5 ms·

The ancestors are not among us

41 points by Hooke 10y ago

trjordan 10y ago
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.
kazinator 10y ago
> I think this use of the term is related to the misconception that some living taxa are the ancestors of other living taxa. The misconception is that some living taxa are identical to some ancestral taxa from which something else has also descended that is different. But isn't it the case that some are at least close (for some intents and purposes)? Crudely, apes haven't gone away because there are humans. Bacteria are still here and so on. Just they are not exactly the same like bacteria 300 million years ago.
- nathandaly 10y ago
  I think this is exactly the distinction the article is trykng to make. The statement "apes haven't gone away because there are humans" has a false premise: apes have changed a whole bunch since the common ancestor they share with humans, just like humans have. Back when there were no humans as we know them, there were also no apes as we know them. As far as I remember from biology, even if there is no selection pressure on a population, the population will still experience genetic drift and will still change over time.
- Scarblac 10y ago
  > Crudely, apes haven't gone away because there are humans. Humans _are_ apes. That's how much apes have changed. Other currently existing species of ape have probably changed about as much from our common ancestor (who was also an ape).

41 points by Hooke 10y ago

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.

kazinator 10y ago

> I think this use of the term is related to the misconception that some living taxa are the ancestors of other living taxa. The misconception is that some living taxa are identical to some ancestral taxa from which something else has also descended that is different. But isn't it the case that some are at least close (for some intents and purposes)? Crudely, apes haven't gone away because there are humans. Bacteria are still here and so on. Just they are not exactly the same like bacteria 300 million years ago.

nathandaly 10y ago
I think this is exactly the distinction the article is trykng to make. The statement "apes haven't gone away because there are humans" has a false premise: apes have changed a whole bunch since the common ancestor they share with humans, just like humans have. Back when there were no humans as we know them, there were also no apes as we know them. As far as I remember from biology, even if there is no selection pressure on a population, the population will still experience genetic drift and will still change over time.
Scarblac 10y ago
> Crudely, apes haven't gone away because there are humans. Humans _are_ apes. That's how much apes have changed. Other currently existing species of ape have probably changed about as much from our common ancestor (who was also an ape).