This is part of something I posted in another thread but thought it might be more appopriate as its own...

Our basic presumption is that a human life is intrinsicaly worth more than a cow, a monkey, an elephant, or a blade of grass. I am no longer certain of this personally.

This does not mean a human life is worthless, or that I would just as soon kill a person as an ant. But i may admit that the only reason I feel more horror at the idea of a dead human is because I am human, not because there is anything more important about being a human (which is probably why so many people can justify slavery or killing those who appear different from them).
I think this basic discussion relates directly to our ideas and preconcieved notions of morality. How do you come to the decision that a human life is intrinsically worth more than another form of life--logically. And if you come to the conclusion, as I have, that it may not be worth more, does this change your notion of morality?