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Trying to say they have heads at all seems like trying to cram a square peg into a round hole. It's interesting that their bodies evolved from what was once th

Trying to say they have heads at all seems like trying to cram a square peg into a round hole. It's interesting that their bodies evolved from what was once the head of their ancestors, but in what meaningful sense is it presently a head? It's more like "head" is a discrete label created by and for the convenience of humans, and being a discrete label it doesn't really map cleanly to real world data in all cases. It's like saying humans have four legs, or dogs have two arms, because the front/top two limbs are related to each other. The labels of 'legs' and 'arms' aren't really meant to be used in this way, regardless of what evolutionary history says.

radarsat1 3y ago
I agreed with you until I read the article. It actually makes some really interesting observations about the comparison it's making regarding the typical definition of "head" and how body parts in general relate to gene expression patterns. The images in the article are really cool.
- mcpackieh 3y ago
  The article convinced me that starfish bodies developed from heads, just as I'm convinced that primate arms developed from legs, but it didn't convince me that it's appropriate to call the modern forms of these things heads or legs.
  - svnt 3y ago
    If your education includes substantial aspects of evolutionary developmental biology and genetics, then you have important mental models with which you can work with an organism. If you discover that the whole organism is effectively developmentally a head, then it is extremely appropriate to refer to it essentially as a head. If you instead relate to the organism in its present form in some more mundane ways then it might not seem that way. Analogies are failing me, but perhaps it would be like realizing an entire government basically spawned out of the centering concept of religious freedom. The structure of it then makes a lot more sense.
    - nyanpasu64 3y ago
      I'd say that whale flippers are homologous to legs/feet, but aren't legs/feet. This article says that starfish are homologous to heads, but I'm not sure whether I'd consider their bodies to be heads or not.
      - svnt 3y ago
        This discovery is to our understanding of starfish what Georges Cuvier’s discoveries of vertebrate morphology were to your present understanding of whales.
  - twic 3y ago
    Words only have meanings in context. It might now be that in the context of developmental biology, starfish have heads. It is surely the case that in the context of millinery, they do not. But no particular context is canonical, and so you cannot say that in an absolute, context-independent sense starfish do or do not have heads.
  - Sharlin 3y ago
    For legs and their homologues we have the word "limb" (or should I say fins and their homologues? After all, cladistically we're all fish!) but there hasn't been a need for a term for "head and its homologues". At least not until now, I guess.
pohl 3y ago
The pointwise measurable signatures of genes expressing for head vs trunk kind of deflate that perspective a tad.
chimpanzee 3y ago
Arm yourselves! The head of the language police has arrived To butt his nose into your thoughts To tell you what is meant to be or not. This mouthy busybody rarely rhymes and always prefers others mime. Metaphors, just confusing bores. Similes, not much more. If Orwell had a Frankenstein, he might to us remind: “An elbow is L-bowed only some of the times!”
- kyleee 3y ago
  Would it really be correct to refer to this person as the “head” of the language police?
  - Nexxius 3y ago
    Only if he is in charge of thought crimes.
kylebenzle 3y ago
You are exactly right and wrong. I teach biology at OSU and tease my students by asking, "Do humans have gills?" Do we? What would you answer? Then, "Do humans have tails?" Do YOU have a tail? The answer to both, in biology and evolutionary, YES, we have both. In the case of echinoderms what they have now "used to be" a head, so they are a head.
- mcpackieh 3y ago
  > The answer to both, in biology and evolutionary, YES, we have both. But only in those limited contexts is it true, and even then there are caveats. For instance biology textbooks will tell you that great apes are tailless primates. And in virtually any practical sense that's true. You can't yank a gorilla or a human by the tail. You can't get your tail caught in door. Your pants don't have a hole for your tail to poke through. If you told a child that gorillas have tails, you would be seriously misleading that child even if in some technical sense it was true. You would have to explain that gorillas only have tails in a very specific technical sort of way. If you aren't trying to be cheeky and entertain students with counterintuitive claims, then you would say that great apes have coccyxes, e.g. tailbones, which are the remnants of lost tails. How about this: Are whales fish? In the traditional sense, a fish is an animal that lives in the water, so whales (and starfish) are plainly fish. But anybody who has ever heard from marine biologists will exclaim that whales certainly are not fish, they're marine mammals. People will be very annoyed with you if you ever call a whale a fish, they'll take it as an insult to whales. But all mammals, including whales, are tetrapods and descended from an ancient lobe-finned fish. So in a cladistic sense you can claim that whales are fish. In the same sense, humans are also fish. And why not? As you say, we have gills too!
  - kylebenzle 3y ago
    You are not correct about a lot of what you are saying. Whales are not fish, but birds are dinosaurs, and humans have gills and tails, but your made up version of "whales are fish" might sound superficially similar but its not how any of that works. You can not "claim whales are fish" but humans do have gills and those are not the same thing, you are just confusing the two examples because they sound the same.
TheBigSalad 3y ago
I belive they are only saying the beefy center of the starfish body evolved from a head with legs, rather than a body with 5 legs. It doesn't mean we have to label it a 'head', but that language helps people understand.
xg15 3y ago
I think the more amazing insight here (not a new one though) is that "head" and "torso" aren't just human categories, they are at the root of some very old genes that govern body development for a vast number of species. So starfishes are "heads without bodies" in the sense that they use the molecular/genetic mechanism that in other species shapes the creature's head, but use it here for the entire body.

radarsat1 3y ago

I agreed with you until I read the article. It actually makes some really interesting observations about the comparison it's making regarding the typical definition of "head" and how body parts in general relate to gene expression patterns. The images in the article are really cool.

mcpackieh 3y ago
The article convinced me that starfish bodies developed from heads, just as I'm convinced that primate arms developed from legs, but it didn't convince me that it's appropriate to call the modern forms of these things heads or legs.
- svnt 3y ago
  If your education includes substantial aspects of evolutionary developmental biology and genetics, then you have important mental models with which you can work with an organism. If you discover that the whole organism is effectively developmentally a head, then it is extremely appropriate to refer to it essentially as a head. If you instead relate to the organism in its present form in some more mundane ways then it might not seem that way. Analogies are failing me, but perhaps it would be like realizing an entire government basically spawned out of the centering concept of religious freedom. The structure of it then makes a lot more sense.
  - nyanpasu64 3y ago
    I'd say that whale flippers are homologous to legs/feet, but aren't legs/feet. This article says that starfish are homologous to heads, but I'm not sure whether I'd consider their bodies to be heads or not.
    - svnt 3y ago
      This discovery is to our understanding of starfish what Georges Cuvier’s discoveries of vertebrate morphology were to your present understanding of whales.
- twic 3y ago
  Words only have meanings in context. It might now be that in the context of developmental biology, starfish have heads. It is surely the case that in the context of millinery, they do not. But no particular context is canonical, and so you cannot say that in an absolute, context-independent sense starfish do or do not have heads.
- Sharlin 3y ago
  For legs and their homologues we have the word "limb" (or should I say fins and their homologues? After all, cladistically we're all fish!) but there hasn't been a need for a term for "head and its homologues". At least not until now, I guess.

pohl 3y ago

The pointwise measurable signatures of genes expressing for head vs trunk kind of deflate that perspective a tad.

chimpanzee 3y ago

Arm yourselves! The head of the language police has arrived To butt his nose into your thoughts To tell you what is meant to be or not. This mouthy busybody rarely rhymes and always prefers others mime. Metaphors, just confusing bores. Similes, not much more. If Orwell had a Frankenstein, he might to us remind: “An elbow is L-bowed only some of the times!”

kyleee 3y ago
Would it really be correct to refer to this person as the “head” of the language police?
- Nexxius 3y ago
  Only if he is in charge of thought crimes.

kylebenzle 3y ago

You are exactly right and wrong. I teach biology at OSU and tease my students by asking, "Do humans have gills?" Do we? What would you answer? Then, "Do humans have tails?" Do YOU have a tail? The answer to both, in biology and evolutionary, YES, we have both. In the case of echinoderms what they have now "used to be" a head, so they are a head.

mcpackieh 3y ago
> The answer to both, in biology and evolutionary, YES, we have both. But only in those limited contexts is it true, and even then there are caveats. For instance biology textbooks will tell you that great apes are tailless primates. And in virtually any practical sense that's true. You can't yank a gorilla or a human by the tail. You can't get your tail caught in door. Your pants don't have a hole for your tail to poke through. If you told a child that gorillas have tails, you would be seriously misleading that child even if in some technical sense it was true. You would have to explain that gorillas only have tails in a very specific technical sort of way. If you aren't trying to be cheeky and entertain students with counterintuitive claims, then you would say that great apes have coccyxes, e.g. tailbones, which are the remnants of lost tails. How about this: Are whales fish? In the traditional sense, a fish is an animal that lives in the water, so whales (and starfish) are plainly fish. But anybody who has ever heard from marine biologists will exclaim that whales certainly are not fish, they're marine mammals. People will be very annoyed with you if you ever call a whale a fish, they'll take it as an insult to whales. But all mammals, including whales, are tetrapods and descended from an ancient lobe-finned fish. So in a cladistic sense you can claim that whales are fish. In the same sense, humans are also fish. And why not? As you say, we have gills too!
- kylebenzle 3y ago
  You are not correct about a lot of what you are saying. Whales are not fish, but birds are dinosaurs, and humans have gills and tails, but your made up version of "whales are fish" might sound superficially similar but its not how any of that works. You can not "claim whales are fish" but humans do have gills and those are not the same thing, you are just confusing the two examples because they sound the same.

TheBigSalad 3y ago

I belive they are only saying the beefy center of the starfish body evolved from a head with legs, rather than a body with 5 legs. It doesn't mean we have to label it a 'head', but that language helps people understand.

xg15 3y ago

I think the more amazing insight here (not a new one though) is that "head" and "torso" aren't just human categories, they are at the root of some very old genes that govern body development for a vast number of species. So starfishes are "heads without bodies" in the sense that they use the molecular/genetic mechanism that in other species shapes the creature's head, but use it here for the entire body.