This is in support of/response/addition to a Facebook post, where I asked if chickens can fly or not. It's not black and white as it depends on definitions, but it’s a great example of an inherited trait being lost or artificially designed, under our noses. At what point is a species classed as having or not having trait/attribute y?
On our Explorer, the clade nodes are visually represented by whether they are extinct or not, by way of the extinct symbol. In the past, some volunteer enthusiasts had not fully understood some of the rules of annotating cladograms, and resulted in us having to go back and re-check this error, which is ongoing but in hand. This was a learning curve, and taught us to ensure that we produce proper documentation, training, QC, designated roles and appropriately qualified or experienced personnel to monitor this.
The rule is, on extinction, (as a negative) that only if every example within that clade, fits, can the whole clade be annotated as such.
So, dinosaurs (because birds form a part of this clade) must be left open as being extant, NOT just the bird part. And further, ALL clades higher, that encompass dinosaurs, must also be left open as extant, right back to the root. Only the subordinate clades which have no examples remaining, can be annotated at its root node. There are no other examples of dinosaurs left, so if all birds died out tomorrow, dinosaurs could be said to be, and annotated, extinct. The term, ‘Dinosaur’ is being used in the cladistics sense.
But, if we were to apply the positive attribute of flight (true flight – unassisted by gravity, wind or other body or external source) to chickens, then if any, single example still flies, it (the clade root) does not get a tick unless all fly. The same logic/implication would mean that flight needs to be ticked in all higher clades back to the root, but clearly, flight had not evolved then. So, what happens, is at the onset of flight, flight can be ticked. Flight is not a cladistics term, it is/can be, a part of what makes up the collective defining attributes. So, whilst all descendants of birds, remain birds (and also whatever new clades/derivatives they evolve into), flight is something that can change. So, any bird which cannot fly, can be ticked as a non-flier, individually, but to compare extinct, flight and other things is not entirely fair comparables.
I would be inclined to say that chickens can fly, only IF there is a verified, extant example and we may need to ask about whether wild and domestic ones are included or how far back we go. The internet seems to show that there are examples, under the limits I presented above, (but many dubious ones, too, with nothing that has yet convinced me, but feel free to post/link), but I’d like to see more concrete evidence.
Perhaps surprisingly, I have never seen evidence that a hippo (the, ‘river’ horse!) can actually swim, despite some extensive searching and videos, from zoos and in the wild. But swimming may need defining.
I would also point out that the record distance for a chicken flying, is under 100m. Flying fish can travel much further and for much longer, through the air by distance. How does 45 seconds, horizontally sound! Is this potentially flight? So just bear that in mind, and, like my own discovery and photographic evidence of a new species of highly venomous snake, photo’s may not tell the whole story or provide enough evidence, (see the blog on the Website entitled, ‘The sacrosanct nature of verification’ or note what, ‘Trigger’ would like you to think in this attached video, that he shows proof. And there is a philosophical reflection of, ‘the ship of Theseus’ problem which you may like to search for. It’s always good to learn something new, especially if you’ve done ten impossible things before breakfast.