The sensory function of hairs: The Omission that made Darwin wrong about "nakedness".

Discussion in 'Biology & Genetics' started by Ken Fabian, Nov 20, 2023.

  1. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    You are conflating two things:
    1. the loss of most of our hair
    2. the evolution of what hair we have left, and why we didn't go entirely bald etc.
    You seem to be saying that because a theory to explain 1 isn't about the sensory function of hair that this means that they're arguing against the sensory function importance for 2. That isn't the case at all. They're not competing against each other, but theories for 1 and 2 can run in parallel. So please stop thinking that they're in competition.
    Pinball1970 and DaveC426913 like this.
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  3. Pinball1970 Valued Senior Member

    Darwin thought very deeply. He waited a very long time before publishing "Origins" and obviously he was wrong about things that took decades after his death to work out.
    Things have moved on in the same way we have moved on from from other scientists from the 19thC.
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  5. Ken Fabian Registered Member

    And you seem to be assuming ectoparasite avoidance - which sensory sensitivity would enhance - could/would have no role in the initial evolving of furlessness. And assuming incremental change rather than abrupt - that there was ongoing hair loss headed towards true hairlessness, that had to stop for the hairs to gain another role. I think you are assuming the order changes happened in.

    I've said already ectoparasite and thermoregulation hypotheses are not in competition. As well as possibly evolving in parallel (or independently) the different elements - hair size, follicle nerve supply, eccrine glands - can also evolve sequentially. Getting the hot weather endurance need not be the immediate benefit, but a benefit that emerged later with subsequent evolution of sweatiness and that reinforced the success of the furless hominid and prevented a reversion. As sensory sensitivity could have evolved later. I don't know, but neither does anyone else, not even biologists specialising in evolutionary anthropology. All possibilities deserve and arguably require consideration. Unless we can bypass the surmising and hypothesising and we end up being able to read our evolutionary history from our DNA.

    Given what anatomy tells us - that we have evolved exceptional sensory sensitivity - it seems like that matters, or else requires showing that it has no relevance to evolving furlessness. That has not been done.

    I don't know which order - no-one does - and we don't even know if the changes (or which aspects of hair size, follicle nerves, eccrine glands) could have been abrupt or which, if any might have or must have evolved incrementally. Abrupt mutational changes to developmental genetics could see spandrel-like combinations, including I would suppose, furlessness plus increased sweatiness or all of them together or combinations of them.

    Incremental evolution? Given what we see - a developmental trait that is primarily and universally expressed in the pre-pubescent young, who appear to be retaining infantile furlessness (small hairs not growing larger on time, not loss of hairs) until puberty - and that furless childhood is universal and shows no apparent differentiation across the entire species, no matter how varied the post-puberty, secondary sexual hairiness. We don't see evidence of incremental change to that development, just to post-puberty traits. And the assumption that loss of hair in humans remains ongoing - that we are becoming more hairless - is one more unsupported assumption that remains popular.

    Furlessness alone can give immediate benefits with respect to fur borne parasites and parasite borne disease - differences in disease susceptibility can be a powerful and fast natural selector, changing the balance of a population potentially within a single generation. It would work better with enhanced sensitivity but would not require it.

    But furlessness alone won't give thermoregulatory advantage - and appears to give significant thermoregulatory disadvantage for children. Not without the significant change to eccrine glands as well.

    The enduring absence of due consideration for a sensory function that enhances parasite detection is something I can't see as anything but scientific negligence, a failure of basic observation. And subsequent to Montagna's anatomical observations - 1985 onwards - a failure of basic academic research.

    Body hair in modern humans serves no useful purpose
    was the enduring assumption (that still persists), reinforced by persistent absence of recognising the very existence of the principle function human hairs demonstrably have. It is an assumption that is readily observable to be false.

    Darwin might have been capable of recognising hot weather endurance as an advantage of "nakedness" and therefore changed his view that furlessness could not have arisen from natural selection, but it was a failure of fundamental observation to not notice the sensory function of hair, which observation would also lead to the possibility that our furlessness evolved out of natural selection.
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  7. Ken Fabian Registered Member

    No, they haven't. That is at the heart of this discussion. I could even cite a paper published a century and more after Darwin where the ectoparasite hypothesis was dismissed simply because Darwin said.
  8. Pinball1970 Valued Senior Member

    If you can then that is poor science, we (Applied Biology UG) were taught the complete opposite of that. I.e. there are no authorities in science only experts, we were also taught that it was Gregor Mendel that worked out how genes were passed on and that Darwin was wrong on that.
    His guesses were pretty good on other things like where to find ancestors of Homo sapiens and obviously his work on natural selection and common ancestry stands up, although now the data is now huge and far more advanced with the advent of molecular biology and computer technology.
  9. Pinball1970 Valued Senior Member

    Btw a century after "Origin" is 1959, after his death is 1982 so 64 and 41 years ago respectively.
    Citing biology papers w.r.t. human physiology, genetics and evolution from over 40 years ago, has limitations.
    This would be like criticism of a cosmology paper w.r.t. DM pre Spitza, Chandra, HST or JWST.
  10. DaveC426913 Valued Senior Member

    I can't keep engaging this guy as long as his primary motive is dumping on Darwin and the entire anthro community. He's more interested in stroking his ego by "bravely standing up to the giants and their conspiracies".

    That's a pointless debate - theres no definitive answer to be had, but every word devoted to it - even from detractors - is just more time on his soapbox.

    I'll wait to see if he lets it go, and if he gets around to exploring any actual science behind his claim.
  11. Pinball1970 Valued Senior Member

    I had to get it in regarding how regarding the literature, if a student is researching the role of Methylation wrt to the Evolution and body hair, it does not make sense to go to when molecular biology was nascent or pre natal.
    Criticism of Darwin on points only illustrated decades after his death is pretty dumb.
  12. Ken Fabian Registered Member

    I don't see any engagement with the significance of enhanced sensory sensitivity or it's persistent omission from consideration. Or the significance of universal furlessness as a childhood trait that is homologous - universal within our species - and appears unaffected by any natural or sexual selection since (and likely carried from before) speciation. Or the significance for evolving thermoregulation of requiring two changes which, given eccrine glands are not part of the hair follicle package, so seem unlikely to appear together as part of change to hair follicles.

    Okay, people here seem to think the sensory function of hairs is of little or no consequence and if most biologists don't give it consideration it must not deserve any. People don't like my following that omission back through the literature on evolution of furlessness to Darwin and see criticising Darwin but aren't interested in the omission itself or how a false assumption - that human body hairs are effectively functionless and irrelevant - proliferated and persisted despite everyone except people with medical conditions living immersed in the sensations they make or how it continued to persist even after it was part of the literature. No-one has to engage of course and Dave doesn't have to engage at all.

    A repeat of a quote from my principle reference, William Montagna - (or is it just name-dropping?) -

    I'd like to see some engagement with the content of that, but I've stopped expecting any.
  13. DaveC426913 Valued Senior Member

    You are the one setting the direction of the thread. If you want people to engage with the science, you might consider dropping the discipline-blaming rhetoric.

    Please Register or Log in to view the hidden image!

    So why don't you clarify what (i.e. which), exactly, you want to discuss?
  14. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    So you're interested not in what Darwin said (per the OP) but rather simply on the evolution of the sensory sensitivity of what hair we have left? Is that correct?
    And I say you're not interested in what Darwin said that you quoted in your OP (reminder: "No one supposes that the nakedness of the skin is any direct advantage to man: his body, therefore, cannot have been divested of hair through natural selection.") because it is clear to most of us here that Darwin was referring in "divested of hair" is the change in man from fur to furless. I.e. the role of hair as we now have it is not part of what he was saying, rather just why we lost our fur. He seemed to be saying that he saw no evolutionary benefit in us losing our fur. This is a different matter to questioning how our remaining hair has evolved since that time, or why.

    So maybe that is why there hasn't been the focus you are looking for, because the OP is not framed for that discussion, and we're going by the OP.

    So, as DaveC suggests, and because I have undoubtedly misunderstood what it is you'd like to discuss, please can you clarify?
  15. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

    Yes, a transition to smaller hairs does not equate to them being otiose.

    Becoming less hirsute may have simply resulted from personal choices or social-group preferences in mates, as the Homo genus gradually acquired greater self-awareness and conceived the power to modify itself.

    IOW, some aspects of self-domestication would conform to aesthetic desires rather than practical, traditional evolutionary benefits. "Tameness" (whether self-selected or externally induced) can also lead to juvenile traits being retained in adult animals (human features have been compared to the physical characteristics of infant chimps).


    The most comprehensive case for human self-domestication has been proposed for the changes that account for the much later transition from robust humans such as Neanderthals or Denisovans to anatomically modern humans. Occurring between 40,000 and 25,000 years ago, this rapid neotenization has been explained as the result of cultural selection of mating partners on the basis of variables lacking evolutionary benefits, such as perceived attractiveness, facial symmetry, youth, specific body ratios, skin tone or hair, none of which play any role in any other animal species. This unintentional auto-domestication, coinciding with the introduction of imagery of female sexuality, occurred simultaneously in four continents then occupied by hominins. It led to rapid changes typical for domestication, such as in cranial morphology, skeletal architecture, reduction in brain volume, to playful and exploratory behavior, and the establishment of thousands of deleterious conditions, syndromes, disorders and illnesses presumed absent in robust humans.
  16. DaveC426913 Valued Senior Member

    An interesting hypothesis I hadn't considered.

    We still do that today, showing a cultural preference for younger and younger appearing traits.

    Even more intriguing!
    C C likes this.
  17. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

    Yah, there is that "curse side" to domestication and "aesthetic selection" that we've accumulated, similar to our pets and livestock.

    "We know certain features that appeal to people have serious impacts on health and happiness. For instance, flat-faced dogs struggle with breathing due to constricted nasal passages and shortened airways. This “air hunger” has been likened to experiencing an asthma attack. These dogs are also prone to higher rates of skin, eye and dental problems compared with dogs with longer muzzles.

    Many modern dogs depend on human medical intervention to reproduce. For instance, French Bulldogs and Chihuahuas frequently require a caesarean section to give birth, as the puppies’ heads are very large compared with the mother’s pelvic width. This reliance on surgery to breed highlights the profound impact intensive selective breeding has on dogs.
  18. DaveC426913 Valued Senior Member

    < sidebar >
    I am curious about the term self-domestication. It came up recently in regards to elephants, but it's even more cryptic when applied to humans.
    What does it mean?
    I get the self-selection part, but what is the applicability of the term 'domestication'?

    < ! -- Trying not to go too far off Ken's topic. -- >
    < /sidebar >
  19. C C Consular Corps - "the backbone of diplomacy" Valued Senior Member

    Did humans domesticate themselves?

    "One reason that made scientists claim that humans are self-domesticated lied within our behavior: modern humans are docile and tolerant, like domesticated species, our cooperative abilities and pro-social behaviour are key features of our modern cognition," says Cedric Boeckx.

    "The second reason is that modern humans, when compared to Neanderthals, present a more gracile phenotype that resembles the one seen in domesticates when compared to their wild-type cousins," added the expert.

    To identify signs of a self-domestication process in humans, researchers made a list of genes associated with domestication features in humans, out of the comparison with the genome in Neanderthals and Denisovans, extinct human species.

    Likewise, this will be it for me. There's always a thread that could be started devoted exclusively to exploring and evaluating the hypothesis.

    IMO (a doubting Thomas excerpt added at bottom), if they're going to shift to grounding and trying to justify the possibility in genetics, or that being what human self-domestication is going to rest on and be identified with in the future... Then it may be best to drop the term and shift to purely referencing the social level, where humans obviously do make some or many mating choices going against the grain of what evolution in traditional context might favor.

    Thus, why I threw in "aesthetic selection" as a tentative, alternative label. Maybe it was just the already built-in affection toward juvenile-like features that compelled those of the deep past to be attracted to an adult individual with finer hair, less aggressive behavior, a flatter face, or whatever characteristics.

    But with respect to any "far-out" mating choices, something more complicated could have been introduced by budding imaginations. By the time the brain became capable of proto-superstitious beliefs, who knows what odd cultural concoctions and habits might have been at work that are inaccessible for study.
    - - - - - - - - - - -

    Early humans domesticated themselves, new genetic evidence suggests

    "William Tecumseh Fitch III, an evolutionary biologist and cognitive scientist at the University of Vienna, says he is skeptical of "precise parallels" between human self-domestication and animal domestication. "These are processes with both similarities and differences," he says. "I also don't think mutations in one or a few genes will ever make a good model for the many, many genes involved in domestication.""
    Last edited: Dec 12, 2023
  20. Ken Fabian Registered Member

    I didn't think my opening post would be especially hard to understand, nor the posts after, which introduced some other aspects of evolution of furlessness I am interested in and raise questions for me. Some reasoned critique for why I am wrong would be as welcome as affirmation - I'd rather learn from my mistakes than be praised for them - but I am not seeing reasoned critique.

    OP - "If you don't know what hairs do for modern humans, how can it be possible to understand how and why they evolved that way?".

    Yes, academia can specifically make and keep the question how modern humans lost their fur (and has) and thereby specifically about the advantages of their absence whilst excluding how hairs/follicles in humans changed in other way but it seems like an unwarranted assumption to me that there is no relevance or interconnections.

    At the very least it has direct relevance to any ectoparasite hypotheses. And I think if Darwin had observed, considered and dismissed relevance of the sensory function of hairs he would have said so - so I think it is reasonable to think he was not treating the function of body hairs and loss of fur as different questions but was omitting consideration of them and treating the hairs as they are as effectively functionless. Our perceptions may blur the differences between sensations from hairs disturbed and skin contact but paying attention will show they are different. Just this morning I picked a walking paralysis tick off my dog and watched it crawl up my finger, without sensation... until it ran into some hairs and I could feel it's presence clearly. I expect our hominid ancestors relied much more on their senses and paid attention to them than we do.

    So I think the framing of the question itself as strictly about the loss of fur and not the function of the hairs follows on from failure to observe the significant function they have. I don't understand how saying that can be so controversial.

    I have provided links and quotes that show that "functionless" for what was left was taken as given - and, besides pointing out that basic body awareness shows otherwise, gave link and quotes for anatomical evidence of enhanced sensory sensitivity compared to other extant apes. And experimental evidence of that sensitivity to the presence of bedbugs compared to hairless skin. And links and quotes for "functionless" persisting as assumption after it became part of the literature. I don't see any way of reconciling "no function" with "Thus, every hair in human skin, even the very small ones, functions like a vibrissa. This fact emphasizes the high degree of sensory acuity in human skin;" So, yes, I am critical of the quality of scholarship around evolution of human furlessness, past and present.

    Thank you Sarkus for engaging civilly but if you can't understand what I've been talking about from what I've posted so far I don't expect more will change that.

    I am not going to keep going. I would welcome reasoned critique but I think this is not the forum for getting it.
  21. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

    That's okay. Your OP, or at least your quote regarding Darwin and commentary thereof, was irrelevant to the points you actually wanted to make. Maybe if you are clearer at the outset in what you want to discuss, people will discuss that rather than the irrelevant packing material you surround it with.

    As it is, I have no interest in that which you do want to discuss, alas. So I'll bid you good day on the matter.

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