Scientists analyzed and studied the fourth metatarsal bone of the foot bone of Australopithecus Australopithecus excavated in Hadar site, Ethiopia, and found that Australopithecus Australopithecus Africa has a stereotyped arched foot  According to this, they believe that human ancestors began to walk on both feet like modern people as early as 3
Only when you walk with both feet can you have a stereotyped arched foot
2 million years ago