I get this question all the time, and I just got asked it again: “Did you really say that humans are fish in that Ray Comfort video?” Yes, I did, and I guess I have to explain it again.
There are multiple meanings of “fish”. We can use it to refer to specific species or an extant category of animals: salmon are fish, halibut are fish, herring are fish. No one objects to that, and they all understand that if I said “humans are still salmon”, that would be wrong.
But another way the term is used is as a descriptor for a clade. A taxonomic clade is a “grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor”.
So, for instance, humans belong to the mammalian clade, which includes mice and cats and cows. If we have transhuman, part-cyborg descendants, they will still be mammals, because, note, by definition a clade must include all the descendants of an ancestor. We’re trapped! There’s no way our progeny can exit the clade!
We’re also members of multiple clades. For example, the tetrapod clade is the group that descended from a 4-limbed ancestor, an early amphibian, so it includes frogs and salamanders, and also reptiles, mammals, and birds, and the fact that we’re weird bipeds that have specialized our two pairs of limbs in odd ways, or that birds have turned a forelimb into a wing, doesn’t get us out of the club labeled “four footed”.
The thing about the clades of mammals and tetrapods, though, is that we have convenient generic labels for the groups: we can say “humans are mammals”, and we don’t get hordes of clueless people gawping and saying, “Did he just call me a mouse? That’s absurd!” But we belong to another clade, all the organisms descended from an ancient fish, and “fish” is the common label there. People generally have such a dim comprehension of the diversity of the fishes, though, that they hear a biologist pointing out that we belong, and will always belong, to the fish clade, and they think, “Did he just call me a sturgeon? That’s absurd!”
One way to get around the problem is to get technical. I could say we’re all gnathostomes, and nobody would freak out because most of them wouldn’t have the slightest idea what I was talking about. So I could hide in technical obfuscation. But the point is that you are descended from an ancestor that was a torpedo-shaped aquatic vertebrate with gills, a fish. You can never escape your ancestry. Embrace Your Inner Fish.
By the way, another way “fish” is defined taxonomically is as a craniate that is not a tetrapod, and if you use that definition, we are not fish. But that requires explicitly creating a paraphyletic group (that’s what you call it when you take a clade and willfully exclude a smaller clade), and that’s just annoying.
That’s my objection to people who say we aren’t [descended from] monkeys, usually to shut creationists up. I may be out of step here, but I like to think everyone will be retiring paraphyletic categories in future.
For one thing, we’re all simians here, and we’re only “tailless” on a technicality: sometimes we ARE born with tails, because we’re monkeys.
For another thing, the common ancestor of humans and monkeys (but not tarsiers) was a dry-nosed simian primate with a tail, which means it was a monkey by even the paraphyletic definition.
I’m not sure if this is standard among biologists, but I recently had the annoying experience of arguing with a creationist only to have my ally turn on me and define “monkey” not only to exclude tailless varieties, but also to exclude extinct varieties, and insist that the common ancestor of simians was not a monkey, and neither was the last tailed ancestor of the apes. He threw away a teachable moment so he could win the argument on a technicality.
#1 A Masked Avenger
Most evolutionary biologists, at least, know what PZ was talking about. But there are a few who don’t. Francisco Ayala, for example, wrote a whole book with the title Am I a Monkey?, and his answer was “no”. But I’d say he was the exception.
Was your “ally” a biologist?
Grammar police here: “paraphyletic clade” is self-contradictory, since clades are by definition monophyletic. “Paraphyletic taxon”, perhaps.
Another pet peeve of mine is when people say “monophyletic clade”. That’s like saying “canine dog” or “hydrogen-containing water”. There’s no other kind.
So then is dinosaur a clade in this sense? I’ve seen it used both ways: category ‘dinosaur’ starting a few hundred million years ago and ending 65 million years ago; and also as a category starting a few hundred million years ago and continuing to the present, with birds included as ‘dinosaur.’ So, is it paraphyletic or not, and whatever that answer may be, why is it used both ways?
Non-scientist reaction to this: I love the idea of being connected/related to much of the world’s living creatures, past, present, and future, even very, very distantly. It is very cool. Perhaps if more people could accept that concept and find pleasure and wonder in it instead of revulsion, then we would do better to protect all species and to take better care of our world, where we all must live together.
I am not a biologist, but isn’t the human coccyx (“tail bone”) essentially a tail? Vestigial, but present nonetheless?
Again I can’t understand the revulsion that some people seem to feel when presented with (reminded of) the concept that people are animals. Perhaps it has to do with the negative connotations that have developed around the word “animal” — messy, ungoverned, savage, brutish, mean, etc. — and people don’t want to be associated with any of that. But of course non-human animals don’t have any of those human characteristics — they simply are what they are, they do what they do, and it is entirely nonsensical to assign human values to animal behavior, as it is nonsensical to deny that humans are animals.
There’s always the alternate answer: there’s no such thing as a fish.
Since there’s pretty much no cladistic category that could include everything we call a fish and exclude any exclusively land-dwelling animals.
Holmes @4:
Very well-read layman’s answer: Yes and no.
Yes, Dinosauria is a clade. But only if it includes Aves. Keep in mind that the following is written by an historian who reads palaeontology as a hobby.
Archosauriformes are a clade which includes the extinct Phytosaurs, Aetosurs, Rauisuchids, and Crocodylomorphs (including modern crocodyles, caimans, and alligators), PLUS Ornithodira. Basically, this clade could be defined as the last common ancestor of the house sparrow and alligator, plus ALL descendents. This clade includes not only the ancestral antorbital and mandibular fenestra, but also a parasigittal stance and one-way flow-through lungs.
Ornithodira includes Pteraurisa plus Dinosauria. Basically, this clade is can be defined as the last common ancestor of the house sparrow and a late-Cretaceous pterasaur and ALL descendents. This clade includes the ancestral conditions of Ornithodira, and adds elongated tibiae and metatarals, as well an S-shape curve to the neck.
Dinosauria includes both Saurischia and Ornithischia. This clade can be described as the last common ancestor of Triceratops and the house sparrow, and ALL descendents. This clade includes the ancestral conditions of Ornithodira, but adds elongated pubic and ischial processes.
Ornithischia includes Heterodontosauridae, Thyreophora, Ornithopoda, and Marginocephalia. These are the bird-hipped dinosaurs. This clade can be defined as the last common ancestor of Pisanosaurus and Triceratops and ALL the descendents.
Saurischia, the lizard hipped dinosaurs, include both Sauropodomorpha and Therapoda. Therapods can be described as the last common ancestor of Herrerasauria (assuming Herrerasaurus is actually a Theropod, and there is quite a bit of argument going on about this) and the house sparrow and ALL the descendents. Aves is merely a clade nested within Avetheropoda which nests within Tetanurae which nests within Neotheropoda, which nests within Theropoda, which nests within Saurischia, which nests within Dinosauria, which nests within Ornithodira, which nests within Archosauria.
All of these (Aves, Avetheropoda, Tetanurae, Neotherophoda, Theropoda, Saurischia, Dinosauria, Ornithodira and Archosauria) are valid clades (though it sometimes seams that every new discovery, when run through the PAUP software, comes up with a reshuffling of the whole thing) if, and only if, the clades nested within are included.
If one defines Dinosauria as Saurischia plus Ornithischia, but no including Aves, it is not a valid clade (it would be like the illustration in the OP with the yellow box). If one includes Aves, then yes, Dinosauria is a valid clade. The clade is the last common ancestor of two specific species, and includes all descendants, extant or extinct — the last common ancestor of Triceratops horridus and Passer domesticus and all descendants comprises the clade of Dinosauria.
When laymen or professionals discuss dinosaurs, they are generally discussing the extinct Mesozoic animals that have fascinated me since I was four years old. If we use the actual clade name, Dinosauria, then, by definition, we are included the sub-clade of Aves.
Does that make sense?
And sorry for the Teal Deer and the multiple homages to Tpyos. I think I may have mixed up a couple of clades (I don’t have my books with me right now). Sorry in advance to the actual professionals.
Brother Ogvorbis
Your only error that I can see is that you have given the definition of Archosauria but called it Archosauriformes. The latter is a more inclusive group.
John Harshman:
Damnit!
So… ‘Dinosauria’ is a clade by definition, while ‘dinosaur’ may or may not be a clade, depending on the context of the discussion – which is only discernable if you are knowledgeable in the subject or psychic – and also depending on whether the speaker was using the term carefully or sloppily.
I have sympathy for those that find ‘fish’ annoying.
“By the way, another way “fish” is defined taxonomically is as a craniate that is not a tetrapod, and if you use that definition, we are not fish. But that requires explicitly creating a paraphyletic clade (that’s what you call it when you take a clade and willfully exclude a smaller clade), and that’s just annoying.”
Or you could just call it a grade. The vernacular understanding of fish is a grade. Same for reptiles.
Holms: yep. But I think we will pretty soon be referring to birds as dinosaurs. Lots of folks refer to the poor beggars who died out 65 mya as “non-avian dinosaurs.” We may still use “dinosaur” paraphyletically based on context, in the same way that I (despite my rant in #1) would be annoyed if people insisted on always referring to monkeys as “non-ape monkeys.”
When Francisco Ayala wrote in his recent book that we weren’t monkeys, he was using the older Mayr-Simpson view, under which groups in the classification system don’t have to be monophyletic. They allowed birds and reptiles to be separate classes, even though the common ancestor of reptiles was also an ancestor of birds. Almost all systematists these days would disagree with this view.
When I have spoken to audiences of nonscientists, I have agreed with PZ that we are not only descended from monkeys, we are monkeys. That we are descended from monkeys would be easier to accept if the common ancestor of all monkeys, which is also out ancestor, were around. As it walked by, our brain would keep thinking “there goes a monkey”.
PZ, your descriptions of biology are invariably wonderful and clear. I do hope that many of them are going to appear in your new book.
Where this gets weird is that whales/dolphins etc are mammals but.. ALSO FISH. Penguins are dinosaurs AND fish. Its a fish-eat-fish world out here. Only thing Im missing is the land-dwelling cephalopods but then I usually get them wrong.
Holms @11:
I think jaxkayaker @12 has it right. Dinosauria is a clade, dinosaur is a grade within that clade.
A Masked Avenger @13:
I tend to refer to birds as avian theropods. In many of the books I read (currently reading The Age of Dinosaurs in South America, Novas, 2009), the term “non-avian theropod” is often used early in a publication, with a footnote or parenthetical that, from this point on, unless discussing a genus within the Aves clade, the author will just use “theropod”. I’ve run into “non-avian dinosaurs” in conversation but haven’t run into it in print.
=8)-DX @15:
Took me a few minutes to wrap my mind around this, but, yeah, you got it. The clade that could be defined as the last common ancestor of a specific species within the clade Chondrichthyes and a specific species within the clade Aves could be referred to Pisces. It messes with my little liveral arts mind that although Tetrapoda is a valid clade, it nests within Crossopterygii and Pisces, and a theoretically uncountable number of other clades all neatly nested within each other like those RUssian dolls.
And Archosaurs, and Ornithines, and Saurischia, and . . .
Yeah, well, those are the Invertebrates, specifically the Cephalochordates (I think?). And I seem to remember reading a paper about the invertebrate fossil assemblages in Alberta’s Dinosau Provincial Park that showed that the land-dwelling cephalopods are a not a valid clade as there are multiple lineages that left the water on their own.
META: THis is so much more fun than arguing with InDesign.
@16 Do you mean terrestrial mollusks? AFAIK, cephalopods are exclusively marine.
Brother Ogvorbis
Cephalopods (octopuses) are mollusks, whereas Cephalochordates are creatures with a notochord and dorsal nerve cord and are a sub-phylum within the phylum Chordata. I believe. At least they were back in the day.
Gwen Sutton @17:
I was answering =8)-DX further up and, doing this from memory, my answer went weird. Though there is the href=”http://zapatopi.net/treeoctopus/”> rare and endangered Pacific Tree Octopus?
procyon @18:
Yeah. This is what happens when I do this stuff out of memory. I don’t have my library with me, so chalk it up an old man’s faulty memory.
And I screwed that one up. The Pacific Tree Octopus can be found here: http://zapatopi.net/treeoctopus/
Why is there an extra hand on the right sleeve of the human in the image?
I recently watched that entire Ray Comfort Evolution vs. Godd video (a creationist nicely asked me to) and I was struck by the interviewer’s response to “we are fish.”
No response. Iirc, the film just cuts away and leaves it there.
A normal, ordinary person in an actual conversation would have asked “Why?” They might have prefaced the question with “that’s ridiculous” — but they still would have asked it. And then they would have learned something — if only what you meant. A normal reporter doing an actual interview would have quickly followed your statement with the obvious response: “… And what can you possibly mean by that, Dr. Myers?”
One additional clue — if one were needed — that this is propaganda, not a real documentary. The atheist professor has no reason, audience, he’s just stupid and saying stupid stuff so here’s where you laugh and then we go to another edited soundbite from another evolutionist loser.
Holms @#4:
When I was in grade school in the 60s, we were taught that ALL dinosaurs were extinct and that birds descended from reptiles, not dinosaurs. Add that to the then-popular portrayal of dinosaurs as giant, lumbering, and naked (no feathers), and it’s easy to see why we older folk tend to think of birds as entirely separate from dinosaurs. Younger people are much less likely to make that mistake, I think.
Here’s what I keep wondering: are we bacteria?
(Honest question. Didn’t we ultimately descend from them?)
So my grand-dad was a monkey, and his grand-dad was a fish?
What a complicated, ancient family tree!
I can trace my mother’s side to amphioxus, if you wish,
Though they won’t admit they’re relatives of me.
http://freethoughtblogs.com/cuttlefish/2011/02/12/wait-im-the-black-sheep/
Lady Mondegreen @24:
We are Eukaryotes. Along with plants and fungi. And a slew of single-celled organisms.
Bacteria branched off into their own kingdom well before Eukarotes and Archaea split. And I have no idea what the last common ancestor of a bacteria and a human would be. Would it be a bacteria? Would it be something that fit into no neat niche in the tree of life? Not sure.
I love reading these comments.
Thanks, Brother Ogvorbis.
Bactera, Eukaryotes and Archaea are domains. Maybe the Russian-nesting-doll system of cladistics stops at the kingdom level.
Rather, at the domain level.
@24
We are all in the clade of life….organisms with DNA
Ogvorbis:
I have not only seen “non-avian dinosaur” in print, I have been involved in producing some of the books in question. My former employer published (among other things) science review books for middle school and high school students. That meant trying to cram a lot into a relatively small space, trying to fit the various state standards (which the students were going to be tested on) without being either confusing or inaccurate. So the K-T extinction was referred to as having wiped out the non-avian dinosaurs (among other organisms), because that’s a short way to refer to the group in question.
Since “non-avian dinosaur” isn’t a formal taxonomic term, it doesn’t matter that it’s paraphyletic.
Since a lot of folks here have various questions about how group a is related to group b, etc, I thought I would link to a wonderful resource that I believe many here should appreciate. It is basically a interactive tree of life that is continually being worked on and eventually plans to include all living organisms and show how every living thing is related!
Since many are curious how we descended from fish, I will link to the starting point from when tetrapods branch off from fishes.
http://www.onezoom.org/life.html#sarcopterygii
The tetrapod part is not surprisingly, also the most complete so you can spend hours alone on just this part of the tree of life! Really impressive work that they have accomplished over there.
“Bacteria branched off into their own kingdom well before Eukarotes [sic] and Archaea split.”
“Here’s what I keep wondering: are we bacteria?
(Honest question. Didn’t we ultimately descend from them?)”
Current evidence suggests that the first life forms were prokaryotes, which Bacteria and Archaea are. These two lineages are the earliest arising clades among the three domains. A merger between a species of Bacteria and a species of Archaea resulted in the first species of domain Eukarya. The proto-eukaryote was a cell of Archaea containing a cell of the Bacteria. The bacterium evolved into the mitochondrion, with substantial transfer of that bacterium’s genome to the genome of the archaeal cell. Consequently, the domain Eukarya is a clade itself, but not comfortably nested within Archaea or Bacteria, as it resulted from the merger of species from each.
Thanks, jaxkayaker!
I <3 my inner Tiktaalik. :)
Gulp. Can I get a part in the next Finding Nemo movie? Gulp.
Am I missing something or is there a reason why the blue and pink rectangles miss the branching points? It would be clearer to me if they included them, but I fear I may be missing a subtlety.
If the blue rectangle included the branching point and only the same line it currently has, then some of the descendants of the common ancestor species (which is what the branch point represents) would be left out, and therefore the taxonomic group represented by such highlighting would not be a properly constructed clade (i.e. would not be monophyletic). In that case, it would represent the same situation shown by the tree with the orange rectangle: a paraphyletic taxonomic group. Paraphyletic groups are invalid according to cladistic analysis. The pink rectangle is a different improper grouping; it’s polyphyletic. If the pink rectangle were expanded to include on or both the immediately preceding branch points, but no other lineages, it would still be polyphyletic. If the pink rectangle were expanded to include both immediately preceding branch points and also the lowest (earliest) branch point, the grouping would be paraphyletic. Still improper, but in a different way. Generally, paraphyletic groupings are missing descendants of a common ancestor, while polyphyletic groupings are missing common ancestors that would unite the species in the group. Note that the ancestors are inferred and not directly observed.
Brother Ogvorbis, Fully Defenestrated Emperor of Steam, Fire and Absurdity@7,
So, birds nest within dinosaurs, and not in trees, as commonly believed :-p
Photographs of a sturgeon.
@jaxkayaker #38. Thank you very much. Your explanation nailed it for me.
I agree that from a cladistic, genetic, and anatomical standpoint it makes sense to think of humans and other tetrapods as heavily derived, modified fish. That doesn’t mean that saying outright that humans are fish without qualifying it isn’t opening yourself up to creationist spin doctoring.
On the diversity of fish, I actually do wonder about how distantly related groups like lampreys and hagfish are from jawed fish compared to how distantly related jawed fish are from tetrapods. I wonder if humans are more closely related to one group of fish than each group of fish are to each other.
Going right back to the top, are the members of a clade individual organisms or species?
For arguing with creationists it makes more sense to talk about individuals rather than species / kinds / rescued-by-Noah-subsets, but if a clade is composed of individuals then doesn’t sex mess up the “most recent common ancestor” unless you specify a female or male line of descent?
A Masked Avenger @13: I (despite my rant in #1) would be annoyed if people insisted on always referring to monkeys as “non-ape monkeys.”
Ook!
Vicki @31:
That makes sense. I do have some palaeontology text books, but all are at the college level. That phrasing makes perfect sense for the middle and high school level. And thank you for your work helping to provide reality-based biology texts for the schools.
Nick Gotts @39:
One of the books I have (no idea which one it is?) has an older etching showing an Iguanodontian perched in a tree. So. . .
Bob Dowling @42:
I think this is part of the whole Matrushka dolls idea: An individual is one of many members of a species (could the species level be considered a clade itself, especially considering all of the subspecies and ‘breeds’ of, especially, domestic animals?); each species is one of (possibly) many species within a genus — the genus is a clade on its own. The genus is part of a larger clade, which is part of a larger clade, which is part of a larger clade, and so on and so on and so on.
#41 emergence:
Wonder no more. To use the terminology of this post, tetrapods are jawed fish. Without them, “jawed fish” (Gnathostomata) isn’t a monophyletic group. Tetrapods (including humans, of course) belong to a group within jawed fish called Sarcopterygia, which also includes lungfish, coelacanths, and a lot of extinct groups like panderichthyids. So you’re closer to a lungfish than to a carp, closer to a carp than to a shark, closer to a shark than to a lamprey.
For more details, try this.
#37 lewisx:
Those aren’t branch points. The branch points are the places where a vertical line joins a horizontal bar from which two more vertical lines proceed. The vertical lines are lineages, but the horizontal line is just a meaningless graphic device to let you know that the vertical bits have separated. So those elbows in the trees aren’t branch points at all. In fact, trees are often drawn without those elbows, just with slanting lines emerging directly from the branch points.
John, how do you know Lewis was referring to the “elbows” when he asked about the branch points?
@John Harshman # 46. I did understand the branching points to be the points where the verticals meet the horizontals and I was not referring to the elbows.However my question betrayed enough confusion that I appreciate you making absolutely sure we are on the same page. That’s an interesting point about angled lines from branch points which would avoid this potential confusion (at least for people like me). For some reason my brain derailed, whilst trying to square PZ’s (retrospectively very simple) definition of a clade with the pink and blue rectangles not encompassing branch points as the orange and green rectangles do. Jaxkayaker’s explanation, in exploring the implications of the blue and pink rectangles being expanded to the branch points, knocked the bogeys back onto the tracks and gave me more insight at the same time. :-)
Thank you both.