Why are Humans the only race who kill their own kind?

I never got this, is it because we're not as smart or 'civil' as we like to believe? How can humans be so arrogant when animals are so much more empathetic and thoughtful for their own. If man is so smart, why are they always starting WARS?!
Update: I think people hosting here are blinded by their human arrogance, animals do *not* kill their own.
Update 2: I'm sick of people making up 'facts' just to think that humans are better than everyone else.
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