Lock and Key Mechanisms and the Labyrinth in Small

The lock is a physical emblem of the historical development of social distrust. And i think this is probably a problem that arises only once you reach a point in history where there are large tlements in which the inhabitants don't all know each other well. Once humans are living a settled existence in one place, gaining wealth based on agriculture, and forming conglomerations of humans containing persons of unknown trustworthiness, you can imagine a desire for something like a locking mechanism just being a natural consequence as they increase in social complexity.