionary process. cantor

Then where is it?

Nowhere. There is no blueprint for an adult organism anywhere. It is all to do with local gene switches triggering cell growth, topology, local rules, cell differentiation etc. Big and growing subject. Alan Fox

Alan Fox:

Much as I had a soft spot for John Davison, I was never swayed by saltation!

You are swayed by your own personal issues, Alan. Evidence means nothing to you. Joe