Not a biologist here as you will propably be able to tell.
I understand that throughout the tree of life each species at the leaves at the same time also belongs to all the parent categories up the tree. So humans are apes and also are primates. The most frequent use of that fact in everyday discussion is in reply to the question "if humans evolved from apes, why are there still apes?". I also get why that question is silly.
I wonder, however, how biology would treat future evolution.
Assume that 10 million years from now our descendants are still around and have developed some trait that conflicts with the current distinction defining the branching of the taxonomic tree. Let them for instance grow some sort of tail again. Possibly to keep their hands free while still clutching some mobile device (I believe taillessness is one of the characteristics differentiating apes from other primates, if I am wrong about that please just substitute any trait that is).
Also assume that todays' other primates and apes are still around in that future.
Would we still say "homo futurensis are apes", even though they have tails?
Or would future taxonomists rearrange the tree and restate the distinctions? If so would that imply that looking back from that future to today us currently tailless humans would also not be apes after all but on a different branch together with h.futurensis? Is there a time-dimension to the layout of the tree of life? I don't mean corrections as we learn more. But changes due to evolution taking its course. The appearance of a new species forcing a remap.
Or would we just keep the tree and drop the tail-thing from the list of characteristics because there are enough other things that define the commonality? If so we could imagine even further evolution changing those traits too. What then?
Or does the new tail not pose a conflict in the first place because it would be something new. "Tail" being a naive name and the new appendage propably being called something else?
Or is the question plain silly, if so please explain why.