Five vestigial organs and functions (appendix not included)

New Scientist offers a list of the human body's five organs and functions that seem to be pretty much useless. (The appendix isn't on the list because recent research suggest it may actually be a "safe house" for helpful bacteria.) Making New Scientist's, er, cut of vestigial organs and functions are: vomeronasal organ, goose bumps, Darwin's point, tail bone, and wisdom teeth. From New Scientist:
Goose bumps
Though goose bumps are a reflex rather than a permanent anatomical structure, they are widely considered to be vestigial in humans. The pilomotor reflex, to give them one of their technical names, occurs when the tiny muscle at the base of a hair follicle contracts, pulling the hair upright. In birds or mammals with feathers, fur or spines, this creates a layer of insulating warm air in a cold snap, or a reason for a predator to think twice before attacking. But human hair is so puny that it is incapable of either of these functions.

Goose bumps in humans may, however, have taken on a minor new role. Like flushing, another thermoregulatory mechanism, they have become linked with emotional responses - notably fear, rage or the pleasure, say, of listening to beautiful music. This could serve as a signal to others. It may also heighten emotional reactions: there is some evidence, for instance, that a music-induced frisson causes changes of activity in the brain that are associated with pleasure.
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  1. I take no pleasure in being crude, but if I don’t stop spending all my time on internet message boards, I might as well add a certain other organ to the vestigial list.

  2. The Canadian TV series ReGenesis has a continuing plot point about the vomeronasal organ (called the Jacobson’s Organ in the series). One of the regular characters can smell emotions due to a side-effect of some gene therapy. In fact, it’s turning out to be the main long-arc plot of season 4.

  3. Hah take that anatomically correct humans, I don’t have a proper Darwin’s Point, my helix is actually folded flat against my ear. :)

  4. I don’t like this whole “That organ has the following FUNCTION” talk. Way too teleological (implying design, where there is none). I think you’re omitting a lot when you say “That organ has the following function” as opposed to “That organ, which is pretty much the result of a series of genetic accidents, was preserved because they happen to create the following EVOLUTIONARY ADVANTAGE”. The really interesting question is not what this or that structure does, but how this or that structure happened to do useful things at different stages of becoming what they are today.

    Don’t let me get started on the bacterial flagellum… (1, 2, 3, 4)

  5. @Airshowfan, I see your point but disagree that “function” necessarily implies design.

  6. There’s no question that the human appendix is a vestigial cecum (a digestive organ found in many other mammals). The fact that it may confer some advantage today to humans doesn’t deny the fact that it is still vestigial.

  7. We say they are vestigial because we can’t see the whole picture.

    Same way we think things happen by chance or at random. They do not. We just have no ability or inclination to observe in enough detail the why or the how.

    Is the dew claw (read: thumb) of a cat vestigial? Probably useless to the cat, but maybe not so useless if you think of the cat [etc.] as a carrier of genetic traits that some future species will use.

  8. We may not be able “to see the whole picture”, but

    1) We are able to see if homologous structures are performing analogously in different organisms.

    2) We can infer the ancestral state of structures.

    When a structure is no longer performing the ancestral “function” (to speak clearly although not in a teleological manner) we call it “vestigial”. That’s not the same thing as calling it “useless”. Appendices and dew claws may still confer some advantage to humans and cats respectively — that’s beside the point that as cecums and digits they are vestigial.

  9. #8: Is that the functional definition of “vestigial”? But a lot of features started with one “function” before adapting to a different one later down the evolutionary line, like Airshowfan’s flagellum links. If our fur was originally used to make us more aerodynamic underwater (I dunno if it’s true, just the first example I could think of), would it be considered “vestigal” even if it still performs the function of keeping us warm now?

  10. I warn you, don’t go reading the comments section in that New Scientist article. Nothing like creationism to ruin my day. Serenity now.

  11. Some bodyworkers, e.g. those focussing on CSF rhythm and pelvic floor stability, say the coccyx has important function, though in most people it’s stuck in place, slowly causing problems. Pottenger Foundation documented malnutrition over generations causing jaws to shrink, thus wisdom teeth needing to be removed in some.

  12. GD23, you realize that that’s like telling me “Don’t look down”, right? ;)

  13. I didn’t know that up to 35% of people don’t have wisdom teeth. I always thought it was smaller because I never heard of anyone else like me who didn’t have them. I kept waiting during my late teens and 20’s and even into my late 20’s for that painful eruption but it never came… and I thought, okay I’m a freak, but at least I didn’t get any pain from it, now I find out I’m in a minority but hardly unique. Weird.

  14. About wisdom teeth, how can they say

    “Not only are impacted wisdom teeth becoming more common, perhaps as many as 35% of people have no wisdom teeth at all, suggesting that we may be on an evolutionary trajectory to losing them altogether.”

    The only think that would make wisdom teeth statistically less likely in births would be differential reproductive success based on having or not having them, like if they commonly got infected and killed people. Or, I suppose gave them bad breath and kept them from getting laid. Have I been missing an epidemic of deaths from tooth decay?

  15. “Have I been missing an epidemic of deaths from tooth decay?”

    Possibly.
    I’ve read that flossing reduces ones risk of death from heart attack, which helped to motivate me to do it every day.

  16. Wow, I had no idea “Darwin’s Point” was called that, or was found on so few people. I draw a bit and I was putting it on every ear I drew. I guess I should stop that then. Huh.

  17. Organs have function because they are a result of design. Natural selection IS a form of design. It’s not intelligent, but it’s not random or accidental by any means.

  18. In the comment flash on the side, Scarybug, I briefly was terrified that I was going to go tumbling into the depths of creationist / darwinist debate again.

  19. The only think that would make wisdom teeth statistically less likely in births would be differential reproductive success based on having or not having them, like if they commonly got infected and killed people.

    I’m not an expert, but it seems that if it doesn’t confer a reproductive advantage a random mutation is more likely than not to eventually “break” the system and cause it to malfunction, and most likely to disable it. Sort of like how a lot of cave organisms lose their pigmentation after a number of generations, even though it’s not evolutionarily (?) advantageous to be white versus their original pigmentation. Because wisdom teeth suck.

  20. There’s been some research recently talking about the advantage of *not* having advanced adaptations. I think it was in NYT. For instance, animals with less intelligence live longer b/c they aren’t spending as many resources on big brains. Likewise, it may take more resources to put color in skin than leave it white (I don’t know this, just speculation), so it actually could be advantageous.

  21. @22 – Australia has the highest incidence of skin cancer in the world due to the emigration of fair-skinned Europeans. The cost of a little melanin would be far outweighed by the protective benefit in such sunny climes.

  22. @23 – Yeah, I was referring specifically to creatures that evolved in caves adapting to have white skin. But this applies too – my question would be whether the European ancestors of fair-skinned Australians evolved light skin as an advantage (i.e. takes more resources for more melanin) or whether the amount of pigmentation is resource-neutral.
    Distinction between advantage or simply not-a-disadvantage.

  23. having fair skin is advantageous in regions with low light levels, since it is thereby easier to synthesise vitamin D from sunlight. in regions with more solar exposure the melanin protection layer provides protection and vitamin D synthesis levels are still able to be sustained.

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