Final answer:
The split between the chimpanzee and hominid line occurred around 6 million years ago. This event led to the evolution of hominins, which includes species like Australopithecus and Homo habilis, characterized by bipedalism and increased brain size. Sahelanthropus tchadensis is an example of an early hominin species that lived at the time of the divergence.
Step-by-step explanation:
Origins of the Hominin Lineage: The chimpanzee and hominid line split occurred approximately 6 million years ago. This crucial divergence marked the evolution of hominins, which are any human or human ancestor that evolved after this split. The definition of hominin thus refers to species that are more closely related to humans than to chimpanzees. Early examples of hominins include Australopithecus, Homo habilis, and Homo erectus, each showing traits such as bipedalism, increased brain size, and tool-making abilities. Sahelanthropus tchadensis, a fossil species thought to have lived right around the time of the split, further provides insight into this early epoch of human evolution. Understanding this timeframe is essential when discussing human evolution, placing our species within the broader context of the hominid family, which also includes the great apes. The genus Homo first arose approximately 2.8 million years ago, signifying a momentous phase in our lineage characterized by full bipedalism and relatively small brain sizes in comparison to modern humans.