Here's why:

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

* Hair: While humans have less body hair than many other mammals, we still have hair.

* Give birth to live young: Humans do not lay eggs.

* Mammary glands: Human females produce milk to nourish their offspring.

* Other characteristics: Humans share many other characteristics with mammals, such as a four-chambered heart, a muscular diaphragm for breathing, and a relatively large brain.

Therefore, humans are classified as mammals within the animal kingdom.