It could be a soul. We humans have something more than all other animals. Sometimes it's for the better, and sometimes it's for the worse.
We are animals, but what more do we have that 'they' have none of?
If the soul wasn't invented as a device for preserving a person's innermost essence beyond the physical realm, then why can't it be defined as things that aren't based in the physical?... How do you define the soul?