Mammals are the most diverse species on Earth. It is vital to understanding the origin of mammals by using fossil records as evidence. Fossil records that are recently discovered hold a significant information regarding the origin of mammals. Mammals have different sizes, forms and shapes. These varieties help mammals to demonstrate adaptive behavior in order to survive the environmental and habitat changes. All mammals are interacting with each other. Human, as a species of mammal, domesticates other species. The domestication may impact the intelligence strategy of some mammals. The domestication requires studying the behavior of species related to the physical structure, such as migratory behavior, communication behavior, and sexual behavior. The reproductive system in mammal differs from other species. Mammals have several reproductive strategies that are aligned with the changes in environment and habitat