Because humans have eternal souls and others don't?

• Well, the soul is not scientifically proven. It has neither been found in animals nor in humans.
• Evolution, the idea that all things in this universe came into existence through stepwise development, does not accommodate an eternal soul.

Because humans have consciousness and others don't?

• What is consciousness? It is a subjective experience: desires, needs, emotions, feelings, and the sense of "I" in the mind.
  Studying and researching the brain reveals that stimuli act as input, neurons fire to make decisions, and organs (via motor neurons) perform actions/output. This process can occur autonomously, like an algorithm. My senses receive input, my brain (neurons firing) makes decisions, and my organs act. All of this can happen without the need for consciousness.
  Why did we develop consciousness? Perhaps it evolved to increase survival rates by enabling communication and interaction with other members of a group.
  Consciousness is real and plays an important role in ethics and politics. It is a biologically useless by-product of certain brain processes, yet our entire society is built upon it.
  However, consciousness is not limited to humans; animals also possess consciousness.
  How do we test for consciousness? We observe brain signals when a human reports being conscious, then use that data during diagnosis to check for consciousness. We look for similar patterns in the brain, relying on correlation rather than causation.