Homo Erectus, or "Upright Man" were the oldest of the known human species to possess similar features to modern humans. These features marked a period in time when humans began to leave the trees and live and explore on the ground. With the development of longer legs and shorter arms (in relationship to their torsos) Homo Erectus became more well suited to walking and even running much further distances than their previous, more ape-like ancestors "Homo habilis" (although there is evidence they and other human species coexisted).
Homo Erectus height varied widely from location to location, across the globe, with some skeletal remains estimated at up to 6 feet and others significantly shorter. Regardless, they were on average much taller than their ancestors. Their facial features also looked much more like modern human, with smaller teeth and a much more similar forehead. In regard to intelligence, Homo Erectus had a much larger brain than another of its ancestors, "Australopithecus", and therefore they required a much richer diet to feed their brains.
Beginning in Africa approximately 1.8 million years ago and living until possibly 50,000 years ago, Homo Erectus marked a major advancement in stone tool making. This period of time is known as the "Acheulean stone tool industry", and it began a time when humans created larger and much more sophisticated stone tools such as hand axes, scrappers and other cutting tools, in order to survive an ever changing climate.