==Logical evidence that Deckard is human==

Replicants are created for a purpose, and since they have a limited lifespan, replicants have limited time to "switch careers". Thus, IF Deckard is a replicant, he must have been created TO BE a hunter and deactivator of illegal replicants. The fact that he is physically inferior to the replicants he's supposed to apprehend makes no sense.
Thus, it only follows logically that Deckard cannot be a replicant.