There were humans inhabiting Europe prior to 400, 000 years ago. The humans who first mastered fire used it for heat but not for cooking. The climate in Europe was significantly colder 400, 000 years ago than it is today. Humans would not have mastered fire were it not for the need for heat in a cold climate.
Archaeologist: The earliest evidence of controlled fire use in Europe dates to just 400, 000 years ago. This casts doubt on the commonly held view that, because of Europe' s cold winter climate, mastery of fire was a necessary prerequisite for humans' migration there.
Which one of the following is an assumption required by the argument?