I did mean “need not”.
And I hate to quibble about this, but there is no reason that a “rigorous, systematic classification” can’t be a polyphyletic one. We have chosen to rely more and more on cladistics, which is monophyletic. But that’s a choice we make, not something that is objectively correct.
I’ve been avoiding the ape issue by just saying that my ancestors lived in trees and had very long arms as I do to better reach waaaaay out to pick that elusive fruit on the outer limbs. I think they get the idea without confusing them with semantics.
Here I think you may mean paraphyletic rather than polyphyletic. But either way, as I understand all these terms to be used with respect to modern biology, I disagree.
“Systematic” specifically means relatedness tracked through diversification over time. Polyphyly has nothing to do with relatedness; it’s just a description of similar extant characteristics–like calling a koala a “bear.” Paraphyly starts with relatedness, but it’s not rigorous, because it takes subcategories out of categories for no objective reason. Paraphyletic terms are the “layman’s terms” above–like using “ape” to mean hominoids excluding humans.
That is, no objective reason that is rigorously systematic.
It is true that Sarcopterygii is a “Subclass” while Tetrapoda is a “Superclass”, but that just illustrates why I consider the ranks to be meaningless: they actively obscure information regarding evolutionary relationships. Which, in this case, is the opposite of the ranking: clade Tetrapoda is within clade Sarcopterygii (the former having evolved from ancestors within the latter).
There are some folks (such as paleontologist Michael Benton) who keep the ranks, while still trying to organize groups by clade, resulting in silliness like this example where the higher-ranked group is subsumed within the lower-ranked one. I prefer to ditch the ranks entirely, personally.
Thank you for the clarification.
So, my delineation of the “fish” classification above was a little off, but I guess the general point remains.
Why not just (re)assign ranks according to the hierarchy of the clades? I mean, if the systematic hierarchy is there, why not reflect this in the widely-understood (if, to date, imperfect) rank structure?
I kinda thought that’s what people were doing, and was part of the reason why so many new intermediate-ranked taxa have been introduced in recent years.
This is getting a bit far afield from the OP’s question, but there are a number of problems with that, unfortunately.
Firstly, the current rankings are too ingrained to change them. Try downgrading Aves from the rank of Class and see what happens…
Secondly, there are only so many prefixes to go around without it just getting downright silly. Cladistics assumes a branching pattern of evolution, so every single speciation event could, in theory, be assigned to a node, and that node given a name. Again, consider the current taxonomy of birds. Now, put that taxonomy in its proper evolutionary context (birds descended from dinosaurs, which are reptiles), and try to come up with sufficient rank prefixes or even new ranks to accommodate all of that, given Reptilia is also its own Linnaean Class, and Dinosauria itself has been proposed as a distinct Class. Because ranks are a holdover from Linnaean taxonomy, which was gradistic rather than cladistic (that is, relied more on morphological grades based on appearance than on any concept of evolutionary relatedness), we’d pretty much have to scrap the entire system and start over in order to incorporate rankings into current taxonomies.
Thirdly, the ranks add no new information. If one is already familiar with the hierarchical placement of the nodes in a cladogram, then further assigning of ranks to those nodes doesn’t tell you anything new. And really, that’s kind of the whole point of classification: the name itself should provide information about the group it represents, since it is effectively a shorthand for the diagnostic characters that the node represents.
Fourthly, if anything, ranks obfuscate diversity, since there is no proper definition for any given rank. A Family can contain one or a hundred genera. An Order can likewise contain one or a hundred families. One could, in theory, have an entire Phylum containing but a single species. As such, even if one knows that such-and-such node has been ranked at the level of Family, one cannot make any meaningful comparisons of relative diversity to any other Family. Or really, any meaningful comparison at all.
All in all, then, in my opinion, it’s just not worth the extra effort. The nodes, presumably, are “natural” (being, as they are, based on synapomorphies, or shared derived characters). We assign the nodes a name for convenience. But anything beyond that is superfluous.
If you mean “ape” to describe a clade, humans are apes, full stop. Many terms for living things are not cladistic (or phylogenetic)–but descriptive. “Fish” is the most obvious, but “reptile,” “monkey,” and “dinosaur” as commonly used all describe groups that are not generally defined to coincide with clades. Cladistics aint’ everythin’.
“Ape” tends to be used for hominoids that are not Homo, but I for one tend to call humans “apes” and even “monkeys” (loosely) anyway.
I understand that under the “strict” definition monkeys are a subset of not-quite-ape primates (and include members of at least two different clades).
Apes are either a subclade of the clade that includes monkeys, or a term for members of that clade that are not quite humanoid. It depends on the context. You can keep calling us apes as far as I’m concerned.
But we’re not lobe-finned fish. We derive from the same clade, and are distantly allied to lobe-finned fish. But our branch stopped being fish a long time ago. That’s why we have classification terms that are not clades.
Can we a see a cite to back that up?
Your mitochondria are structurally similar to Monera (which is the kingdom name I learned for bacteria over a decade ago). Eukaryotes as such are pretty far from Monera. It would be a tiny bit like saying a car is a hominid because it has a human driver inside it.
I think you mean to say, “phylogenetic systematics” means relatedness tracked through diversification over time.
And there’s a great difference between calling a koala a bear and calling a human a monkey or calling an ape a monkey. Koalas and bears proper are really different in general morphology, behavior, and yes, phylogenetics. There isn’t the same gulf, really, between a gibbon and a baboon, or even between a human and a spidermonkey.
Finch, AFAIC, the OP question was definitively answered a ways back. The thread is in free discourse time now.
I grant your points about the practical difficulty of rigorously refitting a Linnaean-derived ranking system to a modern cladistic understanding, but I’m not convinced that the impulse is useless or should be abandoned.
The rank of the taxon tells you the relative position of the corresponding node on the cladogram. It’s another way to represent that information, perhaps if one isn’t already familiar with their place in the hierarchy, that doesn’t require scanning a huge cladogram.
But the point would not be to suggest the diversity within each taxon, but to show the relative position of each in the diversity of the whole.
A phylum with a single species would be telling a story indeed! This distant cousin who broke away so long ago, yet has endured on its solitary path!
No, it’s not, because “systematic” has a definition that is much broader than the particular one you are using.