[HN Gopher] We're not going to run out of new anatomy anytime soon
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       We're not going to run out of new anatomy anytime soon
        
       Author : jfil
       Score  : 177 points
       Date   : 2024-09-12 02:35 UTC (3 days ago)
        
 (HTM) web link (svpow.com)
 (TXT) w3m dump (svpow.com)
        
       | jamesy0ung wrote:
       | Link seems to be broken, Firefox is displaying raw JSON when I
       | visit it.
        
         | jraby3 wrote:
         | It's working for me.
        
       | roca wrote:
       | The incredible complexity of anatomy is even more amazing
       | considering
       | 
       | * all the structures grow from a single cell
       | 
       | * somehow it's all encoded in DNA (only 6 billion bits in humans,
       | which has to also build cells and their ultracomplex machinery)
       | 
       | * this all had to evolve using only a very noisy objective
       | function
        
         | dotancohen wrote:
         | > only 6 billion bits in humans
         | 
         | That's under 1 GB - it might all fit on a standard compact
         | disc.
        
           | lostlogin wrote:
           | > compact disc
           | 
           | It's probably not far off being easier to read DNA than a CD.
           | And it's surely less frustrating.
        
         | semitones wrote:
         | I wonder if saying that "it's all encoded in DNA (which is only
         | 6 billion bits)" is accurate. Every time life (considering only
         | humans for now, to simplify) arises, in addition to the DNA
         | (the "code"), you also have the rest of the first cell (the
         | zygote), which already has an "expression" of that code (which
         | may contain additional information beyond what is already in
         | the code), + the entire environment of the mother (which
         | obviously provides additional information).
         | 
         | This makes me think that we need far more than just 6 billion
         | bits to actually encode the entire process of new life
         | formation (each instance always piggy-backs off the previous,
         | and always provides processes/information).
        
           | rolisz wrote:
           | Michael Levin has some awesome experiments where he screws
           | around with the bioelectric fields of planetaria and he gets
           | them to grow two heads and no tail, while being genetically
           | identical to a normal one.
        
             | elric wrote:
             | One of my old classmates' area of research is applying
             | electric stimuli to various types of cells. Apparently the
             | right amount at the right time can briefly allow foreign
             | material to pass through the cell wall unimpeded. The
             | complexity of a single cell is insane, that of a complex
             | organism is way beyond insane.
        
               | dennis_jeeves2 wrote:
               | I think you meant cell membrane rather than cell wall?
               | 
               | (There is a contrarian theory that says that the cell
               | membrane does not exist at all, look up Gilbert Ling. So
               | it's no surprise that things can move in and out of the
               | cell under certain conditions.)
        
             | inglor_cz wrote:
             | Planaria. (Yeah, I am a pedant sometimes.) Also, frogs,
             | tadpoles, axolotls. Truly a wonderful mind. I admire him,
             | not least for his ability to do really weird and important
             | science outside the usual "don't do anything extraordinary"
             | boundaries set by ossified grant committees.
        
               | Gooblebrai wrote:
               | I thank you. I was looking for planetaria and I was
               | confused
        
               | rolisz wrote:
               | _facepalm_ Thank you. That was not pedantic at all, I
               | made an early morning mistake.
        
             | dmd wrote:
             | And you keep them in the planetarium, right?
        
           | wolpoli wrote:
           | You are telling me that we do not have a way to clean build
           | human from DNA source. That's a real continuity risk.
        
             | heckelson wrote:
             | The battle for reproducible builds continues
        
               | Aerbil313 wrote:
               | We need purely functional nanomachinery to create every
               | embrionic molecule from element atoms, and a declarative
               | physical language to combine them in the right way to
               | create a zygote.
        
             | emptiestplace wrote:
             | What if, as human consciousness is an emergent property of
             | complexity, so too are humans and DNA itself? Could it be
             | that, just as consciousness arises from the intricate
             | networks within the brain, life and its fundamental
             | components--like DNA--emerge from an even deeper layer of
             | complexity in the universe, suggesting that our very
             | existence is a product of systems far beyond our current
             | understanding?
        
               | gcr wrote:
               | If true, alien first contact scenarios get a lot more
               | interesting.
               | 
               | Someone should write a short story about that.
        
             | bgun wrote:
             | We do, but it's messy and usually involves a few years of
             | courtship, followed by one to three decades of raising &
             | educating the resulting human to anything resembling a
             | useful model for comparison.
        
               | gcr wrote:
               | No, the claim is much stronger than that: that the zygote
               | itself encodes necessary information that isn't captured
               | in DNA. Put another way, long after humans are extinct,
               | the claim is that if aliens could download our DNA source
               | code somehow, they still wouldn't be able to build humans
               | without replicating the zygote's internal structures
               | exactly. We'd come out as super deformed or something.
               | 
               | The claim is biological, not sociological.
        
               | shepherdjerred wrote:
               | e.g. imagine being given some source code and being told
               | to compile/execute it but you're not given any hardware.
        
               | tsimionescu wrote:
               | Not only that, but you're not even given the compiler. If
               | all you have is the DNA (even if you had the
               | mitochondrial DNA too), you have source code for a
               | language no one knows with no compiler.
               | 
               | Or, more accurately, it's like having binary machine code
               | for an unknown ISA with no information about the CPU, and
               | no example CPU.
        
               | Thiez wrote:
               | Perhaps the first generation would be deformed but
               | second-gen (if they hypothetically get that far) should
               | be much closer. You still need the mitochondrial DNA as
               | well.
        
               | tsimionescu wrote:
               | Well, first of all, they wouldn't be able to build a
               | single functioning cell if all they had was DNA (and even
               | if they had mitochondrial DNA too). Most organelles
               | divide independently of the nucleus, and there is no
               | reason to think that DNA encodes anything about their
               | fundamental structure. Even if some changes in genes can
               | effect some changes in the organelles, that doesn't mean
               | that the genes specify every detail of the organelle.
               | 
               | Also, even if we accepted that DNA fully specifies how a
               | cell can create an identical copy of the cell that
               | contains it, that doesn't mean that it specifies how to
               | create a cell from scratch. The "instructions" in DNA
               | could very well depend critically on details of the
               | current cell. For example, the DNA could specify se thing
               | like "take 1% of the substance secreted in organelle A
               | and mix it with 90% water and 9% the substance secreted
               | by organelle B". This instruction is perfectly good for
               | specifying a copy of the current cell, and perfectly
               | useless if you don't have the original cell for which it
               | is meant.
               | 
               | This sort of thing could very well apply at the level of
               | the whole fetus. Details of the uterus and other parts of
               | the mother organism may well be critical parts of the
               | "program" described by the DNA. For example, it's easy to
               | imagine that the early fetus follows instructions like
               | "let this much fluid pass through the umbilical chord",
               | or "grow horizontally until you find this much pH
               | difference between the extremeties" or whatever other
               | instructions that are only useful in the context of an
               | existing functioning mother organism.
               | 
               | And even beyond the individual, you would have a big
               | problem recreating the species to allow for a second
               | generation to exist at all. In particular, even if you
               | had a whole living healthy female mammal, you would have
               | no information at all for how to create a male of the
               | species, so no way to create sperm cells, so no way to
               | perpetuate the species. So the DNA of a female mammal
               | doesn't contain information for how to make more of the
               | species. And if all you had was a male organism, you
               | would lack the information probably encoded in the living
               | female that I was discussing earlier.
               | 
               | As a side note, this problem would not exist for birds,
               | where the female bird does have both male and female DNA.
        
             | delecti wrote:
             | I mean, is that really true when the "we" is a group of 8
             | billion, about half of whom at any time can contribute to a
             | build server?
        
               | bregma wrote:
               | Mathematically it's true. Anything that can be enumerated
               | (that is, has an ontological mapping with the set of
               | whole numbers) can be interpreted as input to some
               | function which can be evaluated to some result also with
               | an ontological mapping with the set of whole numbers. In
               | other words, the entire human population could be a part
               | of some program calculating the answer to some universal
               | question, which may be about life, the universe, and
               | everything. In fact, the answer may already be known.
               | We're just one big server with massively parallel
               | operation.
               | 
               | What we don't know is what that function is. Put
               | differently, what is the question?
        
           | admissionsguy wrote:
           | > you also have the rest of the first cell (the zygote),
           | which already has an "expression" of that code
           | 
           | It's called maternal effect
           | (https://en.wikipedia.org/wiki/Maternal_effect)
        
             | tsimionescu wrote:
             | I think they meant something even more basic, and common to
             | all cells: you can't make a new cell without an existing
             | living functioning cell. We have no firm idea of how the
             | first cells developed, but all of the cells we know of
             | today come from the division of another cell, and we have
             | never observed anything remotely like a new cell forming
             | pit of a puddle of all the required substances and DNA.
        
           | moi2388 wrote:
           | You might want to look up Dr.Michael Levin.
           | 
           | He is studying exactly this. He found that when developing,
           | cells move and grow in a particular direction. But when an
           | obstacle is placed in their way, they move around it to
           | somehow still end up where they're supposed to.
           | 
           | DNA is not all of the encoding. Even cells appear to have
           | some form of navigation or space search capabilities.
        
             | fellowmartian wrote:
             | His work is mind-blowing and completely upturned my
             | perception of biology.
        
             | codesnik wrote:
             | chemical gradients?
        
             | doctorpangloss wrote:
             | Why do miscarriages occur? They are frequent, so they seem
             | to be an essential feature of pregnancy.
        
               | cultofmetatron wrote:
               | I imagine from an evolutionary perspective, a false
               | positive of the fetus bringing harm to the mother is
               | preferable over the long term for increasing long term
               | reproductive survival.
        
               | candiddevmike wrote:
               | The fetus's liveliness check failed
        
               | im3w1l wrote:
               | Miscarriages must occur because our DNA is constantly
               | mutating. Some of those mutations will be so harmful that
               | the new organism cannot even survive until birth.
               | 
               | In addition to those unavoidable ones, there can also be
               | things going wrong by accident (e.g. the pregnant woman
               | suffer physical injury which kills the fetus).
        
               | pas wrote:
               | lack of immune tolerance in the mother.
               | 
               | for example (pre)eclampsia. we still don't know WTF is
               | going on exactly (but it's basically abnormal blood
               | vessel formation between the fetus and the uterus), and a
               | few decades ago it was basically guaranteed loss of the
               | fetus or the mother (or both), in about half a percent of
               | pregnancies.
               | 
               | nowadays thanks to medical science it's a hundred-times
               | more manageable.
        
           | joshuahedlund wrote:
           | Yes, I recently read the book _The Master Builder_ by Alfonso
           | Arias which gets into some of the detailed pre-requisites
           | provided by existing cells. (it's also why restoring extinct
           | species may be harder than expected even knowing their full
           | genetic sequence)
        
           | thfuran wrote:
           | At the very least, epigenetics are also partially heritable.
        
           | dekhn wrote:
           | https://en.wikipedia.org/wiki/Maternal_effect The egg
           | contains mRNA or protein created by the mother that affects
           | the child's phentotype.
           | 
           | It's unclear how much those non-genomic components affect
           | organismal phenotypes; presumably, there is some minimal
           | collection of factors that would suffice to allow us to
           | construct an artificial egg cell that is viable for
           | reproduction.
        
           | TZubiri wrote:
           | Disclaimer. I'm not a great biologist.
           | 
           | Couldn't this be proven by growing mammals in petri dishes?
           | 
           | If the entire information is encoded in DNA, then the fetus
           | would grow fine.
           | 
           | If however, the fetus needs to be in a womb to develop, then
           | there must be information (and resources) that need to be
           | sent from the mother to the baby in a sort of quine fashion.
           | 
           | Consider a Java compiler or python interpreter, they are
           | themselves written in the target language, unless we are
           | talking about early version. So you already need a java
           | compiler to compile Java, the code for the compiler does not
           | hold all of the necessary information, as you need a mother
           | compiler to execute it.
           | 
           | Which part of the target is in the code and which in the
           | interpreter/compiler?
           | 
           | A thought experiment would be a language where a built in
           | statement compile() compiles code according to
           | specifications. Thus the code for a compiler would simply be
           | compile().
           | 
           | My best guess is that fetuses can only grow inside a
           | functioning human, and that the information in DNA is not
           | sufficient, you need a functioning specimen to grow another
           | specimen.
        
         | 9dev wrote:
         | I wonder if it's actually more similar to procedural
         | generation, based on a seed value, that reliably recreates the
         | same complex output that isn't entirely described by the seed
         | alone. In this case, the DNA would just serve as input to a
         | myriad of algorithms that yield a fully working cell. A single
         | base pair change may lead to a mind-bogglingly long chain of
         | side effects that result in a third arm, or really just nothing
         | at all.
        
         | tialaramex wrote:
         | > only 6 billion bits in humans
         | 
         | A 27-state two value Busy Beaver can implement "Give a counter-
         | example to Goldbach's Conjecture" - if there are none the
         | program never halts. We can recognise that, and say "Oh dear"
         | but it gets us no closer to an answer. Six billion isn't even
         | in the right ballpark, our ability to understand the meaning of
         | every self-acting machine extends maybe to six or seven bits if
         | we're very smart.
        
         | refurb wrote:
         | > somehow it's all encoded in DNA (only 6 billion bits in
         | humans, which has to also build cells and their ultracomplex
         | machinery)
         | 
         | One has to be cautious to not assume that the only data DNA
         | holds is in base pairs.
         | 
         | We know that secondary factors like inter- and intra-strand
         | interactions or DNA-histone interaction encodes information as
         | well.
         | 
         | A good analogy is a book. While it is made up of individual
         | letters, the combinations build to words, which build to
         | sentences, which build to ideas, which can interact with other
         | ideas (sometimes in other chapters!) to create a complexity
         | beyond just the combination of letters would suggest.
         | 
         | That's not even getting into the temporal aspects of DNA
         | expression.
        
           | candiddevmike wrote:
           | I believe DNA is a compression algorithm beyond our current
           | understanding, and the 6 billion bits is a post-compression
           | size.
        
         | thih9 wrote:
         | > 6 billion bits in humans
         | 
         | ~750 megabytes (unit conversion via google)
        
         | BurningFrog wrote:
         | > _all the structures grow from a single cell_
         | 
         | Two cells: Egg and sperm
        
           | yjftsjthsd-h wrote:
           | ...which merge into a single zygote cell.
        
           | Metacelsus wrote:
           | A fertilized egg (zygote) is one cell.
        
         | lubujackson wrote:
         | A crappy, self-improving function with a decent feedback loop
         | (survival) can get pretty far given 100s of millions of years
         | with hundreds of million (or trillions) of concurrent
         | experiments running at the same time. The time scale of life is
         | the hardest element to comprehend.
        
         | wonnage wrote:
         | I don't think it's true that DNA actually encodes an entire
         | organism. Leaving all discussion of epigenetics aside, the
         | proteins produced from DNA can basically do anything, including
         | modifying DNA. Maybe we could think of large portions of DNA as
         | simply bindings to shared libraries (i.e, the proteins). Or
         | like a package manifest and build script for life rather than
         | the code itself
        
       | MattGaiser wrote:
       | If I understand his three groups correctly, he's basically saying
       | that one of the big bottlenecks is that nobody is looking full
       | time.
       | 
       | Basically, nobody has the job of discovering human anatomy except
       | as a side hustle or byproduct.
       | 
       | I'm quite surprised at that. That's a remarkable area to not have
       | full time researchers in.
        
         | Validark wrote:
         | It's sad to think about how little of our resources are
         | dedicated to work like this. Although I enjoyed the Marvel
         | movies growing up, it would be nice if similar funding could be
         | found for a project like the author describes (and, of course,
         | you could have a sort of documentary showing people what they
         | discovered).
        
         | amelius wrote:
         | I think he missed at least one group: pathologists.
        
         | twic wrote:
         | Is it? How would anyone make money or fame out of it?
         | 
         | The way our scientific establishment works now is that you are
         | rewarded for discovering things which fit into and shed new
         | light on our existing web of understanding, not for things
         | which are completely new and unconnected. I don't think this is
         | entirely bad - science is useful because it's a densely
         | connected web rather than a bag of unrelated facts. But it does
         | mean that very little value is attached to observations of
         | weird new things that don't fit in anywhere.
         | 
         | Back when I was a scientist, I was studying a known structure
         | in the cytoskeleton. By chance, some of the cells I prepared
         | went funny, and produced a radically different structure that I
         | hadn't seen before, and couldn't find any mention of in the
         | literature. I showed my supervisor, who basically said "so
         | what?". On their own, this new structure was useless to a
         | career scientist, because you can't say anything about what it
         | is, what it does, why it's important, or how it connects to
         | what anyone else is publishing about.
         | 
         | (It turned out this structure had been seen before, and
         | published a few times, but still, nobody really knows what it's
         | all about)
        
       | elric wrote:
       | That was a super interesting read. Another factor that's probably
       | missing is a weird form of prudeness/sexism. I remember reading
       | articles years ago about new discoveries about the clitoris, and
       | thinkig "how the fuck was this missed", or the debate around the
       | existance of the G-spot, or the existence (or not) of female
       | ejaculate. I suspect there's more female anatomy left to be
       | discovered/described than male.
        
         | FrustratedMonky wrote:
         | I also think it is great to call out that not all 'missing'
         | things like this are a conspiracy, it is just inefficiencies,
         | or competing goals of different groups.
         | 
         | "No shadowy Illuminati group deliberately made this decision,
         | but as a civilization we have collectively 'decided' that three
         | groups of people would get to peer inside the human body, and
         | they'd all be hobbled."
        
           | elric wrote:
           | Oh indeed, I don't think there's a shadowy cabal suppressing
           | the knowledge of the existence of our third eye or anything
           | like that. But in the past, the long arm of the catholic
           | church certainly had a chilling effect on some research.
           | 
           | Like the guy who built some of the first microscopes and
           | discovered the sperm in semen, he wrote to the scientific
           | community to discuss the discovery, but made sure to include
           | that the semen he used was "what was left" after he copulated
           | with his wife. Wouldn't want to give anyone the idea that he
           | had masturbated, heaven forfend!
        
         | valval wrote:
         | You're looking at this from a point of view with inherent bias,
         | that has no guarantee of being lesser in degree than the ones
         | that produced the literature.
        
           | chowells wrote:
           | You're looking at this from the point of view that bias is
           | inherently bad. It's not. Biases do not need to be "lesser in
           | degree" to allow adding something new to a conversation. They
           | only need to be _different_ from existing ones.
           | 
           | You know, diversity improves results.
        
           | elric wrote:
           | Hmm, I spent some time thinking about this comment, and I
           | still don't get your point. Does my bias invalidate my claim?
           | I mean I don't have any hard evidence that this is happening,
           | but from a historical point is makes sense to me. If you
           | disagree, it would be helpful to point out why, rather than
           | to call out my bias.
        
         | nntwozz wrote:
         | The appendix also comes to mind, being told it was useless for
         | so long and now evidence suggests it has important functions
         | for the immune system.
        
         | hiisukun wrote:
         | In addition to the appendix, my go to example of this is my
         | friend's favourite organ: the Thymus [1]! If you've heard of
         | "T-Cells" you indirectly know about it.
         | 
         | The interesting thing is that it is in a human when they are
         | born, grows until puberty, then gets smaller and smaller until
         | it can be quite small and difficult to detect in a grown adult.
         | 
         | I can imagine medical explorers cutting open dead 40 year olds
         | in the year 1900, probably not finding any obvious organ there
         | -- while perhaps cutting open dead children may have been a lot
         | less common (and perhaps distasteful). If you did find
         | something there, you would not assume an important organ
         | present in a child and essential for their immune system would
         | shrink and almost go away.
         | 
         | It would be more likely to be labelled nothing, an abnormal
         | growth, or even a cause for death or illness (pressure on the
         | heart/lungs!).
        
           | bregma wrote:
           | I dunno. Comparative anatomy was a thing then and the
           | anatomist may even have been fond of sweetbreads. They were
           | still popular on menus in Paris when I was there a few months
           | ago. It's possible they were more notable for their absence
           | in adult humans.
        
           | dennis_jeeves2 wrote:
           | >my friend's favourite organ
           | 
           | Woody Allen's second favorite organ is the brain :
           | https://www.youtube.com/watch?v=ngizj5FIcjo
        
           | twic wrote:
           | Although, as it happens, the thymus was known at least as far
           | back as the ancient Greeks:
           | 
           | https://pubmed.ncbi.nlm.nih.gov/29858845/
        
           | dekhn wrote:
           | The thymus is amazing... I ignored it for a long time then
           | saw an amazing seminar. The thymus plays an important role in
           | training the immune system: it expresses cells similar to
           | cells all over the body, and then "educates" T-cells to avoid
           | attacking those. Failures of the thymus often lead to
           | autoimmune disorders.
        
         | jac241 wrote:
         | Maybe, but I think more likely is the time factor for med
         | students. There's really only time to find the major structures
         | implicated in disease. Surgeons also not likely dissecting
         | around the clitoris much. Wouldn't want to risk injury
         | obviously.
        
       | keepamovin wrote:
       | The author says that no one's gonna fund such work, but I really
       | think the stated multibillionaires should fund it.
       | 
       | biological anatomy makes it pretty clear that biological bodies
       | are complex layering of biopolymer sheets that perform incredible
       | mechanical, biochemical and other subtle energetic processes.
       | 
       | We could learn a lot about the robots we hope to build by
       | intricate studies of how Animal anatomy has really perfected the
       | art of efficient and compact mechanical motion and advanced
       | functions.
       | 
       | In a sense, the sophistication of the dense layering is akin to
       | how modern processor architectures, motherboard and fully
       | integrated circuits SOCs inside compact devices are kind of
       | composite materials of fused layers of nevertheless separate
       | components.
       | 
       | I believe this kind of work really should be funded.
        
       | verisimi wrote:
       | This is a great case study in how all science is hobbled.
       | 
       | Define categories, silo information - who will ever recognise
       | something unusual under their very nose?
        
       | 11235813213455 wrote:
       | I think human species real advantage is human hands, they are so
       | precise, for me that's what made the difference
        
         | atombender wrote:
         | I'm not sure what you mean by this comment. Was there a time
         | when you didn't have hands?
        
           | 11235813213455 wrote:
           | yes, when we were still bacterias or a bit later, even
           | monkeys hands are not always super precise
        
         | inglor_cz wrote:
         | I sometimes wonder if crows would be able to build a
         | civilization if they had human hands.
         | 
         | They may be about as smart as australopithecus, so there could
         | be an evolutionary feedback loop: tools-brain-better tools-
         | better brain.
         | 
         | But you can only do so much with a beak.
        
           | hinkley wrote:
           | In the Uplift books dolphins are given prosthetic arms.
           | That's already half future tech and you'd have to miniaturize
           | them for crows. No way to control them yet, in either case.
        
           | out_of_protocol wrote:
           | Crow's brains are very good at what they do because their
           | version of human's neocortex is in the center of the brain.
           | And this is the reason why crow's brains can't scale up,
           | there no enough space to grow "thinking" part of brain
        
         | fooker wrote:
         | Human hands are marvelously complicated, we don't appreciate
         | that much as we see our hands everyday.
         | 
         | Interestingly, a stark reminder for this came when image
         | generating models could generate everything except realistic
         | hands.
        
           | everybodyknows wrote:
           | Hands are notoriously difficult for human artists to draw as
           | well; this is perhaps one reason so few make the attempt
           | nowadays.
        
         | FredPret wrote:
         | And living above ground. Whales and octopuses might be geniuses
         | but they'll never have a tech tree because they can't melt
         | metal
        
       | dwighttk wrote:
       | Ant that's just the structures, next is the purpose
        
       | dannyxertify wrote:
       | There is still too many things to be discovered and hope AI will
       | give us a full understanding of it
        
       | btrettel wrote:
       | I just skimmed the article, but it reminds me of something from
       | my own PhD in fluid dynamics. I worked in liquid jets/sprays,
       | basically, when a stream of liquid flows from a nozzle and breaks
       | into droplets. Nearly everyone has seen this in some form.
       | 
       | I published a "regime diagram" improving the existing
       | categorization of types of liquid jet breakup. There were a lot
       | of changes from the status quo, but one that strikes me as
       | particularly sad was the addition of a new regime that I called
       | "turbulent Rayleigh". Every time men pee, they create a turbulent
       | Rayleigh liquid jet. Yet this was a mostly foreign concept to
       | spray researchers! You can find a few papers that identify what
       | they view as an anomaly, but the papers seem to be mostly ignored
       | and they don't go beyond saying something like "Something here is
       | weird, future researchers should look into this". I did my share,
       | making a theoretical model of the regime, showing how it's
       | fundamentally different from the conventional _laminar_ Rayleigh
       | regime. Most spray researchers would consider a  "Rayleigh" jet
       | to be inherently laminar, but that's a misconception.
       | 
       | The reason why this happened is that liquid jet/sprays research
       | is heavily biased towards fuel sprays, which rarely ever have
       | this regime. You basically need a long tube (or something
       | similar) to reduce the Reynolds number for turbulence to appear,
       | which usually doesn't happen in fuel spray nozzles. Fuel sprays
       | tend to have lower surface tension and higher viscosity than
       | water/pee too, which makes seeing a turbulent Rayleigh jet even
       | harder.
        
         | CoastalCoder wrote:
         | Ok, honest question:
         | 
         | Is this why guys have so much trouble peeing only into the
         | toilet bowl when standing?
        
           | btrettel wrote:
           | That's a problem of aim, not spray formation, and thus beyond
           | my expertise. The Rayleigh regimes produce large droplets
           | (mainly diameters similar to the orifice) and not a finer
           | spray that could go everywhere.
           | 
           | Also: Peeing into only the bowl won't necessarily minimize
           | the mess. Air gets "entrained" into the water and that
           | creates splatter. Best practice is to target the porcelain
           | inside the bowl (just above the water line) and adjust the
           | distance so that the stream has broken up less as droplets
           | will create more splatter than a solid stream.
        
             | saagarjha wrote:
             | You could also sit down.
        
           | Unbefleckt wrote:
           | I'm genuinely curious as to why this is, as someone who has
           | never had trouble aiming or covered the seat in piss.
        
           | mandmandam wrote:
           | There are different reasons for this.
           | 
           | The biggest one is that many guys are just vile. Sad but
           | true. They don't even _try_ to aim, because someone else will
           | clean it; and they don 't even wash their hands after.
           | 
           | The next biggest is that sometimes where you point isn't
           | where the stream goes, whether from a random pinch in the
           | tube or a proprioception error.
           | 
           | And sometimes the stream is split, and it's not entirely
           | predictable when that will happen.
           | 
           | Spray?? Never had an issue like that. Can't speak for
           | everyone though.
        
       | tgbugs wrote:
       | As part of an NIH consortium I work with two teams that are
       | collecting multi-scale anatomical data on the human vagus nerve
       | with one of the objectives being to start to get a handle on the
       | variability between individuals. The variability that the
       | experimental teams are seeing is beyond anything I expected,
       | though admittedly my assumptions were naive. The branching
       | structure and routing of the nerves is basically unique per human
       | and we are in the processes of determining whether there are
       | invariant rules (e.g. for branch ordering) that apply across all
       | individuals. And that is at the level of gross anatomy. So we
       | aren't even done with gross anatomy, despite many biologists
       | thinking that the foundations are complete and have been since
       | the 16th century. Turns out that if you want to be able to apply
       | our knowledge of gross anatomy for more complex clinical use
       | cases we need significantly more data about basic variability in
       | structure so that we know what additional data we need to collect
       | for each individual.
        
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