How do you know that digesting cellulose is the main function of the appendix? Or the first function that evolved, for that matter?
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Previously it was thought that the sack-like rabbit appendix served primarily as a reservoir for the bacteria involved in hindgut fermentation. That explanation, however, did not account for the absence of an appendix in other animals with similar digestive systems or for its presence in humans.
Blockquote Does the appendix serve a purpose in any animal? | Scientific American @pevaquark:
Both my comparisons to cancer as well as the brain were to drive home that some assumptions are wrong.
1)An organ susceptible to sickness is useless.
Cellulose digestion is the major function of the appendix.
It can happen two ways as far as I see.
convergent evolution.
on and off switches in the genome. (In which case nothing is truly vestigial).
Option 2 sounds a little Lamarckian. I thought the paper was referring to option 1. Can you share which part of the paper you are referring to?
So the paper still supports Common Descent even if the appendix is not vestigial. There are further references to papers supporting the idea of ‘constitutional responsiveness’ but I haven’t had time to chase them down.
I know the paper supports common descent even though the appendix is vestigial. Never claimed otherwise.This entire chain of discussion happened because i mentioned in passing that the appendix was not vestigial and people here disagreed with me strongly.There were even references to being influenced by “anti-evolutionary” creationists…
‘‘constitutional responsiveness’’ is an interesting term: it refers to the “ïnherited ability to respond to environmental variation.”
Recurrent phenotypes is the phenomenon of the phenotypes being found (in this case the appendix) across the evolutionary tree. I found a good paper to explain the phenomenon. i will quote some interesting information and the source.
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Recurrent evolution has most commonly been studied at the level of organismal phenotype (fig. 2), comprising an extremely rich field with hundreds of articles spanning three centuries exploring a wide diversity of recurrent phenotypes and lineages (Scotland 2011). A central concern of phenotypic work has been understanding the physical or genetic causes for recurrence. This pursuit often focuses on distinguishing between convergent evolution and parallel evolution (a distinction which itself has been extensively debated; Arendt and Reznick 2008; Scotland 2011). Generally, the distinctions follow etymology: parallel comes from the Greek for “beside” + “each other” (Παρα + αλληλος) and thus involves lineages with initially similar starting points arriving at similar endpoints by taking similar paths; on the other hand, convergence comes from the Latin for “with or together” (com-) and “to incline, tend toward” (vergere) and thus generally involves lineages with different starting points taking different paths to arrive at similar endpoints. For instance, one proposed distinction between parallelism and convergence focuses on the starting points for the two lineages: whether similar (closely related species, parallel) or different (distantly related species, convergent). Another proposed distinction focuses on paths (the specific genetic mutations underlying the changes) taken by the two lineages—whether the same (parallel) or different (convergent) (Arendt and Reznick 2008). Importantly, the two proposed distinctions are related since, because of their higher genetic and developmental similarities, closely related species are more likely to evolve similar traits by identical genetic changes than are species with more disparate biology (although this is not always the case; Arendt and Reznick 2008).
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This drawing will give you an idea what they are talking about.
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Recurrent evolution of the same genomic characteristics suggests predictability of evolution, elucidating the rules of genome evolution by revealing commonalities of evolutionary forces experienced across disparate lineages (Conway Morris 2009). We believe that the wealth of recurrent genomic features indicate unappreciated similarity of fundamental forces across lineages. Although the large number of genomic characters and finite nature of sequence space implies that genomic recurrence may sometimes occur simply by chance (see below), many cases have now been unearthed that suggest specific forces driving genome evolution down similar paths in different lineages. Identifying and understanding these forces or causes are perhaps the major challenge of the study of recurrent genome evolution.
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There is a difference from suggesting change driven by random events as opposed to change directed by “Laws of nature”. I find this paper and line of investigation very very interesting.
Really? This is what one of the authors would think of what you said:
“The creationists have misinterpreted, either mistakenly or deliberately, our work,” Laurin says. “I was horrified when I found out what they wrote about my paper. And since I’m the author, I can tell you it’s a very severe misinterpretation when they stated that our results indicated that the appendix had no evolutionary pattern.”
What do you think of Laurin’s statement?
All in all, what is your main point at this point? What is your hypothesis? What justifies your analysis of a single statement in a paper to be more valid than multiple authors with doctorates in relevant fields that spent years analyzing data?
The great differences in evolutionary rates, and especially the high evolutionary rate of the cecal appendix in Euarchontoglires, support our earlier suggestion (Laurin et al.,2011; Smith et al.,2013) that this character is a recurrent phenotype. It is particularly recurrent within Euarchontoglires, with numerous transitions in rodents and primates, and it is essentially ubiquitous in lagomorphs. Interestingly, the heterogeneous pattern of this recurrence appears to be explained better by the phylogeny than by the ecological factors tested.
The appendix does appear is nested hierarchies determines via other means with a few interesting appearances. If you reject nested hierarchies, then you don’t have any argument to begin with I think.
As for the appendix being vestigial, that’s hard to say. For the 12 species who lost the appendix it certainly was for them for a time before it was gone altogether. And while it serves some purpose for humans, it’s hard to imagine it faces any selection pressure for us anymore (though it clearly once did as the paper establishes very well- the appendix is NOT vestigial for mammals as a whole and has some use for us, but for many mammals they lost it entirely as it was vestigial and then disappeared).
Also, that’s my fault entirely. I apologize for my presumption. The appendix and vestigial structures/genes in general as misunderstood and misused by many anti-evolutionary creationists (I notice you put it in quotes most likely because you reject the possibility of being an evolutionary creationist). I wrong assumed you were just parroting their common arguments.
Recurrent phenotype means that the phenotype/trait evolved independently again and again… i.e, they did not share the trait with a common ancestor.
The evolutionary mechanisms by which this is supposed to have happened is convergent evolution and parallel evolution.
This kind of conclusion can be arrived at only if the re-emergence of the trait cannot be explained in terms of inheritance from a common ancestor.
To paraphrase …
The authors are claiming the same… and they believe it happened by evolutionary means.
The paper does point to an “evolutionary pattern”- That of recurrence…
I dont know about creationists, but i certainly would question the “random” nature if this recurrence.
The top part of the figure was the 2013 paper showing 5 appearances of the appendix and then inherited. The updated paper was corrected- there was only one appendix appearance in this clade and it was inherited by all the common descendants (though a few lost it).
Wrong for the appendix. The other appearances are interesting though and the reasons for them are discussed in the paper- the morphology of the appendix plays a role, but all in all there may be a deep evolutionary link (like the hox genes for fish fins and human fingers).
Can you clarify? The paper discusses what natural features led to its appearance and which things didn’t.
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Corroborating this view that the appendix has an adaptive function is the finding in this study that the appendix has evolved a minimum of 32 times in mammals.
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Have they retracted the above claim and reduced the overall no: to 1?
The figure you cited shows the appendix as having appeared 5 times. Its easy to count. Have the authors updated this finding with a different figure? The drawings in the paper i have access to look like this:
The top part shows the cecum… and the bottom half records the presence/absence of the appendix.In the drawing,Strepsirhini developed the appendix 5 times while the cecum was present throughout the clade indicating one common ancestor for the cecum.
Yes.There may be a deep evolutionary link… such a Pre-programmed code in the DNA which allows the appendix to developed as and when it is needed. We will be able to evaluate how “evolutionary” that possibility is when we get more concrete info about it.
I was saying the same thing you said. I don’t think the process of the appearance of the appendix is random. There must be some mechanism which controls the appearance and disappearance of the appendix.
Current Darwinian evolution is stochastic.However, if the appendix appears and disappears based on environmental stimuli, the mechanism is unlikely to be stochastic. There will be a clear cause and effect sequence… There must be some kind of stimuli which cause particular genes to switch on/off etc. And it will be very exciting to understand these things.
I dont reject nested heirarchies as an observation of nature. My only point is that a nested heirarchy will form only if there is a specific/well defined element of regulation applied on random changes.I dont see natural selection providing the kind of regulation (because its a tautology that is not well defined).
Look, if you accept the Laurin paper, its time to put this story to rest. There is no statistical evidence that the importance of the appendix changes based on change in diet. The environmental factors that make it necessary to have an appendix are not clear.
lets just conclude and say that there is no evidence to the claim that the appendix is vestigial in human beings.
Apology accepted. I don’t keep these things in mind. People just keep asking why i am harping on this while it really doesn’t disprove evolution… and i have to explain.
Frankly, i would love to bring this discussion on the vestigiality of the appendix to a close.
All of us seem to agree on the facts right now… we are just nitpicking on semantics (I think semantics is important. But i don’t think discussing it will be all that fruitful).
Though i did learn from the discussion. and found some interesting papers.(I am especially keen on reading up on recurrent phenotypes)
So thanks to all for that. @gbrooks9, @T_aquaticus, @jpm , @Bill_II, @AMWolfe
Because that is what we see it doing in other species. It is the same way that we know a TV full of bullet holes and incapable of displaying an image is not functioning even if it is used as a paper weight.
or my favorite example, a 12 volt power outlet in a car. Oddly shaped and awkward for a low voltage plug, a vestige of the old cigarette lighter that fit in the socket.
My car has a “No cigarette” symbol by the power plug. The plug has lost the ability to resist the heat from an actual cigarette lighter. So it must be vestigial.
Well no. Outdated, yes in a sense. But when they wrote the paper in 2013 the data did not allow them to conclude that the appendix was simply inherited from some ancestral species to that particular branch. Believe it or not, scientists, as I am when I write scientific papers, always aim to have well supported conclusions and do not claim beyond what the data says. Should they do that, there is a large body of other scientists that can help correct anything that snuck by peer review.
However, with more data they gained a more accurate understanding of what actually happened and found that it was actually just one single appearance instead of five- and in that lineage the appendix did not appear over and over again but was instead inherited through common descent.
Yes, that’s what I posted and explained what I was posting and what I just re-explained above.
Do you know what the authors mean by that?
And then to disappear when it is not needed.
Indeed. It disappears when it serves no function and isn’t preserved via natural selection. The 2017 paper describes more of the mechanisms that lead to its development.
Read the paper. Surprisingly environmental factors played little role in the appearance of the appendix from the cecum.
It serves a function. That has never been disputed. For anyone to say it doesn’t is just wrong. But many things can be repurposed- i.e. the retrovirus insertion that helped lead to the development of the placenta in mammals! However why did the appendix come about in the first place? The 2017 paper summarized some ideas but it’s function and reason it was selected for is still a little mysterious! More fun stuff to learn.
Needless to say, again- for many species that had an appendix and lost it- it was vestigial for many generations at the very least!!!
Wisdom teeth (Do ID folks ever have them removed?)
Arrector Pili: The muscle fibers that give you “goose bumps.” In animals, they fluff up fur and make the hackles rise so you’ll look big and scary, but not in humans, because our body hair is vestigial also!
I was thinking the loss of body hair was possibly to cut the parasite load. The retention of pubic and axillary hair is thought to be related to pheromone retention, but who knows.
