Archeologists have discovered three sites showing conclusive evidence for the mastery of fire in Tanzania, from a period slightly after the time that Homo habilis was present in Africa. These sites clearly were founded by Homo erectus, the descendent species of Homo habilis that migrated north, out of Africa and into Asia. Homo erectus was known to have mastered fire, from ample evidence at sites in Asia. There is no reason to attribute mastery of fire to Homo ergaster, the descendent species of Homo habilis that remained in Africa.
Which of the following is an assumption on which the argument depends?