Here's why:

* Mammals are a class of animals. This means they share a set of defining characteristics.

* Humans possess all the characteristics of mammals:

* Give birth to live young: Humans don't lay eggs.

* Nurse their young with mammary glands: Humans have mammary glands (breasts) and produce milk to feed their babies.

* Have hair or fur: Humans have hair on their bodies, though it may be very fine in some areas.

* Warm-blooded: Humans maintain a constant body temperature, regardless of the environment.

* Breathe air: Humans have lungs and breathe air.

Therefore, humans are classified as mammals.