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OK, I get the argument. But is there no validity to the idea that a species has not meaningfully changed in many years? I've heard this idea that modern sharks

OK, I get the argument. But is there no validity to the idea that a species has not meaningfully changed in many years? I've heard this idea that modern sharks are closer (in physiology) than human to our common ancestor. If I want to think about the common ancestor, I should think about a shark, not a human. I get that modern sharks are different than ancient sharks, but doesn't the idea of "living fossil" help me understand how much another species has changed over some time period?

tejtm 10y ago
I suppose it boils down to what is implied by your meaningfully. Will guess gross morphology and adaptation to ecological niche. In a sense one could argue sharks are more highly evolved because they out competed (or were luckier than) our ancestors and were not forced to change. Humans gross physical differences from the common ancestor are clearly more recent and therefore less refined. What cannot be said is: that in the interim we (sharks/humans) have not evolved every bit as much as one another. Evolution is not anthrocentric.
thaumasiotes 10y ago
> doesn't the idea of "living fossil" help me understand how much another species has changed over some time period? No, it doesn't. First, you'd need a measurement of "change". Without that, the question "how much change has occurred?" is, obviously, totally meaningless. Once you supply a measurement of "change", you'll notice one of two things: (1) (if your definition was motivated by defending the concept of living fossils): You've hung on to the idea that "living fossils" have changed less than "modern species", but your definition of "change" serves no useful purposes. (2) (if your definition was motivated without reference to "living fossils"): "Living fossils" mysteriously seem to be no different than any other species.
- jessaustin 10y ago
  Here's a measurement of "change" that really doesn't seem to have such dastardly motivations: body mass. I.e., if a species is much larger than its ancestors, it has changed a bunch. If not, it hasn't. On which horn of your dilemma will you try to catch me?
  - thaumasiotes 10y ago
    The first. It's very easy to show species with similar body mass that anyone sane would characterize as being very different from each other. What analysis will benefit by treating all similarly-massed descendant species of some clade as equivalent to each other, while those with different mass are different?
    - jessaustin 10y ago
      No that doesn't work. The first horn was all about motivation, which you don't mention here. You can't change the dilemma now. You used a perfectly reasonable technique to avoid providing a definition yourself; it just didn't work this time.
      - thaumasiotes 10y ago
        What motivated your choice of body mass? Feel free to adjust my remarks to, second, "if your definition was motivated honestly"; and first, "otherwise". You're not winning any points by saying "ah, but my motivation of trying to show you up is, unlike 'defending the concept of a living fossil', a useful scientific purpose'. As I have already pointed out twice below my first comment, the point of the dilemma is to illustrate that no definition of evolutionary change from which it is possible to extract useful information can support the concept of "living fossils". Which particular motivation you want to use, other than learning something useful, doesn't really matter. From a more formal philosophical perspective, I see no real need to have my description of the dilemma be so careful as to explicitly mention a motivation that can't exist in the absence of my presentation of the dilemma. I am satisfied to have accurately described the world as it exists in the absence of my description of it. You'll note that you did in fact observe one of the two things I predicted.
        jessaustin 10y ago
        My mistake, I thought the carefully-constructed dilemma was an attempt to avoid begging the question. Now it seems you're perfectly content to make that mistake; never mind.
- deleted 10y ago
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- nerdponx 10y ago
  This is a bizarre argument to me. Economists, for instance, do not have an agreed-upon definition for the "money supply". Nevertheless, it is perfectly reasonable to operate as if such a definition existed, so long as the details of its definition or not important in the discussion. Similarly, this is in the same vein as writing pseudocode containing a function that has not yet been defined. The exact execution steps of the program are not defined, but you can still reason about its flow all the same. To say that we cann't determine whether a species has changed, because we don't have a meaningful way to measure species change, is fine. It does not follow, however, that species change is inherently unmeasurable, and that therefore we just can't talk about it at all.
  - thaumasiotes 10y ago
    > It does not follow, however, that species change is inherently unmeasurable, and that therefore we just can't talk about it at all. Sure, and I didn't say or imply that anywhere. I said that no matter how you conceptualize evolutionary change, the concept "living fossil" will be nonsense.

tejtm 10y ago

I suppose it boils down to what is implied by your meaningfully. Will guess gross morphology and adaptation to ecological niche. In a sense one could argue sharks are more highly evolved because they out competed (or were luckier than) our ancestors and were not forced to change. Humans gross physical differences from the common ancestor are clearly more recent and therefore less refined. What cannot be said is: that in the interim we (sharks/humans) have not evolved every bit as much as one another. Evolution is not anthrocentric.

thaumasiotes 10y ago

> doesn't the idea of "living fossil" help me understand how much another species has changed over some time period? No, it doesn't. First, you'd need a measurement of "change". Without that, the question "how much change has occurred?" is, obviously, totally meaningless. Once you supply a measurement of "change", you'll notice one of two things: (1) (if your definition was motivated by defending the concept of living fossils): You've hung on to the idea that "living fossils" have changed less than "modern species", but your definition of "change" serves no useful purposes. (2) (if your definition was motivated without reference to "living fossils"): "Living fossils" mysteriously seem to be no different than any other species.

jessaustin 10y ago
Here's a measurement of "change" that really doesn't seem to have such dastardly motivations: body mass. I.e., if a species is much larger than its ancestors, it has changed a bunch. If not, it hasn't. On which horn of your dilemma will you try to catch me?
- thaumasiotes 10y ago
  The first. It's very easy to show species with similar body mass that anyone sane would characterize as being very different from each other. What analysis will benefit by treating all similarly-massed descendant species of some clade as equivalent to each other, while those with different mass are different?
  - jessaustin 10y ago
    No that doesn't work. The first horn was all about motivation, which you don't mention here. You can't change the dilemma now. You used a perfectly reasonable technique to avoid providing a definition yourself; it just didn't work this time.
    - thaumasiotes 10y ago
      What motivated your choice of body mass? Feel free to adjust my remarks to, second, "if your definition was motivated honestly"; and first, "otherwise". You're not winning any points by saying "ah, but my motivation of trying to show you up is, unlike 'defending the concept of a living fossil', a useful scientific purpose'. As I have already pointed out twice below my first comment, the point of the dilemma is to illustrate that no definition of evolutionary change from which it is possible to extract useful information can support the concept of "living fossils". Which particular motivation you want to use, other than learning something useful, doesn't really matter. From a more formal philosophical perspective, I see no real need to have my description of the dilemma be so careful as to explicitly mention a motivation that can't exist in the absence of my presentation of the dilemma. I am satisfied to have accurately described the world as it exists in the absence of my description of it. You'll note that you did in fact observe one of the two things I predicted.
      - jessaustin 10y ago
        My mistake, I thought the carefully-constructed dilemma was an attempt to avoid begging the question. Now it seems you're perfectly content to make that mistake; never mind.
deleted 10y ago
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nerdponx 10y ago
This is a bizarre argument to me. Economists, for instance, do not have an agreed-upon definition for the "money supply". Nevertheless, it is perfectly reasonable to operate as if such a definition existed, so long as the details of its definition or not important in the discussion. Similarly, this is in the same vein as writing pseudocode containing a function that has not yet been defined. The exact execution steps of the program are not defined, but you can still reason about its flow all the same. To say that we cann't determine whether a species has changed, because we don't have a meaningful way to measure species change, is fine. It does not follow, however, that species change is inherently unmeasurable, and that therefore we just can't talk about it at all.
- thaumasiotes 10y ago
  > It does not follow, however, that species change is inherently unmeasurable, and that therefore we just can't talk about it at all. Sure, and I didn't say or imply that anywhere. I said that no matter how you conceptualize evolutionary change, the concept "living fossil" will be nonsense.