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[History and demographic systems].

Is it possible to describe the past evolution of populations by using the notion of system? This article shows that three obstacles arise: the disciplinary stricture, that is, the artificial isolation of demographic phenomena cut off from the political and economic phenomena on which they depend; the spatial stricture, that is, the delimitation of a given zone, quite often a village or small town, which means excluding readjustments, by migration; and, finally, the confusion of scales, that is, the passing from an individual level ("micro") to a collective one ("macro"). Given these obstacles, the few systems proposed are severely limited. An example of this limitation is given with the model called self-regulating, which is disturbed when mortality diminishes. Hence, we propose a more modest vision of demographic systems.