Eels are fish

Apparently we are all fish. Or fish don't exist.

To explain: if you want to define a taxonomy in which all things that look like fish and swim are 'fish' then we are too. We are more closely related to most 'fish' than sharks are. I.e the last common ancestor of herring AND sharks is older than our & herring's LCA.

At least you could exclude jawless, cartilaginous, and lobe-finned fish. That would leave you with 99% of what people call fish. But as said it would exclude sharks, they would need to be their own group.

More bothering me is that there are no trees. There are just many plants which have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight.

For reference, this idea is becoming more popular recently due to the Green brothers: https://youtu.be/-C3lR3pczjo

> Apparently we are all fish. Or fish don't exist

Apparently if you go even further back and apply the same logic, we are all fungi. In fact, we both can synthesize vitamin D from sunlight, although I'm not sure if we do it the same way or use it for the same purpose.

I could be way off base here, and I don't honestly know much about biology... but just because two species don't have recent common ancestors, doesn't mean they couldn't have co-evolved and ended up very similarly, right? Wouldn't this be grounds for relating their classification?

Yeah. Terms like "fish" and "tree" are more like "quadruped" than they are like "rodent".

Yes, fish, like trees or reptiles, don't exist as a monophyletic group (or clade).

Convergent evolution happens all the time but taxonomy is nonetheless based on ancestry.

> things that look like fish

Well, apart from the circularity, we don't look like fish, do we? What we look like, we define, just like we define what 'fish' is. There's no need to go all Linnaeus about it.

This is just a consequence of life beginning in the ocean. Land-based life is related to ocean-based life at the point of the fork, and there were prior forks which, by definition, remained in the ocean.

Does this hold even if we don't include whales and dolphins in "things that look like fish"?

My stance is somewhat similar, I think? Arguments that try and precisely define "fish" in some sort of "context free" space are doomed because people don't think of terms outside of context.

Looking at the Wikipedia article for fish, it looks like a reasonable definition would be:

* Everything in the subphylum vertebrata (i.e. vertibrates)

* Except tetrapoda (tetrapods: amphibians, reptiles, mammals and the like).

It's not perfect because tetrapoda does fit within vertebrata in a biological / genetic sense (as a sibling comment put it: fish is not a monophyletic group). But it's a precise enough definition that I don't think we need to claim that we're all fish or that there's no such thing as a fish (as the QI elves would say).

For a fun somewhat related topic, it was neat to see the hierarchy of strings and characters in Common Lisp the other day. Can be used to illustrate a bit of the shortcoming of using ancestry to answer if two things are related. https://lispcookbook.github.io/cl-cookbook/strings.html#stri...

Yes, the issue is the ancestry between "fish" being very distant. It doesn't matter if you exclude marine mammals. Many fish in the ocean are still more closely related to beings on land than another fish. It's the equivalent of calling all flying animals birds. If we excluded bats from this new definition of "bird" then a bumblebee won't suddenly become more closely related to a Buzzard.

Fish exist, and we're not fish. Fish just isn't a monophyletic taxonomic category. If you allow "fish" to be a list of all those animals that look like "fish" and swim like "fish", you'll end up with a bunch of animals who's most recent common ancestor is also the most recent common ancestor of all tertrapods (including humans), so "we are all fish". But if you don't demand a single common ancestor & instead just have a list of several different taxonomic classes you can define "fish" as anything in the list, thereby excluding humans.

It's like the difference between culinary berries (sweet parts of plants) and biological berries (parts of plants containing the seeds internally). Tomatoes are not a culinary berry, but are a biological berry. Strawberries are a culinary berry, but not a biological berry (the seeds are on the outside). It's confusion caused by mixing a jargon use of a word with the common use of that same word.

But what about our precious friends the coelacanths?

Edit: foolish me coelacanths are not tetrapods

But a better question may have been regarding the lungfishes

Also "horizontal gene transfer" happens in bacteria, and even happens in multicellular sexually-reproducing organisms after viral infection in some cases. Taxonomy should be a directed acyclic graph, not a tree.

Those aren't the problem. The real issue is that the tetrapods which evolved into most land animals (amphibians, reptiles, birds, mammals) are further down the phylogenetic tree of bony fishes than coelacanths and lungfish, which are further down the tree than cartilaginous fishes like sharks and rays, which are further down the tree than jawless fishes like lampreys and hagfish.

In taxonomy, it's called a "Paraphyletic group" [1].

[1]: https://en.wikipedia.org/wiki/Paraphyly#Examples

Mammals include orcas and whales

Not a surprising result given that complex sea life significantly predates complex land life. It's had much longer to genetically diversify.

Similarly either we are all black, or black as a genetic race doesn't exist. The genetic diversity within humans in Africa exceeds the diversity outside of it. You can find two "black" Africans that are more genetically different than an Australian aborigine compared to a red headed Irishman.

And orcas and whales are not fish.

It surely does. This website is a good way to visualize the common ancestor of the bottlenosed dolphin and zebrafish. It's the same common ancestor as a human and a zebrafish, or a bird and a zebrafish. It's an ancient ancestor!

https://www.onezoom.org/life/@Gnathostomata=278114?otthome=%...

It's much more valid for trees. They've evolved many times and there is no common ancestor that is itself a tree.

Fish evolved once, and then a specific subgroup is excluded. That's fine.

There's a certain species of ape that takes offense at this, and doesn't like to think of itself as a "fish".

> Apparently we are all fish. Or fish don't exist.

I get very annoyed at this argument. It pretends that the only classification systems are strictly following a single ancestor or ignoring ancestry entirely.

The common definition of fish is neither of these. It's paraphyletic. Everything descended from A, except things descended from B and C.

But what about bees?

https://www.loweringthebar.net/2022/06/court-says-bees-are-f...

Human embryogenesis would like to disagree with you.

https://www.bbc.co.uk/news/health-13278255

Or the book "why fish don't exist", which got a lot of press last year if you consume media outside of youtube.

You should have used "phylogenetic taxonomy". A "taxonomy" is literally any way of grouping organisms, like "all red things" (mature salmon, some roses, red algae).

They could have a similar phenotype without being genetically similar.

Except that "quadruped" is (AFAIK) phylogenetic: Tetrapoda.

Evolving from doesn't make you the thing, does it? It makes you something else. Fish in particular, since that's a group of animals named by us, based on physical appearance.

Not sure of that last claim, as Australian natives are (AFAIK) considered one of the very oldest groups to separate from other Homo sapiens. IIRC, they're the only major group that has no Neanderthal DNA, because they migrated/were separated before H. sapiens met H. neanderthalis.

That's a month old. I heard it over a year ago.

You know what I say to that? Go back to Sumatra, ya ginger galoot!

"I want to be like you-u!" Yeah, right.

Fungi and Animalia split from Eukarya. Fungi didn't exist before then.

I realize "we are all eukaryotes" doesn't have the same punch...

Ontogeny does NOT recapitulate phylogeny.

Exactly.

But I believe in weak Haeckel's principle.

> Evolving from doesn't make you the thing, does it?

Depends on the system of taxonomy; in phylogenetic taxonomy, that’t exactly how membership in a clade is determined.

Except that you can come up with a decent definition of "fish" and "quadruped", whereas there's no definition of "tree" that covers all the cases.

https://www.theatlantic.com/science/archive/2018/04/how-do-y...

First of all: I think it's ok if the definition of fish is a bit blurry around the edges.

But actually I think coelacanths are quite a fun example. I hadn't heard of these before, thank you!

Yes, they're not tetrapods, but (I've just discovered) they're not even vertebrates (no spine). According to my definition, they shouldn't be fish, but they do seem quite fish like.

They are chordates (they have a spinal cord, just no backbone for it), so I could expand my definition to any chordate that isn't a tetrapod. But there are some rather non-fishy chordates [1] so that doesn't work either.

[1] https://en.m.wikipedia.org/wiki/Tunicate

(For those that don't know, the top level subclassification of animals is phylum. There are a lot of phyla but a common ones are chordates (all vertebrates plus a few odd animals like discussed above), arthropods (insects and insect-like things like spiders and crabs), and molluscs (like slugs and clams). When I was at school, animals were just vertebrates or invertebrates but the reality is more interesting. I went down that rabbit hole when I found out that, weirdly, octopuses are molluscs.)

They're not taxonomically fish (even if you want a monophyletic category & thus count mammals as fish), they're not colloquially fish, they're legally fish under California Fish & Game Code § 45, but they're not necessarily legally fish in other jurisdictions or other subsections of the California Fish & Game Code. Because laws also define words to create jargon, and thereby new meanings dissociated from their common use. The extra fun bit is that other parts of the law can choose to define "fish" differently, for other purposes. Jargon has scope, and allows overloading.

There are lineages in Africa that split from other lineages in Africa before the Australian aborigine split. Add on more frequent (but still rare) mixing for even more diversity. Mixing makes the majority more homogeneous but can increase diversity at the extremes.

> * tetrapod (/ˈtɛtrəˌpɒd/;[4] from Ancient Greek τετρα- (tetra-) 'four' and πούς (poús) 'foot') is any four-limbed vertebrate animal of the clade Tetrapoda (/tɛˈtræpədə/).*

Huh. I always thought it was a more generic term for any four-limbed animal. TIL, I guess!

> They are chordates (they have a spinal cord, just no backbone for it)

None of the cartiligenous fish have backbones. Nor any other bones.

Coelacanths have backbone-functioning cartilige.

Honestly, I can't think of a non-tetrapod animal that is four-limbed. I mean, unless you cut one leg off a starfish.

We are also fairly closely related to fungi, which is why it’s tricky to make good systemic fungicides. They always go after the liver.

Melanin apparently predates the split between fungus and animal kingdoms.

> Fish exist, and we're not fish.

Sudden flash of A Shadow over Innsmouth.

Orcas and whales are flip floppers (no pun intended).

We left the water and they went back. (I have a theory that given enough time, Labrador retrievers would form a new branch of marine mammals with similar morphology to seals).

There is an entertaining book related to this. Why Fish Don't Exist by Lulu Miller.

https://www.goodreads.com/book/show/50887097-why-fish-don-t-...

> Fungi and Animalia split from Eukarya. Fungi didn't exist before then.

Plants are also Eukaryotes but Fungi and Animalia have a more recent common ancestor than either has with Plantae.

We and fungi are both Opisthokonts, a distinct subclade of Eukaryotes, but plants are not.

https://en.m.wikipedia.org/wiki/Opisthokont

But literarily (not literally) they can be.

See also https://slatestarcodex.com/2014/11/21/the-categories-were-ma...

Whales are fish that spout and have horizontal tail fins. (Currently re-reading Moby-Dick and that's the definition Ishmael comes up with.)

The correct conclusion to take from this is that cladistics supremacists are wrong and there are other valid ways of organising knowledge.

I think it's ok for there to be two meanings of "fish": a biologically formal (but not perfect) definition like I gave in my comment above, and a more informal meaning of "animal thing in the sea" that includes whales and even "starfish". It's very common for words to face more than one meaning. But that doesn't mean you can invalidate one by referring to the other.

So politicians are reptiles after all?

I have multiple meanings of "fish", and that's ok.

But none of them include marine mammals such as seals, dolphins and whales. And none of them include penguins, even though penguins flying through the water on their little wings are impressively graceful and fast. None of these animals are fish to me under any meaning of the word.