Large stone-cutting tools dubbed hand axes regularly appear at prehistoric archaeological sites from India westward across southern Asia into Europe and Africa. In 1944, Harvard anthropologist Hallam L. Movius Jr. proposed that those prehistoric populations, living 1.6 million to 200,000 years ago, existed on one side of a geographical line that separated them from groups in central and eastern Asia, where early humans fashioned much simpler stone implements.

Now, the discovery of ancient