A defining characteristic of mammals is the presence of mammary glands, which produce milk to nourish their young. This trait is pivotal for the survival and development of mammalian offspring. Additionally, mammals possess hair or fur, and most are warm-blooded, allowing them to regulate their body temperature. Mammals typically have complex brains relative to body size, contributing to their advanced behavioral capabilities. These characteristics, along with a unique structure of the inner ear and three middle ear bones, distinguish mammals from other vertebrates.