Hell, I can't even tell that you 'feel' anything. I only know that I 'feel' because I am able to subjectively experience it. I make the assumption that you feel because you appear to be very much like me in all other respects, however there is no objective measurement that can prove or disprove that assumption. Historically, not every culture even gave all human beings the benefit of the doubt on that, let alone animals (which contemporary western cultures at least often agree do 'feel').
Where you draw the line is seemingly arbitrary. Some might say that means there isn't one, that either we're all P-zombies (or at least everyone who isn't me is), or we live in a panpsychic universe. Of course, the universe has often resisted such black and white categorizations.
Consider this then: why do we care? I submit that the only reason we care whether or not something 'feels' is so we can exploit it without guilt, so we can shield our empathy from the consequences of our actions. I feel it is important to keep this in mind when making decisions which hinge on questions like whether or not something can truly 'feel'.
I get that your point is much broader; the meaning of "feeling" is going to keep staring you in the face when thinking about a question like this, but it's a sophomoric question to anyone who accepts the possibility of it's discovery without a metaphysical understanding of a sunflower's conscious experience.
Philosophically, yeah. But if you can't prove or disprove anything, then "proving" isn't a useful metric. Being the same species should give you confidence that the grandparent is capable of feeling. (I'm assuming in best faith the commenter isn't a bot)
Even in the most ideal circumstances we kill other beings simply due to resource consumption. Maybe not now, but in the future - what we consume isn't available to them. Even if you claim the resources we consume aren't food to the food species of your choice, due to the law of increasing entropy we definitely shorten the lifetime of whatever comes after us just by existing.
Hardcore buddhists for example consider all life equally worthy. No karma bonus for vegans, maybe less than for non-vegetarians who buy only from farms which provide a healthy, livable life to the livestock (or, obviously, for the plants)
Some have already abandoned that idea. I quote Joseph Campbell[1]:
"Life lives on life. This is the sense of the symbol of the Ouroboros, the serpent biting its tail. Everything that lives lives on the death of something else."
https://www.amazon.com/dp/1771642483/
It suggests that trees may have some kind of hive intelligence in their roots and through the fungal networks they can communicate and share resources. It isn't something that I've investigated in a ton of detail but the ideas seem scientifically informed.
https://www.amazon.com/Thus-Spoke-Plant-Groundbreaking-Disco...
It describes some experiments which can be interpreted as plants "remembering" and "predicting" things.
Here's a recording of a (~1 hour) presentation I saw her give: https://www.youtube.com/watch?v=SZFKon7kook
I don't know what to make of this, but it's certainly made me think differently...
The answer probably lies somewhere in the middle. Rather than viewing trees as a hive intelligence, I think it’s plausible that we’ve been missing the forest as a whole organism. Perhaps “ecosystem” just means “an organism that is bigger than any one of us.”
I don't know of any way to prove feeling. It seems like a solipsistic trap. I _believe_ that most animals "feel", and _believe_ that no plants/fungus do...but it is merely belief that I don't think to be testable.
We can start out with the assumption that humans can feel, since ourselves experience it, and can relatively safely transfer this to other humans (who exhibit all the subjective external signs of feeling, which seem similar to our own external signs when we are feeling things). We can also isolate the physiological properties which seem to play a role in this; say, a nervous system, or particular brain characteristics or region activations. This can be further evidenced by cases where individuals lack these, and lack the external signs of the feeling.
So if you then take a physiologically highly related and similar animal to a human, which also shows the external signs of feeling, I believe the argument that it is NOT feeling would be the option that is more absurd, and requires more proof than the argument that says it is feeling.
Of course, this rapidly falls away when we argue about very different types of creatures (say, fungi), or when theorising about types of feeling that might be possible, but we do not have, but nevertheless the entire topic is not worthless, IMHO.
Additionally, although oysters (and at least dozens of other species of animals) lack a CNS, they also react to external stimuli. In fact, oysters are used in some water systems as sophisticated water quality detectors, e.g. in San Diego https://www.youtube.com/watch?v=UJJz15N1KEY .