Homo erectus is a key member in the evolutionary history of early humans. Their fossils suggest they lived in Africa and Asia between 1.89 million and 143,000 years ago. Homo erectus is the first species of Homo with modern human-like body proportions, having longer legs, shorter arms, and relatively large brain cases. These features are considered adaptations for living primarily on the ground with the ability to walk and possibly run long distances. This likely led to this species being the first early human species to venture beyond Africa, into Asia. There is fossil evidence that this species cared for old and weak individuals, signaling the appearance of empathy and close social bonds within groups. The appearance of Homo erectus in the fossil record is often associated with the earliest hand axes, the first major innovation in stone tool technology.

Evolution occurs when a species adapts and changes over time through descent with modification. This is based on selective pressures within their environment. Human evolution is no different. Early humans walked on four legs, ate mostly plants, and had small brains. Over millions of years, they adapted to take advantage of the world around them. For example, they began to walk upright on two legs, became predators and skilled hunters, and developed large brains that allowed for sophisticated communication, a higher degree of forethought and planning, complex social interactions, and other traits that define them as a species. Often these adaptations were in response to a change in their environment, such as temperature change in the beginning or ending of an ice age or when a new species of predator moved into the area. Like all species, modern humans continue to change today and further adapt to their environment.

By studying human bones, physical and forensic anthropologists can learn a number of things about events of the past and the present, and the people who experienced them. The condition of bones, the location they are found in, and items they are found with can inform researchers about burial practices and the circumstances leading to disposal of the remains. The bones themselves can tell researchers how old a person was, how tall they may have been, if they were a man or a woman, and what role they played in their society. Information on diet and activities in life can be found in bones by looking at their composition. Researchers can also learn about diseases that leave marks in bones and how they affect individuals and populations through time. Bones can sometimes tell researchers how a person died and this information may help law enforcement agencies solve modern forensic cases.