Human evolution refers to the long-term process of biological change observed in the lineage leading to modern humans. Key adaptive transitions throughout this period include the development of bipedalism, which freed the hands and was crucial for terrestrial locomotion. Subsequent evolutionary changes involved the expansion of the braincase and the refinement of complex behaviors, such as the manufacture and systematic use of tools. Dietary shifts, moving towards more varied and energy-dense foods, played a significant role in fueling the metabolic demands of a more robust brain. This overall progression is understood through the fossil record and comparative anatomy, demonstrating adaptations to changing environments over millions of years.