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I do appreciate this and I hope you don't perceive it as "arguing." My biological education is a little sketchy. Turning it around a little: if some members of

I do appreciate this and I hope you don't perceive it as "arguing." My biological education is a little sketchy. Turning it around a little: if some members of a mainland species move to an island and eventually become incapable of interbreeding with the original species, then it is always a new species. True or false? So "no-interbreeding" is sufficient but not necessary?

thaumasiotes 2y ago
> Turning it around a little: if some members of a mainland species move to an island and eventually become incapable of interbreeding with the original species, then it is always a new species. True or false? I think people would basically agree with this; true enough. > So "no-interbreeding" is sufficient but not necessary? Not quite; the example of bacteria, above, disproves the sufficiency of "no-interbreeding". (Bacteria do mix their genetic material, but they directly exchange it with each other, and then their children are clones of themselves. Imagine if, whenever you had sex, your partner took on some of your traits, and you took on some of theirs. This would obviate the need for your children to draw their traits from more than one parent, and that's how bacteria work.) There are asexual higher organisms, like some lizards, and they follow the taxonomic example of bacteria in that when two of them are genetically similar enough, we call them the same species despite the fact that - since they can't breed at all - they cannot interbreed. The fossil example is also incompatible with "no-interbreeding" being a sufficient criterion, though this is a bit less clear than the bacteria example; we can't determine whether two fossils were or weren't able to interbreed. We can be nearly certain that there is some pair of structurally similar-looking fossils out there that we have labeled as belonging to a single species, despite the fact that the individual organisms wouldn't have been able to breed with each other. You could make the argument that this is simply a mistake on our part, and that would have a lot of validity, but even viewed that way it's a mistake that cannot even theoretically be corrected, which causes some conceptual difficulties. The reason there are so many species concept is that species are just a reflection of the idea that two organisms are "the same". What it means to be "the same" varies in different contexts, according to, without claiming to be exhaustive, (1) what you care about; (2) what is possible in the space you're discussing [pigs can't do the direct genetic exchange that bacteria can]; and (3) what it's possible for you to know. > I do appreciate this and I hope you don't perceive it as "arguing." Don't worry about offending me; you seem to be in perfectly good faith so far.
- AlbertCory 2y ago
  ok. If we know that a species (1) is sexual, and (2) cannot interbreed with an individual of a superficially similar species, then it IS sufficient to say we have two species there. I think I have all the qualifiers :) Incidentally, today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp." I pointed out that by that standard, we're also 60% the same as a banana.
  - thaumasiotes 2y ago
    You might be interested in the concept of "ring species", which doesn't contradict the principle you just stated, but does conflict with the biological species concept. A ring species is a continuum of interbreeding populations such that the ends of the continuum are not interfertile. https://en.wikipedia.org/wiki/Ring_species https://en.wikipedia.org/wiki/Ring_species This parallels the phenomenon you see in languages where, for example, any two adjacent villages across a considerable distance will be able to speak to each other, even though villages at opposite ends of the continuum cannot do so. (The "ring" part of the term refers to the two ends of the interfertility continuum being located in the same geographic area, which is a red herring.) As the wikipedia page notes, the problem that this concept exposes is that interfertility is not a transitive relation, and therefore can't be an equivalence relation. > today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp." > I pointed out that by that standard, we're also 60% the same as a banana. The major problem here is that "to what degree is a person 'the same' as a chimp?" is not a well-defined question. Again, you would need to define what it means to be the same, and it will vary with what you care about. There are important ways in which we are the same as a banana; most obviously, you can eat a banana and expect to be nourished. This is not a given for an alien organism, even one that appears to be largely chemically identical to a banana. Whether the similarities reach 60% depends on how you convert them to numbers. We can note that the concept of 'species' assures us that any two humans are 100% "the same", as compared to a banana, whereas if you research relatedness the convention is that two brothers are 50% "the same" and two strangers are 0% "the same" (and bananas, not being human, don't exist), and if you're doing theology the convention is generally that even identical twins are 0% "the same". Summing that up, if you're told that two things are the same, the response is "the same how?" The reason the Facebook argument is stupid is that total shared DNA count isn't a useful thing to measure for most purposes. The salience of a difference in phenotype isn't closely related to the amount of DNA that changed to enable it.

thaumasiotes 2y ago

> Turning it around a little: if some members of a mainland species move to an island and eventually become incapable of interbreeding with the original species, then it is always a new species. True or false? I think people would basically agree with this; true enough. > So "no-interbreeding" is sufficient but not necessary? Not quite; the example of bacteria, above, disproves the sufficiency of "no-interbreeding". (Bacteria do mix their genetic material, but they directly exchange it with each other, and then their children are clones of themselves. Imagine if, whenever you had sex, your partner took on some of your traits, and you took on some of theirs. This would obviate the need for your children to draw their traits from more than one parent, and that's how bacteria work.) There are asexual higher organisms, like some lizards, and they follow the taxonomic example of bacteria in that when two of them are genetically similar enough, we call them the same species despite the fact that - since they can't breed at all - they cannot interbreed. The fossil example is also incompatible with "no-interbreeding" being a sufficient criterion, though this is a bit less clear than the bacteria example; we can't determine whether two fossils were or weren't able to interbreed. We can be nearly certain that there is some pair of structurally similar-looking fossils out there that we have labeled as belonging to a single species, despite the fact that the individual organisms wouldn't have been able to breed with each other. You could make the argument that this is simply a mistake on our part, and that would have a lot of validity, but even viewed that way it's a mistake that cannot even theoretically be corrected, which causes some conceptual difficulties. The reason there are so many species concept is that species are just a reflection of the idea that two organisms are "the same". What it means to be "the same" varies in different contexts, according to, without claiming to be exhaustive, (1) what you care about; (2) what is possible in the space you're discussing [pigs can't do the direct genetic exchange that bacteria can]; and (3) what it's possible for you to know. > I do appreciate this and I hope you don't perceive it as "arguing." Don't worry about offending me; you seem to be in perfectly good faith so far.

AlbertCory 2y ago
ok. If we know that a species (1) is sexual, and (2) cannot interbreed with an individual of a superficially similar species, then it IS sufficient to say we have two species there. I think I have all the qualifiers :) Incidentally, today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp." I pointed out that by that standard, we're also 60% the same as a banana.
- thaumasiotes 2y ago
  You might be interested in the concept of "ring species", which doesn't contradict the principle you just stated, but does conflict with the biological species concept. A ring species is a continuum of interbreeding populations such that the ends of the continuum are not interfertile. https://en.wikipedia.org/wiki/Ring_species https://en.wikipedia.org/wiki/Ring_species This parallels the phenomenon you see in languages where, for example, any two adjacent villages across a considerable distance will be able to speak to each other, even though villages at opposite ends of the continuum cannot do so. (The "ring" part of the term refers to the two ends of the interfertility continuum being located in the same geographic area, which is a red herring.) As the wikipedia page notes, the problem that this concept exposes is that interfertility is not a transitive relation, and therefore can't be an equivalence relation. > today on Facebook someone made the risible claim that since our DNA is 98% the same as a chimp, WE are "98% the same as a chimp." > I pointed out that by that standard, we're also 60% the same as a banana. The major problem here is that "to what degree is a person 'the same' as a chimp?" is not a well-defined question. Again, you would need to define what it means to be the same, and it will vary with what you care about. There are important ways in which we are the same as a banana; most obviously, you can eat a banana and expect to be nourished. This is not a given for an alien organism, even one that appears to be largely chemically identical to a banana. Whether the similarities reach 60% depends on how you convert them to numbers. We can note that the concept of 'species' assures us that any two humans are 100% "the same", as compared to a banana, whereas if you research relatedness the convention is that two brothers are 50% "the same" and two strangers are 0% "the same" (and bananas, not being human, don't exist), and if you're doing theology the convention is generally that even identical twins are 0% "the same". Summing that up, if you're told that two things are the same, the response is "the same how?" The reason the Facebook argument is stupid is that total shared DNA count isn't a useful thing to measure for most purposes. The salience of a difference in phenotype isn't closely related to the amount of DNA that changed to enable it.