Homo erectus/ergaster
Paper instructions:

Homo erectus/ergaster was the first hominin to really look much like us modern humans and to have all the same basic body proportions, which means they would have the same basic big game hunting abilities and have the ability to cover long distances in hot, dry environments. They were also the first hominin to have a more mobile tool kit (the Acheulian hand axe) that could be more easily carried from place to place. This hominin appeared right around the time that grasslands were rapidly expanding throughout Africa and between Africa and Eurasia: grasslands that support many more animals than forests can. Based on all this can you suggest a scenario explaining the evolutionary emergence and spread of Homo erectus/ergaster from their East African place of origin?