Answer in complete sentence pls!:) (Mammals)
Mammals are living creatures that all have several characteristics in common. First, all mammals have hair. Some have thick hair, while others have thin and wispy hair. Mammals also give birth to live young; their babies do not hatch from eggs. All mammals also have four limbs. Some walk on all fours, but others can walk upright. Mammals also use lungs to breath and have vertebrae that make up a backbone. Some mammals, like whales and dolphins live in the water, but need to come to the surface for air. Mammals can be found all over the world, on every continent. People are mammals, too!  

What is the author’s purpose for writing this paragraph?​