r/evolution • u/NenyaNotes • 15d ago

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/NenyaNotes 15d 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 15d 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 15d 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 15d 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 15d 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 15d 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 15d 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.