It seems that humanity is slowly moving towards the collective realization that animals of other species have moral worth – that they are not objects to be treated however we wish. There’s still a long way to go. We may talk the talk, but as long as things like factory farming exist, those words look pretty empty.
It’s unsurprising that philosophers may be found at the forefront of the battle for animal rights, since their job is to question that which is taken for granted. Nevertheless, even philosophers have often reinforced the assumption that “humans” and “animals” are two strictly separated groups.
There are two basic meanings of the word “animal.” There’s one that makes perfect biological sense: “animal” is coextensive with the biological kingdom Animalia. Then there’s the other one, far more commonly used: “animal” means everything in the kingdom Animalia except for humans.
Whichever definition we use, there’s an enormous diversity of differences on every scale among animals. Each difference also tends to appear on a spectrum, so intelligence, for example, ranges from minimal to great through all the steps in between.
In spite of all this, there’s a tendency to make generalizations that leave humans on one side and all other animals on the other. These are not automatically false, since humans do have some unique features (or features that are farther along a spectrum than those of any other animal, as with some kinds of intelligence), but they should be made with caution instead of assuming they are a safe bet. Besides, there are probably other species that also have their own unique features, but we don’t put them on the same kind of pedestal.
Sometimes, when making generalizations about other animals, people will really be talking about humans. Say someone is writing an introduction to an anthropological text and wants to make a point about how it’s part of human nature to think about the past and look forward to the future. They might start this point by saying “Humans, unlike animals…”
Now, since thinking of the past and future is a trait related to high intelligence, it might well be true that humans are rare if not unique among animals to have this trait. But why does an anthropologist with no background in animal psychology potentially falsify their own claim about humans by bringing in other animals? We seem to use non-human animals as a negative mirror reflecting what we think of ourselves.
As far as moral value goes, there are two main schools of thought. One is that a thing has moral value as long as it has interests, is capable of pleasure and pain and so on; if something can be hurt, you shouldn’t hurt it. The other is that for your interests to count, you have to belong to some kind of an exclusive club, usually excluding non-human animals. I think drawing such lines between humans and animals is only a little less monstrous than drawing them between humans.