The Laryngeal Nerve and Giraffe Evolution

(Jon Garvey) #30

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.

#31

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.

(Jon Garvey) #32

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!

(Matthew Pevarnik) #33

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/

#34

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.

#35

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.”

(Jon Garvey) #36

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

Strict-consensus-of-27-most-parsimonious-trees-with-the-phylogenetic-position-of
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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:

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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.

(Stephen Matheson) #37

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.

(Jon Garvey) #38

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.

(Stephen Matheson) #39

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.

#40

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”

(Jon Garvey) #41

True - but then such intermediates are of no relevance to the question of transitions. If one were interested in a gradual transition in cranial capacity from Homo erectus to Homo sapiens, it would be of no interest that one species of Australapithecine had an intermediate cranial capacity.

In the case of the giraffe, we know that living okapis have short necks and living giraffes have long necks. We also know that fossil giraffes older than Samotherium major had necks as long as today’s. Some taxonomists even suggest that the earliest true giraffes may fall within the range of the present species. And that long and short necked forms coexisted for millions of years.

So the presence of a not-quite-so-short neck in one species of Samotherium gives no indication whatsoever that that trait existed at its divergence from the giraffes several million years before. Given the shorter necks of other, older, species in the Samotherium genus, in fact, it makes it vanishingly unlikely.

#42

[quote=“Jon_Garvey, post:41, topic:39069”]

We don’t even know if a specific H. erectus skull is ancestral to any living humans. H. erectus also coexisted with later species within Homo. It would seem that H. erectus holds the same position as the intermediate giraffe species. I would agree that they need to find earlier examples of the transitional species, but the facts are that there were giraffes that had intermediate morphology.

(Mervin Bitikofer) #43

So ‘intermediate’ then, has at least two broad meanings: 1. morphologically in between in terms of characteristics, and 2. genealogically in between by descent.

Most people have #2 in mind when they are casually speaking of “transitional fossils”, but this may betray the common misconception of evolution as a long linear path rather than a branching bush. Yet #1 can be as vague as noting that a bird is an intermediate (by size) between a gnat and a watermelon, which of course has nothing at all to do with evolution. But knowledgeable paleontologists aren’t being so vague as all that when they do speak of transitional forms. So would it be fair to say they are making use of an (transitional!) definition between #1 and 2?

By noting that there are vaguely intermediate forms of ‘giraffe-like’ animals with shorter or longer necks, they are noting the presence of many expected ‘twig-like’ branches of ancestry that might be expected to share some characteristics but not others. The fossils finds of actual direct lineage over long spans of time would have to be infinitesimally small – like the chances of one set of random bones being the great-grandparent (of some degree) of another randomly found set of bones. Is that a fair take-away?

#44

I think the important point is that the intermediate nature of physical characteristics is independent of ancestry. Even if common ancestry were not true you could still find intermediate features. We conclude that common ancestry is probably true because intermediates fall into the predicted nested hierarchy which is why paleontologists link intermediate features with ancestral relationships.

Another good example is Tiktaalik roseae which was portrayed as a side branch of the tetrapod lineage in the first papers that described the species.

The biggest take-away is that the information contained in a fossil can not tell us who its parents or offspring are. Only DNA evidence can really tell us about direct ancestry. Paleontologists have been guilty in the past of describing a fossil as being a direct ancestor, so that also causes some confusion. However, even Darwin recognized that we can’t really determine if a fossil is a direct ancestor and that sister taxa can still provide important information about the past evolutionary history of the direct lineage.

(Jon Garvey) #45

It seems to me that it’s easy to take a reasonable suggestion of Darwin’s and stretch the logic to breaking point.

If, for example, there’s a trend amongst a number of genera of elephant-like creatures to develop trunks, then to find a medium length and full length trunk in different genera, both of which end up with long trunks, is a finding that can justly be generalised to the other genera.

Likewise, I suppose. a trend towards single toed horses need not deal specifically with ancestors.

But Samotherium, as a genus, is long separated from the giraffes, is of a completely different build,has a different geographical distribution, lived contemporary with long-necked true giraffes, and has no known long-necked descendants.

#46

The platypus is long separated from point of divergence between monotremes and the marsupial/placental branch of the mammal tree. The platypus also lives concurrently with both marsupial and placental mammals. However, the platypus can still provide information about that common ancestor and the transition between earlier reptillian morphology and later mammalian morphology. A species with fur and rudimentary mammary glands that lays leathery eggs from a cloaca is evidence for the transition between earlier reptiles and later mammals. The same logic holds for Samotherium.

#47

Is it your belief that the giraffe did not evolve?

(Jon Garvey) #48

No - my point is about the quality of evidence. Evidence should drive theories, rather than the reverse.

#49

But there is no Theory of Evolution for Giraffes. There is just a Theory of Evolution. And it applies to every living thing…