Along with us (humans), there are over 5,000 types of mammal specieis. This includes birds and fish. Due to environmental changes, many of the species are becoming extinct. Mammals have many things in common.
One is that they all feed their young milk. When a human has a baby, the baby will be fed either breast milk or formula. All mammals have a mammary gland, which allows them to produce milk for their young. Another thing that all mammals have in common is that they all have hair and some have more than others.
