Final answer:
The main difference between Homo erectus and Homo habilis is that Homo erectus was fully adapted to upright walking with a body more similar to modern humans, had a larger brain, and was capable of using more sophisticated tools and possibly communicating vocally.
Step-by-step explanation:
One main difference Homo erectus had from Homo habilis is that Homo erectus walked entirely on the ground in an upright position and had a body adapted to this locomotion, whereas Homo habilis likely did not exclusively walk upright and still retained some primitive features. Homo erectus had longer legs, a broader pelvis, and arched feet, which were more efficient for bipedal locomotion, similar to modern humans.
Homo habilis, known as "Handy Man," had a smaller brain and more primitive body structure, with a jaw that was less prognathic than Australopithecus but still featured long arms. In contrast, Homo erectus had a larger brain, ranging from 550 cc to about 1,250 cc, and its body was similar in height to modern humans, with the capacity for endurance running, which was a new adaptation at the time.
Additionally, Homo erectus used more sophisticated stone tools, likely had some capacity for vocal communication, and showed evidence of caring for their community members, which are all traits that exhibit their more advanced development compared with Homo habilis.