Ghost is like spirits.
When we say "ghost", we're thinking about a human spirit - after death.
So what makes us human beings special, that we have these spirits/ghost when we die?
Dinosaurs died long time ago, if such spirituality and paranormal "ghost" idea exist, don't dinosaurs have spirits too? Don't they become "ghost" too?
I just want to say that we're self-centered human beings.
We're living organisms just like any other: seal, lizard, frog, whatever.
I like to think of it in the big picture.