9 ms·

> My high school bio teacher confidently claimed that the appendix was a "useless organ". So does the Encyclopedia Brittanica, Healthline, and any number of ot

> My high school bio teacher confidently claimed that the appendix was a "useless organ". So does the Encyclopedia Brittanica, Healthline, and any number of other sources: > appendix, formally vermiform appendix, in anatomy, a vestigial hollow tube

echelon 5y ago
If the appendix truly serves no function and isn't developmentally required, then selection pressures would tend to remove it. It likely has some complex purpose, such as a reservoir for microbiome.
- theshrike79 5y ago
  The appendix is used to reboot the intestinal biome in case of a catastrophic event. It's pretty much an on-site backup for intestinal flora :)
- beebmam 5y ago
  This is a common misunderstanding. The same logic would apply to male nipples. It's a flawed logic.
  - wwwwewwww 5y ago
    Nipples are used by female mammals for feeding their young, so this logic does not apply to nipples.
    - beebmam 5y ago
      It certainly does apply: why do men have nipples? Likely for reasons similar to why we have an appendix. Fundamentally, natural selection and evolution are models that help explain general biological processes, to help us comprehend a bigger picture. Around the edges of that picture, it's not fully clear. The truth is that the universe is governed by laws that are deeply unintuitive: general relativity and the standard model. Each layer of abstraction on these makes the periphery of the image fuzzier, but allows us to make more sense of the part of the image that we're focusing in on.
      - echelon 5y ago
        Genes to turn off development of the nipples would cost more. The same body plan is used until sex hormones cause sex characteristics to develop. Many females also find male nipples attractive.
- bmeski 5y ago
  That's only if the gene's to express an appendix ever go away. I always think back to Richard Dawkins explaining how a particular vein in a Giraffe's neck is wrapped around a lower neck bone and has grown 2x to accommodate the long neck instead of regrowing in a more efficient way (not wrapping).
  - freedomben 5y ago
    I believe you're talking about the laryngeal nerve! And I don't think it's just giraffes, it's all mammals, which also points to a common ancestor.
    - roywiggins 5y ago
      The recurrent laryngeal nerve is actually common to all tetrapods, not just mammals. Birds have it, probably dinosaurs had it. https://bioone.org/journals/acta-palaeontologica-polonica/volume-57/issue-2/app.2011.0019/A-Monument-of-Inefficiency--The-Presumed-Course-of-the/10.4202/app.2011.0019.full https://bioone.org/journals/acta-palaeontologica-polonica/vo...
      - bmeski 5y ago
        Nature’s billion dollar mistake?
- bluepizza 5y ago
  > selection pressures would tend to remove it. A person born without an appendix has no actual advantage over a person who has one, so selection doesn't really influence it. The human body is full of things that truly serve no function, and it's also full of detrimental things, such as genetic diseases. As long as it does not impact reproduction, selection has no impact.
  - consp 5y ago
    > A person born without an appendix has no actual advantage over a person who has one Untreated appendicitis is quite deadly. I would say there is definitely some advantage.
    - blacksmith_tb 5y ago
      That's true, but untreated cardiomyopathy is potentially deadly too, yet that isn't enough pressure to cause us to not have hearts...
      - joconde 5y ago
        Good idea but bad example. Something needs to fulfill a heart's role, but we can live without an appendix just fine.
        blacksmith_tb 5y ago
        Oh sure, it was reductio ad absurdum, just pointing out that the possibility of appendicitis wasn't by itself an argument against its continued existence - I don't know anyone personally who has ever been diagnosed with it...
        Dylan16807 5y ago
        > just pointing out that the possibility of appendicitis wasn't by itself an argument against its continued existence Except that yes it is an argument against it. Your reduction breaks down because it conflates "a reason" with "all reasons".
- dwaltrip 5y ago
  You yourself gave the answer. “Tend to” means it is likely, not that it will always happen.
- fastaguy88 5y ago
  This is a widely held misconception. Mammalian genomes contain about 50% of their DNA as repeated sequences, and although there are people who can imagine uses for those sequences, there is no evidence that they are required or even evolutionarily advantageous. The idea that modern higher organisms have been "optimized" so that every part is essential is not well supported by evidence, and there are many examples of features that simply are historical artifacts or "not-sufficiently harmful". Many evolutionary biologists are comfortable with neutral theories consistent with the idea that large portions of the genome are not under strong (or perhaps even moderate) selection.
  - gwright 5y ago
    biological version of dead code with no time allocated in the roadmap for cleanup and refactoring?
    - frenchyatwork 5y ago
      Only vaguely. If the DNA was to be compared with our programming languages, it would be like INTERCAL, but a million times worse. Sections of the genome interact not only with the code right around them, but also with code far away, as a result of the chromosomal folding. So a section of 100 nucleotides might not do anything if you splice it out and throw various enzymes and other chemicals at it, and it might not even matter that much which nucleotides they are, but if you remove them and change the shape of the chromosome, it might not work the same way. A lot of our knowledge of genetic is limited to the things that are easy to test.
    - UnFleshedOne 5y ago
      Except our machines are designed around the idea of isolating components and minimizing unintended side effects, while biology has no such compulsion. Imagine if an extra semicolon in one of your unused files shifted electrical distribution on storage media and that had all kinds of downstream effects on unrelated systems and those effects were critical for multiple other functions. Only increase complexity enough so the whole contraption is NOT brittle.
  - 5y ago
- hinkley 5y ago
  Others have said this using different words, but evolution relies on the preservation of low-cost mutations. It took many mutations to get from photoreceptors to the mammalian eyeball. If the cost is small enough that other factors dominate your ability to procreate, it will spread to all of your descendants. If other genes in your genome make you reproductively successful, that gene edit will spread and spread. It’s a good thing these cheap changes are preserved, or viruses and bacteria would have wiped out all multicellular life early on by practicing patience. We all have genes that make us less susceptible to some pathogens than others and if a bad enough variant comes around, suddenly we are over represented in the next generation. If the hits keep coming eventually our family reunion may be the only one being held.
- elliekelly 5y ago
  Can’t an inherited trait be “neutral”? By that I mean it confers neither a benefit nor a detriment? It’s my understanding that the baby toe, for example, isn’t particularly useful anymore. But having or not having the baby toe(s) isn’t likely to help or hinder a person’s ability to reach adulthood and reproduce. There must be a lot of traits like that, right? Like eye color or maybe wisdom teeth. No one (as far as I know) is selecting a sex partner based on whether their wisdom teeth were impacted or not.
- jfrunyon 5y ago
  That's not how selection works. If something doesn't decrease survivability, then there is no reason why evolution would get rid of it.
- robbiep 5y ago
  This is a profound misunderstanding of the driving forces of evolution. Why do we have wisdom teeth? Just because something is useless doesn’t mean it’s eliminated
323 5y ago
They are wrong. > The appendix has been identified as an important component of mammalian mucosal immune function, particularly B cell-mediated immune responses and extrathymically derived T cells. https://en.wikipedia.org/wiki/Appendix_(anatomy)#Functions https://en.wikipedia.org/wiki/Appendix_(anatomy)#Functions
- neuronic 5y ago
  Do we have data on COVID in people without appendix?

echelon 5y ago

If the appendix truly serves no function and isn't developmentally required, then selection pressures would tend to remove it. It likely has some complex purpose, such as a reservoir for microbiome.

theshrike79 5y ago
The appendix is used to reboot the intestinal biome in case of a catastrophic event. It's pretty much an on-site backup for intestinal flora :)
beebmam 5y ago
This is a common misunderstanding. The same logic would apply to male nipples. It's a flawed logic.
- wwwwewwww 5y ago
  Nipples are used by female mammals for feeding their young, so this logic does not apply to nipples.
  - beebmam 5y ago
    It certainly does apply: why do men have nipples? Likely for reasons similar to why we have an appendix. Fundamentally, natural selection and evolution are models that help explain general biological processes, to help us comprehend a bigger picture. Around the edges of that picture, it's not fully clear. The truth is that the universe is governed by laws that are deeply unintuitive: general relativity and the standard model. Each layer of abstraction on these makes the periphery of the image fuzzier, but allows us to make more sense of the part of the image that we're focusing in on.
    - echelon 5y ago
      Genes to turn off development of the nipples would cost more. The same body plan is used until sex hormones cause sex characteristics to develop. Many females also find male nipples attractive.
bmeski 5y ago
That's only if the gene's to express an appendix ever go away. I always think back to Richard Dawkins explaining how a particular vein in a Giraffe's neck is wrapped around a lower neck bone and has grown 2x to accommodate the long neck instead of regrowing in a more efficient way (not wrapping).
- freedomben 5y ago
  I believe you're talking about the laryngeal nerve! And I don't think it's just giraffes, it's all mammals, which also points to a common ancestor.
  - roywiggins 5y ago
    The recurrent laryngeal nerve is actually common to all tetrapods, not just mammals. Birds have it, probably dinosaurs had it. https://bioone.org/journals/acta-palaeontologica-polonica/volume-57/issue-2/app.2011.0019/A-Monument-of-Inefficiency--The-Presumed-Course-of-the/10.4202/app.2011.0019.full https://bioone.org/journals/acta-palaeontologica-polonica/vo...
    - bmeski 5y ago
      Nature’s billion dollar mistake?
bluepizza 5y ago
> selection pressures would tend to remove it. A person born without an appendix has no actual advantage over a person who has one, so selection doesn't really influence it. The human body is full of things that truly serve no function, and it's also full of detrimental things, such as genetic diseases. As long as it does not impact reproduction, selection has no impact.
- consp 5y ago
  > A person born without an appendix has no actual advantage over a person who has one Untreated appendicitis is quite deadly. I would say there is definitely some advantage.
  - blacksmith_tb 5y ago
    That's true, but untreated cardiomyopathy is potentially deadly too, yet that isn't enough pressure to cause us to not have hearts...
    - joconde 5y ago
      Good idea but bad example. Something needs to fulfill a heart's role, but we can live without an appendix just fine.
      - blacksmith_tb 5y ago
        Oh sure, it was reductio ad absurdum, just pointing out that the possibility of appendicitis wasn't by itself an argument against its continued existence - I don't know anyone personally who has ever been diagnosed with it...
        Dylan16807 5y ago
        > just pointing out that the possibility of appendicitis wasn't by itself an argument against its continued existence Except that yes it is an argument against it. Your reduction breaks down because it conflates "a reason" with "all reasons".
dwaltrip 5y ago
You yourself gave the answer. “Tend to” means it is likely, not that it will always happen.
fastaguy88 5y ago
This is a widely held misconception. Mammalian genomes contain about 50% of their DNA as repeated sequences, and although there are people who can imagine uses for those sequences, there is no evidence that they are required or even evolutionarily advantageous. The idea that modern higher organisms have been "optimized" so that every part is essential is not well supported by evidence, and there are many examples of features that simply are historical artifacts or "not-sufficiently harmful". Many evolutionary biologists are comfortable with neutral theories consistent with the idea that large portions of the genome are not under strong (or perhaps even moderate) selection.
- gwright 5y ago
  biological version of dead code with no time allocated in the roadmap for cleanup and refactoring?
  - frenchyatwork 5y ago
    Only vaguely. If the DNA was to be compared with our programming languages, it would be like INTERCAL, but a million times worse. Sections of the genome interact not only with the code right around them, but also with code far away, as a result of the chromosomal folding. So a section of 100 nucleotides might not do anything if you splice it out and throw various enzymes and other chemicals at it, and it might not even matter that much which nucleotides they are, but if you remove them and change the shape of the chromosome, it might not work the same way. A lot of our knowledge of genetic is limited to the things that are easy to test.
  - UnFleshedOne 5y ago
    Except our machines are designed around the idea of isolating components and minimizing unintended side effects, while biology has no such compulsion. Imagine if an extra semicolon in one of your unused files shifted electrical distribution on storage media and that had all kinds of downstream effects on unrelated systems and those effects were critical for multiple other functions. Only increase complexity enough so the whole contraption is NOT brittle.
- 5y ago
hinkley 5y ago
Others have said this using different words, but evolution relies on the preservation of low-cost mutations. It took many mutations to get from photoreceptors to the mammalian eyeball. If the cost is small enough that other factors dominate your ability to procreate, it will spread to all of your descendants. If other genes in your genome make you reproductively successful, that gene edit will spread and spread. It’s a good thing these cheap changes are preserved, or viruses and bacteria would have wiped out all multicellular life early on by practicing patience. We all have genes that make us less susceptible to some pathogens than others and if a bad enough variant comes around, suddenly we are over represented in the next generation. If the hits keep coming eventually our family reunion may be the only one being held.
elliekelly 5y ago
Can’t an inherited trait be “neutral”? By that I mean it confers neither a benefit nor a detriment? It’s my understanding that the baby toe, for example, isn’t particularly useful anymore. But having or not having the baby toe(s) isn’t likely to help or hinder a person’s ability to reach adulthood and reproduce. There must be a lot of traits like that, right? Like eye color or maybe wisdom teeth. No one (as far as I know) is selecting a sex partner based on whether their wisdom teeth were impacted or not.
jfrunyon 5y ago
That's not how selection works. If something doesn't decrease survivability, then there is no reason why evolution would get rid of it.
robbiep 5y ago
This is a profound misunderstanding of the driving forces of evolution. Why do we have wisdom teeth? Just because something is useless doesn’t mean it’s eliminated

323 5y ago

They are wrong. > The appendix has been identified as an important component of mammalian mucosal immune function, particularly B cell-mediated immune responses and extrathymically derived T cells. https://en.wikipedia.org/wiki/Appendix_(anatomy)#Functions https://en.wikipedia.org/wiki/Appendix_(anatomy)#Functions

neuronic 5y ago
Do we have data on COVID in people without appendix?