Final answer:
The Australopithecines are believed to be the first species to walk upright, with Homo erectus being a key descendant that also walked upright. Homo habilis, known for its tool-making, is another significant predecessor in the human lineage.
Step-by-step explanation:
The first species that is believed to have walked upright is the Australopithecines. This genus of early hominins dates back to about 3.9 million years ago and includes several species.
One of the key descendants of Australopithecus was Homo erectus, which evolved from earlier species such as Homo habilis. The shift to an upright, bipedal lifestyle had significant evolutionary advantages. It allowed for the use of hands in tool-making and contributed to changes in diet and living environments. Homo habilis, which stood around 2.5 to 1.4 million years ago, is another significant figure in the human lineage and is referred to as the "handy man" due to its associated stone tools.
Our own species, Homo sapiens, evolved alongside these earlier hominids and eventually spread out of Africa to inhabit various parts of the world.