Gah, evidence. Well, I'm not at the computer I use in college right now, so I can't give you any sources right now, but take out books on animal and infant consciousness. Thats a good start.
Okay, as far as animal consciousness goes, I'll admit that the evidence is a little shaky. Human consciousness, less so.
A few things have led many philosophers and psychologists to conclude that infants do not have a concept of self until around age two.
1. They don't recognize themselves in the mirror until around age two.
2. At the same time they start recognizing themselves in the mirror, the way they talk about themselves and the world around them starts to change dramatically. They are more likely to talk about how they feel, they get better at distinguishing their actions and emotions from other's, stuff like that. This sort of development continues until age 7 or so, which is when a child's concept of self becomes fully developed. But the evidence for a rudimentary concept is there around the age of 2.
Animals:
Well, with animals, psychologists mainly rely on the mirror test. Basically, if the animal seems to recognize itself in the mirror, can use a mirror as a tool to inspect parts of its body, for example, it seems to follow that it might have a concept of self. A vast majority of animals fail this test; they either ignore the mirror, or treat it like some other animals.
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How do you know? How do I know that you have a concept of self?
behavior baby. I act like I have a concept of self; therfore its a good bet that I do. We've never met in real life, so thats all you really have to go on.
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Something someone said about cat's that rory doesnt remember and is too lazy to look up
I think you should take another look at your cat, because empirical studies have been conducted on a variety of animals, including cats, and have concluded that they DO NOT recognize themselves in the mirror. So, either your cat is the most wicked smart cat ever, you are mistaken, or the scientists are wrong.
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Completely absurd and the analogy is even worse.
Well, the analogy of the stage performing with no one there to see it is your classic Cartesian Theatre, except without the audience member. If you think of the concept of self as the "inner observer"(even though this is just sort of an illusion) that receives all perceptual phenomna (like vision, touch, etc) and initiates all conscious action (like running, jumping, turning ones head, speaking, etc), then the analogy works rather well.
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So to use your own anaology the experience of a baby would be more like the Opening of the Sydney Olympic games with a billion people watching it. Not this empty stage your referring to.
Wait, did I say empty stage? If I did, I sincerely apologise. No, the stage is full of people. People dancing, juggling, eating bears, etc. There's just no audience member, no inner self to see whats going on. Its like all this perceptual input is flying through the baby's head with no inner self to actually witness anything. I rather like the analogy...
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I remember things from when i was 2!!!
Well, first of all, that doesn't really go against what I'm saying. If anything, it rather fits with it. People develop a concept of self around the age of 2; your earliest memories are around the age of two... Secondly, memories are shaky things; they frequently change, and sometimes they are completely made up! For example, if I saw pictures from my 1st birthday, and my mother always described it in vivid detail, I might actually construct a memory of my 1st birthday, even though I was much to young to remember it. Theres a rather famous example of memory fabrication actually. It involves a women, a sledge hammer, a wall, and an angry (or not so angry) uncle. Long story short, some girl has a distinct memory of witnessing an event that she: A. never attended, and B. remembered "wrongly," that is the event happened for a completely different reason than she remembered.
With all that said, I think I should make it clear that I was a bit rash about my judgements about people and animals. I think the evidence is fairly convincing (though Im not entirely sold) that animals and infants under the age of two don't have a concept of self. Now, assuming they don't, I think you can agree that would be a big deal. If something doesn't have an "inner self," then whats going on in there head? I have trouble imagining it. Theres no "person" (though, as i sort of said before, the concept of self is sort of an illusion we have about how our minds work, anyway) inside to receive all that perceptual input! Its just flying about...
As a side note, Daniel Dennet argues that a concept of self developes at an early age (around two) due to social factors, and is especially enhanced by language.
I think an important thing to keep in mind when creating an ethical system is what can feel, and what it means to feel. A concept of self seems fundamentally linked to this topic.
When deciding whether or not its okay to eat meat, for example, we should consider what the cow experiences. Does it have a concept of self? Does it have any concept of the future? Does it have a desire that its future states are met? Does it feel in any way that can truly be called "feeling," as we define the term? If the answer to these questions is no, then perhaps it is okay to kill the cow and eat it. I think we should be open to that possibility.