What is the MOST specific classification that humans and tigers have in common?

The most specific classification that humans and tigers have in common is Class Mammalia.

Here's why:

* Kingdom: Both humans and tigers belong to the Kingdom Animalia.

* Phylum: They both belong to the Phylum Chordata (having a backbone).

* Class: They both belong to the Class Mammalia (having mammary glands, fur/hair, and give birth to live young).

* Order: They belong to different Orders - Primates (humans) and Carnivora (tigers).

Therefore, Class Mammalia is the most specific classification they share.