Souls with great creativity will naturally be drawn to eras when they may express that creativity, unless karma prevents it for one reason or another. In each era people express what they are, and thus each age assumes the tone and characteristics of the people in it who are expressing what they are. If the preponderance of souls is primitive, it will be a primitive age, and so forth. An age is the people living in it, and the destinies or karma they are working out. The great souls of the Periclean Age in Greece are what made the Periclean Age.
Mankind consists of a wide variety of souls.
There is the great run of average people, which includes most of us. Then the forerunners, who are geniuses in a variety of fields, science, literature, the arts. It is difficult to imagine what the fate of mankind would have been if these compassionate ones had not given of their essence for the sake of us all. There are many types of souls connected with the human race. Civilizations simply cannot continue to rise and rise, for very good reasons.