As you get older, your sense of justice and morality will be questioned far more than it ever was as a child. As a child, you might want to keep things to yourself, but as a grown-up, that's pretty selfish. Eventually, no matter how hard it is, you've got to accept that you need to share your food from time to time - no matter how tasty it is.
This only applies to humans, however, as other animals aren't too bothered about being so polite. Even animals whose DNA isn't too far off ours won't do the same. Try getting a monkey to share its food with you - it's not going to work. In fact, they're more likely to keep you far away just in case you steal their grub.
In this footage, filmed inside a zoo in China, one monkey was so defensive over its food it straight up punched a little girl in the face. Some have said that she was taunting him, but the girl may have been only crouching down, watching her accompanying adult feed the animal. Regardless, this was enough of a risk for her to get a bop to the face.
This is just plain rude in our world, but I imagine for other primates it's a different matter. Getting a left hook to the cheek for staring at a mate's food for too long isn't something that goes down too well in the animal kingdom, it seems.
However, I think if you pulled this at the family dinner table it wouldn't be quite as acceptable.
