The Laryngeal Nerve and Giraffe Evolution

Well, Merv was quite correct to say that nobody is arguing for “design from scratch”, and in the recent posts nobody seems interested in “bad design.”

That leaves your question here, of “how something was designed.” Or, if we use EC terminology, “how something was created [through evolution].” The first thing to remember is that this focus shifts the question from “Is there any sign that God was involved, given contingency, doubtful design principles etc?” to “How did God create this?” - which under most understandings of the word “creation” means that God knew what he was doing, ordering, allowing etc. For example, few people would believe that if I cut myself shaving, I have “created” a new pool of blood.

But part of my point was that even that question, “How did God create [the specific example of] the giraffe with its recurrent laryngeal nerve?” is pretty uninteresting if the answer is just “It evolved that way, somehow.” Why does the leopard have spots? “It evolved that way.” How come tigers have stripes? “they evolved that way.”

We have no idea why there are giraffes, given that Lamarck’s and Darwin’s shared idea that they needed to reach high leaves to compete has been debunked, and also the principal alternative, sexual selection.

We don’t know that it evolved gradually, because long-necked giraffes appear suddenly in the fossil record. “A gradual transition may have existed” is not evidence to me, but a hoile in the evidence requiring plugging. Andreas Wagner would probably be among those who wonder how the huge suite of special adaptations that is a giraffe could co-evolve gradually under no very obvious selective pressure. Perhaps it was neutral evolution, then - but still super-coordinated.

And in the midst of all that magic, the recurrent laryngeal nerve doesn’t take the opportunity to evolve. Knowing why might help a lot in understanding evolutionary constraints, developmental constraints - or even design principles.

As I pointed out, a direct LRLN occurs as a rare variant in humans, and so probably in other species of the thousands or millions of animals that have shared the trait. We therefore know nature can do it (and have the result survive). If there was an evolutionary advantage, then now is the ideal time to see, because the human population is no longer small, but huge (my estimnate 1/4 million “direct nerved” individuals). Natural selection of traits is far easier in large populations (as pevaquark implies), so the fcat that the trait shows no sign of getting more common somewhere implies there is no selective advantage. So logically maybe there’s a selective advantage to the conservation of the recurrent nerve form.

The trouble is that when we have no idea of the advantages or disadvantages, simply to say X or Y could have happened because an appropriate fitness landscape existed tells us nothing about how God created through evolution - or even how evolution created through evolution. It’s as useful as a historian saying that wars will be won if the circumstances are suitable, and lost if the circumstances are suitable for that outcome.

Given the wonder that is a giraffe, and the marvels that enable it to be one, it’s astonishing to me that anyone would pick on one anatomical anomaly (which works perfectly well in the giraffe as in the human), and comment on God’s non-involvement. But people do - apparently to get at some Aunt Sally “Creationists” of one stripe or another, who are held to believe that God zaps human engineering wonders into instant existence.

But Wolf-Ekkehard Lönnig, mentioned above, for example, has been far more critically conscious of the evidence of giraffe evolution than someone like Richard Dawkins, whose “how” answer is that evolving a long neck is easy, and the recurrent laryngeal nerve bad design.

Just remember how Lamarck and Darwin’s “giraffes evolved to reach high food” was taught to all of us at school as a classic example of natural selection until, a relatively short time ago, somebody actually studied the giraffes instead of the theory, and found the story was false.

Final point in a rambling collection of points: what is true in considering the “evolutionary creation” of the recurrent laryngela nerve - that is, “How did God achieve this end?” also applies to the original subject of this thread. If the human reproductive system is “badly designed”, then evolutionary explanations for that achieve nothing if one believes that “God creates through evolution.” If some things have evolved “badly”, then God creates through a badly designed evolution, or God creates only certain things through evolution, the rest being beyond his control, or God does not create through evolution at all.

If someone wants to exclude certain things from the EC “process”, they’d better be able to define criteria for whih bits are God’s, and which not, and justify that “two creator” position somehow.

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Here’s one stab at the question from recent times:
http://rsos.royalsocietypublishing.org/content/2/10/150393

And figure 5 from the paper:
imagehttp://rsos.royalsocietypublishing.org/content/royopensci/2/10/150393/F5.large.jpg?width=800&height=600&carousel=1

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If you can excuse what may be a dumb question from a non-specialist: What happens if one of the 0.004% “direct nerve” population marries (as they nearly always would) a “normal meandering nerve” spouse? Do their children get the “direct nerve” variation? Or does it depend on whether something is dominant / recessive and could go either way? In other words – does the direct nerve variation pass to kids only if two “direct nerve” folks happen to marry each other? [My retention from rudimentary high school biology 35 years ago is really quite atrocious, so after you finish laughing --just indulge me please. Thanks!]

I would be surprised if anyone could answer that question, as the only way we know if someone has the variant is by surgery or autopsy. I doubt that anyone has studied the mode of inheritance. Maybe you could tell by MRI, but unless looking specifically for the nerve, would usually not be commented on by the radiologist. I suspect this is also quite neutral so doubt any advantage reproductively.

Yes - an interesting paper. It’s particularly interesting puzzling out exactly what they’re trying to show, since the actual fossil record, I believe, is complete enough to measure the actual neck length of the giraffes, in which there is not a gradual transition. So it looks more as if they’re studying some characteristics in the clade predisposing to the dramatic length of Bohlinia and the true giraffes.

As they say:

The extinct taxa in question are not direct ancestors to the giraffe, yet their neck structure provides intermediate stages culminating in the extraordinary elongation of the G. camelopardalis neck.

That’s significant, because it is not saying that necks are getting longer and longer until we finally reach the big guys. To show this clearly, within the true giraffes Giraffini (ie after all these other branches have split) is Mitilanotherium, which as one can see from the pic is still relatively short necked:

So in the scheme of things it looks more as if we’re seeing some kind of “orthogenetic rule” within that clade, something like Gould’s rule about antler length with increasing size in deer, rather than an adaptive feature, or the result of sexual selection, etc. And so we really still don’t know much about why the giraffe is so tall, nor about how the trick was done.

But if the paper is correct, there are patterns of vertebral change specific to this group that give it the potential to generate giants… provided all the other physiological changes move in step with vertebral lengthening. In an Evolutionary Creation context, that might indicate some rather non-Darwinian forethought, or short-scale frontloading, or however one wishes to describe it (sadly EC seems to lack a vocabulary for the “creation” side of the equation.)

I agree with you, Phil - which shows again there’s nothing much wrong with the canonical pattern.

But if there were an advantage, it’s hard to believe that evolution would be held up for several hundred million years because it could only do the necessary gene in a recessive flavour. The whole idea of convergence is that there is always more than one way to skin a cat (how many times have image forming eyes evolved?).

Maybe another angle to consider is that (for reasons unknown) the recurrent laryngeal nerve appears to be part of that fixed bauplan of vertebrates, the theme around which all the variants revolve, rather than the optional features which vary widely.

Thus the basic vertebrate homologies are largely impervious to adaptation (and similarly for each invertebrate taxon). You can make a ridiculously tall giraffe, an elephant with a trunk, a pterosaur or a mole and they’re poles apart in adaptation. But they have the same pentadactyl limbs, the same basic skeleton, and so on - and the same cranial nerves, of which package the LRLN seems a part.

That seems an interesting question to me far beyond its being evidence for common descent or evidence of bad design. A bit of work on that 0.004% and why they’re not taking over the world (or those polydactyl American tribes) might help reveal why there are phyla at all.

I tend to think this is the case. I remember from way back the development of the aortic arch and heart and how the nerve was caught in the curve as the heart turned and folded. I looked on youtube to see if there was a good animation, but could not find one.
My groups cadaver in med school had a mass of hilar nodes from a presumed lung ca. making dissection impossible, so sort of on my mind as we speak of these things.

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I guess I view it differently. Evolution offers a pathway to investigate how these changes happened. For example, we can find the genes responsible for neck length and look for amino acid substitutions (or changes in regulatory sequences) that were under selection in the giraffe lineage. I would agree that we need to be careful not to take a pan-adaptionist stance (i.e. everything was produced by positive selection), but the theory of evolution holds the only way of testing ideas, at least that I can see.

Given the tiny, tiny portion of the fossil record that we have searched I don’t see how anyone can make statements based on fossils we don’t have. At one point, modern humans also appeared suddenly in the fossil record. Now we have a smooth gradation of hominid fossils going back millions of years.

It hasn’t evolved in any mammal lineage that I am aware of. I did some quick reading on the evolutionary history of the pharyngeal arches, and they go back a long way.

“However, it has now been established that a key event in vertebrate pharyngeal development is the outpocketing of the endoderm to form the pharyngeal pouches. Significantly, outpocketing of the pharyngeal endoderm is a basal deuterostome character and the regulatory network that mediates this process is conserved. Thus, the framework around which the vertebrate pharyngeal apparatus is built is ancient.”
Graham and Richardson (2012)

The most ancient steps in a developmental pathway are usually harder to change through evolution, although it isn’t a hard and fast rule but more of a trend. The arrangement of nerves and pharyngeal arches is very, very ancient so it isn’t a surprise that it is strongly conserved.

If you know of any published reports on this I would love to read them. It sounds really interesting.

This goes into theological realms that I usually leave alone, but I will make one comment: Biology works. It EC is true, then it would appear that perfectly designed organisms is not the purpose of the Universe. From my understanding of christian theology and theism in general, religion seems more focused on the spiritual realm than the physical realm so I don’t think the wonky designs found in biology pose much of a problem.

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Agree Phil - and then that 0.004% bucking the trend show it can escape - but doesn’t.

Nah - it’s just intrinsically unlikely that we are the only species to develop such a variant. It’s no more speculative than a missing fossil sequence! :grinning:

No - disagree with that interpretation. The physical realm is the realm to be transformed by the resurrection: Jesus did not abandon the physical, but re-create it.

Accordingly the physical world is a good creation, reflecting the mind and deity of the Creator. That does not mean “perfect” in some theoretical way, but it does mean the it’s the work of a craftsman (a metaphor common in Scripture).

Hence in some way “evolutionary creation” needs to be understanding how evolution is doing the work of the Father God who works all things towards their good ends, and towards his good purposes.

I was more curious in papers describing this variation in humans and how common it is. Also, if there has been any work on figuring out if it is heritable. More curiosity than anything else.

Thanks for your response, and I will gladly add your views to my understanding of what christians believe. Like I said, I try to stay away from a situation where an atheist is telling a christian what their theology should be.

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It’s probably got me curious too. if I find anything I’ll let you know. I know that it’s sometimes present in situs inversus (heart on the right etc), but that’s cheating!

All I found was the original source (I believe) of the 0.004% figure (2 cases in 6,000 some surgeries):
https://www.ncbi.nlm.nih.gov/m/pubmed/3057672/

Here is another separate report of 6,000 some surgeries that had no reports, perhaps suggesting the figure is less than what the 0.004% suggests but the right side seemed consistent:
https://www.ncbi.nlm.nih.gov/m/pubmed/15175898/

That paper is really interesting. It seems that there are abnormalities with the development of the circulatory system that go along with the nonrecurrent laryngeal nerve. It seems to indicate that changes in the development of arteries is linked to the development of the nerves in those regions. This all circles back to the evolution of pharyngeal arches and how they govern the embryonic development of vertebrates.

As an interesting side note, the thyroid and parathyroid glands appear to have evolved from gill arches found in our fish ancestors.

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Here is an article that some might find informative:

“For years, there has been scant fossil evidence showing how the giraffe evolved to have such an admirably long neck. But now, the remains of a 7-million-year-old creature with a shorter neck provides proof that the giraffe’s iconic feature evolved in stages, lengthening over time, a new study finds.”

Once more an interesting article when you check the details. Here’s a phylogeny of the giraffids:

You’ll see the Samotheriinae, of which S major is a member at 7m years, branched off from the Sivatheiinae which in turn branched from the Bohlininae, with only two known genera. Here’s Bohlinia attica, compared to another Samothere:

Bohlininae, you can see, branched off from the group containing the true giraffes. Of these, the oldest member - of around the same age as Samotherium (or possibly 1-2 million years older), but only a distant cousin, is Giraffa jumae - the tallest giraffe ever found. All known members of the Giraffinae are long-necked.

So I’m having trouble understanding how Samotherium major, from a sister-group of that containing the tall Giraffinae, via the tall Bohlininae, gets to be an intermediate between the short and tall giraffids: it’s in an evolutionary line long separated from the giraffes, and significantly later than the earliest members, which are as tall as modern ones.

According to another (2017) paper:

The new post-cranial material referred to Giraffa indicates that the skeletal morphology of the genus has been relatively consistent over the past 9 million years.

I don’t see why that’s hard to understand. Is there something about biophysics or embryonic development that makes these morphological divergences particularly remarkable? Even if that lineage stands out phylogenetically (I’m not sure it does), why would we find the morphological changes extraordinary? I don’t get it.

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What I pointed out as remarkable is Samotheium as an intermediate form when in in a different clade entirely, and is preceded in time by tall forms in the groups of interest.

Yeah, but why is that remarkable? Biophysics? Development? I know both of those fields and it’s not remarkable at all from either of those perspectives. I mean, biology is always cool and remarkable, but mammals changing their forms is not remarkable; if anything, the opposite is.

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The term “intermediate” refers to the physical features of the species, not their placement in a direct lineage. Transitional and ancestral are two different things, so they shouldn’t be confused. A transitional fossil is simply a fossil with intermediate features or a mixture of features from two other taxa. As Darwin explained:

“In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition.”–Charles Darwin, “On the Origin of Species”

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