A historian argues that the caste system should not be viewed as a completely unchanged institution stretching back three thousand years. Which evidence would provide the strongest support for this argument?

The earliest known form of the system allowed movement between categories and was not strictly based on birth.

The correct answer is Option 3: The earliest known form of the system allowed movement between categories and was not strictly based on birth.

An institution cannot be considered unchanged if one of its most important characteristics has undergone a major transformation. The shift from a relatively flexible system to a rigid birth-based one demonstrates significant historical change rather than continuity.