Final answer:
The hominin lineage took shape after splitting from a common ancestor with chimpanzees about 6 million years ago, evolving characteristics such as bipedalism and larger brain sizes. Species within this lineage, including Australopithecus and Homo erectus, contributed to the development of Homo sapiens, who have survived as the only extant human species.
Step-by-step explanation:
The formation of the hominin lineage is a complex aspect of human evolution that encompasses the divergent evolution of the human family after our common ancestors with chimpanzees and bonobos first went their separate evolutionary ways, about 6 million years ago. The hominin lineage includes our own species, Homo sapiens, as well as other species more closely related to us than to chimpanzees, such as the genus Australopithecus and Homo erectus. The term 'hominin' helps us reference those species that evolved after this split in the primate line.
Fossil evidence indicates that early hominins like Australopithecus already walked upright, showcasing the first evidence of bipedalism, which is a key marker of the hominin group. Over time, the genus Homo emerged, with species such as Homo habilis and Homo erectus demonstrating more traits similar to modern humans, such as increased brain size and the use of tools. Though many hominin species arose and died out, each contributed to the tapestry of human evolution.
The history of human evolution is continually revised with new fossil discoveries, advancing our understanding of how Homo sapiens emerged by about 300,000 years ago, equipped with advanced tools and mastery over fire. As these early humans migrated and interacted with their changing environment, they developed new subsistence strategies, further driving human evolution forward.