Why do all mammals share unique traits?

All mammals share unique traits due to their common ancestry, which dates back to a specific group of early amniotes. These traits, such as mammary glands, fur or hair, and three middle ear bones, evolved as adaptations to their environments and reproductive strategies. Over time, these characteristics became defining features of the class Mammalia, allowing mammals to thrive in diverse habitats. The genetic and evolutionary connections among mammals ensure that these traits are inherited and maintained across species.