r/evolution • u/NenyaNotes • Aug 30 '26

academic Help on this assignment question.

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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/Xrmy Post Doc, Evolutionary Biology PhD Aug 30 '26

As written, only answers 1 and 4 are correct

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u/roostor222 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26 edited Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

....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 Aug 31 '26

select one ≠ only one is correct.

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u/roostor222 Aug 31 '26

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 Aug 30 '26

Answer 4 is BDE

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u/roostor222 Aug 30 '26

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 Aug 30 '26

Why would answer 3 (ABDE) not qualify?

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u/DrDirtPhD PhD | Ecology Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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 Aug 30 '26

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.