Demographic evolution, like all living phenomena, undergoes a Darwinian process. Species evolve not only physically, but also psychologically, and behaviorally, so there are movements or upheavals in the masses evolution of which the individual is not conscious, but which affect even more the demographic trends than the conscious ones. We could bear in mind that demographic trend cannot be based solely on statistical data of deaths and births. It is a complex phenomenon that adjusts itself, likely as a consequence of previous factors.