Time is the medium in which history and politics evolve, yet historians and political scientists have devoted limited efforts to understanding it. The familiar notion that time flows regularly, objectively and in a clear direction has severe limitations. Above all, it makes it difficult to understand the huge differences in perceptions of time in different cultural contexts. Norbert Elias argued that time, like money, can be understood as a social convention; it arises from the activity of "timing" or "scheduling". All living organisms have to align their actions to the rhythms of a real world, so natural selection has built into them the ability to detect and react to significant rhythms. Humans are unique because they relate to the world's rhythms in diverse ways, so different communities may experience time differently. Elias argued that as societies became larger and more complex, schedules became more inter-twined, creating the illusion of a single, unified temporal dimension. Meanwhile, the increasing pace of social change generated a growing awareness of time as history. These changes are the foundations for our distinctively modern sense of time.