We have a concept of âcarnivoreâ that is distinct from the order Carnivora. Animals that eat meat are carnivores even if theyâre not carnivorans, and there are herbivorous carnivorans. Carnivores are not monophyletic, carnivorans are.
We have a concept of âflying animalsâ that is not monophyletic (flight has evolved at least 4 times, gliding more). And as you note, there are flightless members of Aves.
Being nocturnal or diurnal is trait that has evolved many times that we have a name for because sometimes we care more about when an animal is active than what it descended from.
Having a polyphyletic concept of âswimming animalâ doesnât seem unreasonable to me, and âfishâ doesnât seem like a better or worse set of phenomes for it than any other. It will still have confusing edge cases (proto-whales? hippos? moose?) because biology is messy and gross, and the most useful definition will depend on the situation, and sometimes swimming will not be the only characteristic you care about, but itâs not unreasonable for the joint of reality you care about to sometimes be â100% aquatic with a body well adapted to itâ.
EDIT: my comment describes polyphyletic groups where the OP calls fish paraphyletic, which I missed because I found OP very hard to read and mistakenly remembered the common definition of fish to be polyphyletic. Iâm not sure how this changes the argument, but they plausibly should be treated quite differently, and if I want to argue they shouldnât I need to make that case.
To be sure, convergent evolution is a thing, such that sometimes we might want short codewords that point to the cluster-structure-produced-by-convergent-evolution rather than the conditional-independence-structure-produced-by-connectedness-in-phylogenetic-spaceâtrees, and possibly crabs, are a case in point. But itâs important to notice the differenceâto see through to the inferences your concepts are buying youâand what gets lost when you try to reason in a domain where your concept falls apart.
Zack, what are you claiming is lost? The straw-anti-phylogenist who headlines your post says:
Choosing to define categories around evolutionary relatedness rather than macroscopic human-relevant features seems like an arbitrary ĂŚsthetic whim.
This seems genuinely straw, relative to the simple position: â[Swimming-adapted animals] is a useful, joint-carving concept. [The clade containing all swimmers, minus the clade of landlubbers] is a useful, joint-carving concept. Sometimes one or the other is most suitable. If someone tells me Iâm supposed to use one or the other, when the alternative is more suitable, based on some simplistic policy of using words that are joint-carving in one way but not the other (rather than arguing suitability), theyâre just being silly.â Each of these concepts compresses cluster-structure in thingspace. You canât explain why dolphins and fish both propel themselves by undulating in a certain way by reference to phylogeny, you have to talk about adaptation to the vorticial behavior of water. You canât explain why dolphins breath air by reference to swimming-adaptedness, you have to talk about phylogenetic relatedness to air-breathers.
Certainly, there are lots and lots of different aspects in which things in the world can be similar, and we want our language to have lots and lots of concepts to describe those similarities in the contexts that they happen to be relevant in; if someone were to claim that carnivore shouldnât even be a word, that would be crazy, and thatâs not what Iâm trying to do.
Rather, Iâm trying to nail down a sense in which some concepts are more ârobustâ than othersâmore useful across a wide variety of situations and contexts. If someone asked you, âDo you have any pets? If so, what kind?â, and your pet was the animal depicted in the Wikimedia Commons file Felis_silvestris_catus_lying_on_rice_straw.jpg, you might reply, âYes, I have a cat.â But you probably wouldnât say, âYes, I have a carnivoreâ, or âYes, I have an endotherm.â You wouldnât even say âYes, I have a furry-four-legged-tailed-mammalââa concept which includes dogs, but which English doesnât even offer a word for! But all of those statements are true. Whatâs going on here? Is it just an arbitrary cultural convention that people talk about owning âcatsâ instead of endotherms or furry-four-legged-tailed-mammalsâa convention that could have just as easily gone the other way?
I argue that itâs mostly not arbitrary. (You could say that the convention has a large basin of attraction.) Cat-ness is causally upstream of carnivory and four-legged-ness and furriness and warm-bloodedness and nocternalness and whiskers and meowing and lots and lots of other specific details, including details that I donât personally know, and details that I âknowâ in the sense that my brain can use the information in some contexts, but of which I donât have fine-grained introspective access into the implementation details: itâs a lot easier to say âThatâs a catâ when you see one (and be correct), than it is to describe in words exactly what your brain is doing when you identify it as a cat and not a dog or a weasel.
I donât think Scott is claiming itâs arbitrary, I think heâs claiming itâs subjective, which is to say instrumental. As Eliezer kept pointing out in the morality debates, subjective things are objective if you close over the observerâhuman (ie. specific humansâ) morality is subjective, but not arbitrary, and certainly not unknowable.
But also I donât think that phylo categorization is stronger per se than niche categorization in predicting animal behavior, especially when it comes to relatively mutable properties like food consumption. Behavior, body shape etc are downstream of genes, but genes are cyclical with niche. And a lot of animals select their food opportunistically.
Phylo reveals information that niche doesnât. But niche also reveals information that is much harder to predict from phylo. I think Scottâs objection goes against the absolutizing claim that âphylo is all you need.â
âSwimming animalsâ vs. âfishâ seems like a fairly neutral term choice, so itâs somewhat boring as an example. Itâs a much bigger deal to choose between terms where one option has negative connotations and the other positive (or even just very different connotations!). Cf. various political debates over terms that shall not be named here.
We have a concept of âcarnivoreâ that is distinct from the order Carnivora. Animals that eat meat are carnivores even if theyâre not carnivorans, and there are herbivorous carnivorans. Carnivores are not monophyletic, carnivorans are.
We have a concept of âflying animalsâ that is not monophyletic (flight has evolved at least 4 times, gliding more). And as you note, there are flightless members of Aves.
Being nocturnal or diurnal is trait that has evolved many times that we have a name for because sometimes we care more about when an animal is active than what it descended from.
Having a polyphyletic concept of âswimming animalâ doesnât seem unreasonable to me, and âfishâ doesnât seem like a better or worse set of phenomes for it than any other. It will still have confusing edge cases (proto-whales? hippos? moose?) because biology is messy and gross, and the most useful definition will depend on the situation, and sometimes swimming will not be the only characteristic you care about, but itâs not unreasonable for the joint of reality you care about to sometimes be â100% aquatic with a body well adapted to itâ.
EDIT: my comment describes polyphyletic groups where the OP calls fish paraphyletic, which I missed because I found OP very hard to read and mistakenly remembered the common definition of fish to be polyphyletic. Iâm not sure how this changes the argument, but they plausibly should be treated quite differently, and if I want to argue they shouldnât I need to make that case.
Ditto.
This is addressed as a side-note in the paragraph
Zack, what are you claiming is lost? The straw-anti-phylogenist who headlines your post says:
This seems genuinely straw, relative to the simple position: â[Swimming-adapted animals] is a useful, joint-carving concept. [The clade containing all swimmers, minus the clade of landlubbers] is a useful, joint-carving concept. Sometimes one or the other is most suitable. If someone tells me Iâm supposed to use one or the other, when the alternative is more suitable, based on some simplistic policy of using words that are joint-carving in one way but not the other (rather than arguing suitability), theyâre just being silly.â Each of these concepts compresses cluster-structure in thingspace. You canât explain why dolphins and fish both propel themselves by undulating in a certain way by reference to phylogeny, you have to talk about adaptation to the vorticial behavior of water. You canât explain why dolphins breath air by reference to swimming-adaptedness, you have to talk about phylogenetic relatedness to air-breathers.
A potential crux:
I would also say:
but Iâm not sure youâd admit that, since the niche shows up in the causal graph in at best a cryptic way.
Certainly, there are lots and lots of different aspects in which things in the world can be similar, and we want our language to have lots and lots of concepts to describe those similarities in the contexts that they happen to be relevant in; if someone were to claim that carnivore shouldnât even be a word, that would be crazy, and thatâs not what Iâm trying to do.
Rather, Iâm trying to nail down a sense in which some concepts are more ârobustâ than othersâmore useful across a wide variety of situations and contexts. If someone asked you, âDo you have any pets? If so, what kind?â, and your pet was the animal depicted in the Wikimedia Commons file Felis_silvestris_catus_lying_on_rice_straw.jpg, you might reply, âYes, I have a cat.â But you probably wouldnât say, âYes, I have a carnivoreâ, or âYes, I have an endotherm.â You wouldnât even say âYes, I have a furry-four-legged-tailed-mammalââa concept which includes dogs, but which English doesnât even offer a word for! But all of those statements are true. Whatâs going on here? Is it just an arbitrary cultural convention that people talk about owning âcatsâ instead of endotherms or furry-four-legged-tailed-mammalsâa convention that could have just as easily gone the other way?
I argue that itâs mostly not arbitrary. (You could say that the convention has a large basin of attraction.) Cat-ness is causally upstream of carnivory and four-legged-ness and furriness and warm-bloodedness and nocternalness and whiskers and meowing and lots and lots of other specific details, including details that I donât personally know, and details that I âknowâ in the sense that my brain can use the information in some contexts, but of which I donât have fine-grained introspective access into the implementation details: itâs a lot easier to say âThatâs a catâ when you see one (and be correct), than it is to describe in words exactly what your brain is doing when you identify it as a cat and not a dog or a weasel.
(The relevant Sequences post is âMutual Information, and Density in Thingspaceâ.)
So while itâs true that the category of interest depends on context and the most useful definition can depend on the situation, concepts definable in terms of ancestry (but not even necessarily monophyletic groups) are so robustly useful across so many situations, that it makes sense that English has short words for cat and fish and monkey and prokaryoteâif these words didnât already exist, people would quickly reinvent themâand we donât suffer much from âsea animalsâ being a composition of two words. I think common usage is actually doing something right here, and people like Scott Alexander (âif he wants to define behemah as four-legged-land-dwellers thatâs his right, and no better or worse than your definition of âcreatures in a certain part of the phylogenetic treeââ) or Nate Soares (âThe definitional gynmastics required to believe that dolphins arenât fish are staggeringâ) who claim itâs arbitrary are doing something wrong.
I donât think Scott is claiming itâs arbitrary, I think heâs claiming itâs subjective, which is to say instrumental. As Eliezer kept pointing out in the morality debates, subjective things are objective if you close over the observerâhuman (ie. specific humansâ) morality is subjective, but not arbitrary, and certainly not unknowable.
But also I donât think that phylo categorization is stronger per se than niche categorization in predicting animal behavior, especially when it comes to relatively mutable properties like food consumption. Behavior, body shape etc are downstream of genes, but genes are cyclical with niche. And a lot of animals select their food opportunistically.
Phylo reveals information that niche doesnât. But niche also reveals information that is much harder to predict from phylo. I think Scottâs objection goes against the absolutizing claim that âphylo is all you need.â
âSwimming animalsâ vs. âfishâ seems like a fairly neutral term choice, so itâs somewhat boring as an example. Itâs a much bigger deal to choose between terms where one option has negative connotations and the other positive (or even just very different connotations!). Cf. various political debates over terms that shall not be named here.