Anthropologist: During the last ice age, nomadic communities probably needed at least 15 or 20 members to survive, and they were generally not much larger than this.
Your task
Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.
Common trap
Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.
Winning move
Predict what a right answer must do, then test each choice against the conclusion-evidence gap.