Soon, Millennials, we will be overtaken. The trend pieces have already started defining the upstarts, the next generation. As Millennials replaced Gen X, and Gen X replaced the Baby Boomers, and Baby Boomers replaced the Greatest Generation, we, too, will be replaced by the Youth of Today.
This is not, however, some ancient aging curse that's afflicted humanity since the beginning of history. Societal generations are a relatively modern idea, hit upon by 19th century European intellectuals and refined in the beginning of the 20th century.
Back in 1979, the historian Robert Wohl (now an emeritus professor at UCLA) took a close look at "the phenomenon of generational thinking" in The Generation of 1914. Before the 19th century, generations were thought of as (generally male) biological relationships within families—grandfathers, sons, grandchildren and so forth. But in the 1800s, that started to change, Wohl wrote:
One can trace its progress in dictionaries. During the early 19th century the term "generation" was used primarily to signify either the relationship between fathers and their sons or contemporaneity. The French lexicographer Emile Littré defined a generation in 1863 as "all men living more or less in the same time." In the second half of the nineteenth century the term was employed increasingly to connote coevals, and especially to evoke the dichotomy between the older generation and "youth."
The roots of this idea came from the work of French and German philosophers who were, the sociologist Karl Mannheim wrote in 1927, "anxious to find a general law to express the rhythm of historical development, based on the biological law of the limited life-times of man."