I recently registered for ChristianForums.com, and this thread caught my attention, because I'm, like, a Vegan (go animals!).
I'll just say what I have to say real quick:
There was 17th Century Philosophy by the name René Descartes (you may have heard of him, or perhaps his famous statement "I think, therefore I am"). Descarte was an Ontological Dualist, meaning he believed the human mind (or innate consciousness) was substance which existed seperately from matter. He went as far to say that humans do in fact have a soul.
However, he developed his Cartesian System. In doing that, he makes a statement that almost makes me wonder: He professes that no non-human animals have a soul (he said this around the time of 1640).
Descarte argued that because animals have no souls, they cannot think, feel emotion, of
feel pain. *cringe*
Descarte believe it was man's Devine obligation to be the rulers of Nature. To do this, he believed Physiology was the basis mechanics (a name he used for "medicine"). In his study to increase his knowledge of mechanics, he took live animals, then he vivisected them to see their moving inner-parts.
When it was noted that animals he was vivisecting were clearly in pain, Descarte responded by saying the animals were merely programmed to behave as if they were really feeling pain. *cringe again*
Enough of Descarte... (Oh one more thing: While he was the father of Modern Philosophy, most of his metaphysics - i.e. the ones about animals and pain - are rejected.)
Here is some information on other animals...
Insects: Insects have what biologists called a "Cerebral Ganglion" and "Neural Net". While insects (as well as the rest of the Arthropod Phylum) have no central nervous system, their Neural Net is about as close as they can get to one. Insects lack the proper structures that would allow them to feel pain, in fact insects have no cognitive abilities at all. While they cant feel pain, its still not nice to kill them. The reason why biologists speculate that they dont feel pain is due to the fact that they dont behave in a manner that would be construed as symptoms of pain (although it isnt known with 100% certainty, a few telltale signs such as losing a limb without noticing its gone insinuates that the critters cant feel pain). While they will run away if something is trying to eat them, that is not a definite sign that insects feel pain, its just a life-preserving mechanism (again, that's not a definite sign that the insects value their own lives or well-being). Most biologists think of insects as little minature machines which behave in pre-programmed ways, there are a lot of experiments (which are humane by the way) to support this view.
Mammals: Yes, mammals do share a few common characteristics. One of which is the ability to feel pain. Regardless of having a soul, all mammals (assuming their brains have developed the proper structures) are able to feel pain. Whether or not all mammals are self-aware is a different story (we know Orangutans and Chimpanzees are self-aware by the way they respond to mirrors, however Gorillas respond to mirrors in a way that it seems they dont know that they are looking at themselves).
Fish, Reptiles, and Amphibians: The brains of Fish, Reptiles, and Amphibians are actually remarkably similar. It is believed that these animals can feel pain, although they have very primitive brains. The reason why is because pain is a low-level brain function, its not the same as high-level brain functions such as cognition and strategizing. Jellyfish on the otherhand are not of the same Order, they do not have a centralized nervous system, however they do have a neural net and glanglion tissue, its not thought that Jellyfish feel pain.
Plants: They dont feel pain.
I hope this post has been helpful
Yeah! First post!