Here's why:

* Domain: The highest level of classification, grouping organisms based on fundamental cellular differences. There are three domains: Bacteria, Archaea, and Eukarya.

* Kingdom: A large group of organisms that share common characteristics (e.g., plants, animals, fungi).

* Phylum: A group of closely related classes (e.g., chordates, arthropods).

* Class: A group of closely related orders (e.g., mammals, reptiles).

* Order: A group of closely related families (e.g., primates, carnivores).

* Family: A group of closely related genera (e.g., Canidae, Felidae).

* Genus: A group of closely related species (e.g., *Canis*, *Felis*).

* Species: A group of organisms that can interbreed and produce fertile offspring.

As you move down the hierarchy, the groups become more specific and contain fewer organisms.