> 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
So does the Encyclopedia Brittanica, Healthline, and any number of other sources:
> appendix, formally vermiform appendix, in anatomy, a vestigial hollow tube
> 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.
It likely has some complex purpose, such as a reservoir for microbiome.
The same logic would apply to male nipples. It's a flawed logic.
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.
Many females also find male nipples attractive.
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).
And I don't think it's just giraffes, it's all mammals, which also points to a common ancestor.
https://bioone.org/journals/acta-palaeontologica-polonica/vo...
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.
Untreated appendicitis is quite deadly. I would say there is definitely some advantage.
Except that yes it is an argument against it.
Your reduction breaks down because it conflates "a reason" with "all reasons".
See: dementia, cancer.
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.
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.
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.
Which is what we see all the time in programming: software wins because of its effect, not usually the lines of code needed (or not) to get there.
If you remove noncoding "junk DNA", you alter the higher level spatial configuration of DNA. Histone winding changes which promoter regions are accessible, gene dosing is altered, binding affinity and kinetics change, etc. These are dynamical equations you're dramatically altering.
Non-coding DNA also likely shields against several classes of random point mutations, base substitutions, transposition, etc. preventing cancer and cell physiological disease states.
It's also important for maintaining alignment during crossover.
If it truly served no purpose, it would be gone.
> The idea that modern higher organisms have been "optimized" so that every part is essential
Essential is the wrong word here. Relying on every part for survival would put us at risk. We have plenty of built in redundancies to support degradation, failure, and loss of multiple systems and functions.
I get your argument, but I still disagree. At the species / population level, we have been optimized as wholesale organisms as best as development and body plans will allow. Everything not subject to pressure will get washed away.
Despite our vestigial tails, the coccyx supports our weight while we are seated. As I postulated before, the appendix probably has a net positive function in supporting gut microflora and our "junk DNA" plays a role at the molecular level.
Why? Removing it serves no purpose either.
I think I’m not going out on a limb to say that no modern evolutionary biologist believes organisms are optimal. They simply survived.
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.
Why do we have wisdom teeth? Just because something is useless doesn’t mean it’s eliminated
It's pretty much an on-site backup for intestinal flora :)