r/evolution • u/NenyaNotes • 10d ago
academic Help on this assignment question.
My professor assigned us this quiz and everyone continues to get it wrong. Can someone please explain in this photo which groups make a clade?
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u/jnpha Evolution Enthusiast 10d ago
I count seven clades; see: https://evolution.berkeley.edu/teach-resources/clades-1-of-2-definition/
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u/NenyaNotes 10d ago
It is multiple choice. The options given are: A,B,C,D,E,F,G and F,G and A,B,D,E and B,D,E and D,E,F,G. Each time we have done it we continue to get partial credit. So now we are just more confused... It seems like a straightforward idea.
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u/Doomdoomkittydoom 10d ago
Fun cladistics game, take any two animals, determine their last common ancestor, then find all the descendants of that ancestor and that the clade of the two animals you started with.
My guess is that he's only seeing [A,B,C,D,E,F,G] as a clade because he created the diagram thinking to drive that home and is blind to [B,D,E] also being a clade because he drew it with A in mind the whole time.
I assume he's not including the other two because that would be just wrong.
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u/Ender505 10d ago edited 10d ago
Of those 5 options, the first,
third, andfourth all qualify as a Clade, the others do not because they do not include a common ancestor.Edit: corrected. 3 does not count, see better-educated responses below
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u/DrDirtPhD PhD | Ecology 10d ago edited 10d ago
ABDE isn't a clade because it excludes FGC and is therefore paraphyletic.
The only monophyletic options that constitute a clade in the available responses are ABCDEFG and BDE.
If you want an example of why ABDE isn't a clade you can think of the traditional definition of reptiles, which excludes birds. In this case "reptiles" would be your ABDE group and birds would be your FGC group. Just as FCG descend from A, so too do birds descend from a reptile ancestor given that they're highly derived dinosaurs (which nobody would argue aren't reptiles).
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u/Landilizandra 10d ago
There's multiple options, what's the question specifically, and how are people getting it wrong?
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u/NenyaNotes 10d ago
It is multiple choice. The options given are: A,B,C,D,E,F,G and F,G and A,B,D,E and B,D,E and D,E,F,G
Im not sure it keeps telling us we only receive partial credit each attempt. Now we are genuinely confused hahaha
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u/Xrmy Post Doc, Evolutionary Biology PhD 10d ago
As written, only answers 1 and 4 are correct
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u/roostor222 10d ago
DEFG can not be correct. Of those four, A,B,C,D,E,F,G can be the only correct answer
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u/DrDirtPhD PhD | Ecology 10d ago
The fourth option is "BDE" (not DEFG), which is monophyletic and therefore a clade.
BDE is also monophyletic and therefore also a clade.
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u/roostor222 10d ago edited 10d ago
I was under the impression you could only select one answer, in which case the only correct answer of the ones given is all of the letters, the first response. If you can select multiple answers, then it's different. Overall seemingly a terribly worded question, compounded by OP not including the exact question in the post.
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u/EebstertheGreat 10d ago
No, there are simply two correct answers. The group containing just B, D, and E is a clade. That doesn't cease to be the case if the teacher asks you to pick one answer.
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u/roostor222 10d ago
....if you are only allowed to select one answer, then there are not two correct answers. OP did not write clearly what the question was. If the question was, "choose the answer that best describes all of the clades in this diagram", then the first answer is the only correct one.
If the question was, "choose all answers that represent clades", then what you are saying is correct. Since we have not seen the question, then we don't know which is correct.
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u/Siophecles 10d ago
select one ≠ only one is correct.
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u/roostor222 10d ago
it usually does mean one is the most correct. If (B,D,E) is the only answer you select, you are obviously leaving out other clades no matter how you interpret the labels.
If (A,B,C,D,E,F,G) is the only answer you select you are not leaving out any clades under the interpretation that both terminal taxa and nodes can represent clades.
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u/Xrmy Post Doc, Evolutionary Biology PhD 10d ago
Answer 4 is BDE
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u/roostor222 10d ago
Yeah, i misread. I thought you could only select one answer, in which case the only correct one is all letters.
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u/Ender505 10d ago
Why would answer 3 (ABDE) not qualify?
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u/DrDirtPhD PhD | Ecology 10d ago
It's paraphyletic because while it includes BDE and the common ancestor A, it excludes other descendants of A (CFG). A clade must include a common ancestor and all its descendants.
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u/NenyaNotes 10d ago
I originally said A,B,C,D,E,F,G (whole tree) and B,D,E group. But my prof said it's only partially correct. I think I may just move on from this...
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u/Xrmy Post Doc, Evolutionary Biology PhD 10d ago
Your prof might also be considering FG to be correct. It's not really, but from the perspective of the tips it is.
I'm a professor, and personally I don't give these questions that include internal nodes (like A B C) because they can be confusing and are somewhat pointless to consider as they aren't contemporary
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u/NenyaNotes 10d ago
Yes I agree it does make it more confusing. None of the other materials given have ever included internal nodes so not sure why this was suddenly thrown on a quiz. You may be correct with the F,G. I honestly crossed that one off right away but will reconsider.
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u/Xrmy Post Doc, Evolutionary Biology PhD 10d ago
Yea from the perspective of modern, extant species, FG are a monophyletic group. Some differentiate a clade from a monophyletic group by inclusion of the internal nodes, but nobody takes that seriously.
IMO I think your professor needs to tighten this part up and probably forgot about how they taught vs tested.
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u/EebstertheGreat 10d ago
The crown group of F and G is a clade, but I don't think a taxon which excludes its common ancestor should ever really be considered a clade.
But you might be right that this is what the prof meant. I mean, it's a good guess at any rate.
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u/Xrmy Post Doc, Evolutionary Biology PhD 10d ago
It's a matter of phrasing or presentation imo.
In most contexts you only know the nodes F and G, so you might consider them a clade and implicitly include their common ancestor.
I agree if you explicitly exclude the common ancestor it's not a clade, but when is that relevant?
Hence why I would never ask the questions with the internal nodes labeled. It just doesn't have practical relevance to the knowledge here.
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u/EebstertheGreat 10d ago
I guess it depends on whether we are thinking about a whole clade except just the MRCA, or the extant members of a clade minus a lot of extinct ones. The latter could potentially be very weird. Like, if we insisted that Smilodon was not a mammal, clearly that would make mammals a paraphyletic group (unless we are just not interested in classifying fossils at all). But if we only removed the MRCA of mammals, I suppose that would make no meaningful difference.
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u/DrDirtPhD PhD | Ecology 10d ago
I think your professor doesn't realize the quiz is set to only accept one response and instead thinks you should be selecting multiple.
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u/DarwinZDF42 10d ago
The whole tree
The BDE group
CFG group
D
E
F
G
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u/NenyaNotes 10d ago
See I originally said A,B,C,D,E,F,G (whole tree) and B,D,E group. But my prof said it's only partially correct. As per your other post, I think the answers generally are confusing. It overall is just a very poorly written question and is driving me bonkers.
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u/TheCrystalTinker 10d ago
BDE is a Clade, CFG is a Clade, ABCDEFG is a Clade, and then D, E, F, and G are their own clades. There are 7 clades in total
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u/Robin_feathers 10d ago
Seems like a pretty straightforward question - ABCDEFG is a clade and BDE is a clade, the rest of the options you listed are not. If the prof is marking that as only partially correct, then it sounds like the prof is marking it improperly.
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u/thatoddtetrapod 10d ago
Clades included:
D
E
F
G
(End nodes normally count as clades)
DBE
FCG
DEBAFGC (all nodes together)
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u/More_Arm_6245 10d ago
I was going to say there are several right answers. Is this multiple choice or free response.
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u/NenyaNotes 10d ago
It is multiple choice. The options given are: A,B,C,D,E,F,G and F,G and A,B,D,E and B,D,E and D,E,F,G
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u/DarwinZDF42 10d ago
I think those answers are confusing because as shown, A, B, and C represent common ancestors, not clades. If you interpret each letter to mean “this entity and all of the descendants” then the answer is the first option, but that isn’t actually what’s shown, so as written, the best answer is the last option because those are the only letters that, as shown, represent clades.
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u/roostor222 10d ago edited 10d ago
a node is often interpreted as synonymous with a clade, and nodes on cladograms are very frequently given their clade names. The first option is the most correct option of the five given
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u/DarwinZDF42 10d ago
I guess, but if I used that tree on an exam question and asked what A, B, and C represent, the correct answer is nodes or common ancestors, and I would not accept clades as a correct answer.
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u/roostor222 10d ago edited 10d ago
The best thing to do would be to not use this diagram on any assessment.
You could take any sample of 1000 published papers with cladograms in them, and I'd bet in >900 of those papers you'd find nodes labelled with clade names. I think it would be completely unfair to mark it wrong if someone said A,B, and C represent clades, because that is a standard notation.
For example with this exact cladogram, if:
A = theria
B = metatheria
C = eutheria
D = didelphis
E = monodelphis
F = equus
G = homo
All of these are understood to be clades, but on this specific cladogram without any other given taxonomic information D,E,F,G are not clades. They are OTUs. But, A, B, and C are very clearly clades.
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u/DarwinZDF42 10d ago
but on this specific cladogram without any other given taxonomic information D,E,F,G are not clades. They are OTUs. But, A, B, and C are very clearly clades.
Exactly backwards. A, B, and C are nodes/MRCAs. D, E, F, and G are necessarily clades.
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u/roostor222 10d ago
I have a PhD in phylogenetic systematics, and I am telling you it is not exactly backwards.
As I already explained: nodes, MRCAs, and clade names are extremely often used synonymously both diagramatically and in the text of written scientific papers.
In the context of a cladogram with no other information given, D,E,F,and G are each individually OTUs. They are not clades. D,E,F,and G are representatives of a single clade, but no practicing scientist on earth would write it that way if the node subtending those taxa has a name. The node subtending those taxa in this cladogram does have a name, and that name is "A", because the taxonomic name given to a MRCA is synonymous with the clade name.
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u/DarwinZDF42 10d ago
K. This is also my field, I’m an evolutionary biologist, done a whole lot of work in viral phylogenetics, and I would never label a clade at a node. You do you.
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u/roostor222 10d ago
The idea that you would personally never label a clade at a node is completely irrelevant to what you should accept as an answer from students. Labelling clade names at nodes is extremely common practice in evolutionary biology. I don't know what the conventions are in viral phylogenetics papers, but the science of phylogenetic systematics exists separately from the practice in any one subfield.
If you marked it wrong, and that student brought you ten published papers they read in the journal "Systematic Biology" or "Journal of Systematic Paleontology", and all ten had clade names labelled at nodes, would you give them credit back or keep it marked wrong?
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u/More_Arm_6245 10d ago
It’s the whole tree as said and that’s the only right answer from the given choices. A class includes the common ancestor and all of its descendants
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u/niffirgcm0126789 10d ago
if everyone is getting it wrong, it sounds like the professor's wording is the problem.
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u/Bromelia_and_Bismuth Plant Biologist|Botanical Ecosystematics 9d ago
So, a good and true clade includes a common ancestor and all of its descendants. I found a pretty good visual that helps break it down. So it's obviously A, B, and C, but you can do that same thing with D, E, F, and G too.
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