Final answer:
The first species identified within the genus Homo is Homo habilis, which lived from about 2.5 to 1.4 million years ago and was ancestral to other Homo species such as Homo erectus.
Step-by-step explanation:
The first species identified within the genus Homo is Homo habilis. This species lived approximately 2.5 to 1.4 million years ago in East Africa. H. habilis is notable for its larger brain and the use of stone tools, and is therefore often dubbed 'handy man.' It was probably ancestral to Homo erectus, which in terms of its evolutionary timeline, appeared after H. habilis. Characteristics that could be used to define species within the genus Homo include a larger brain size relative to body size, reduced jaw projection, and changes in the bones and thumb positioning that indicate the capability for making and using tools.
Among the species that evolved after H. habilis, Homo erectus emerged about 1.9 million years ago and eventually became the probable ancestor to Homo heidelbergensis. Understanding the earliest species within the homo line helps us trace the complex and diverse evolutionary history that eventually led to modern Homo sapiens.