The author changes through the 3 stories because the author wants to show that there is a problem in diffrent times. History repeats itself and I think that what the author is trying to say. there is a problem in all of there time periods. the effect on the reader is we have to change our minds to the situation and the problem.
Well said Alejandro. As readers, we do have to shift our thinking to adjust to the various time periods even though the central message is the same.