Why do we see generations coming and going in distinct waves throughout all the history of our civilization? After all a reproductive capacity of humans do not fluctuate significantly year around and has not been having notable cliffs and precipices, which we can dig from a ground or from written records.
As a matter of fact, the number-of-living-humans curve had progressed more or less steadily until it started to sharply accelerate during the past two hundred years or so, perfectly in tune with what we know about how bacterias colonies grow.
That is not a new news, right? Then, shouldn’t generations been flowing smoothly all those times, fluently intermingled — like waters of a big river to which thousands of smaller creeks are joining haphazardly here and there? So, where that cyclicality we observe in history-breaking events come from?
It can be explained by the existence of nutrition (or, in case of humans, structural) barriers.
What is that?
There is a good way to understand and even to see how it works from observing the evolution of a bacteria on a Petri Dish, which was divided into several adjacent sectors each with different types of nutrient cultures which cause bacterias to mutate on their second, log (logarithmic) phase of growth.
A culture barrier sharply reduces the number of surviving and passing into the next sector bacterias from the same batch. That creates a natural filter which both reduces bacterial population and changes its nature by mutations.
Now, because some humans have the adapting ability to alternate their behavioral pattern according to changing environmental conditions (f.e. by learning new skills) they can pass that structural / bureaucratic barrier, which a growing civilizational complexity necessitates. However, most humans do not have two important prerequisites for that behavioral upgrade because they were born into nutrition-poor cultures.
As civilization grows only a few selected by birth-rights species pass through those increasingly higher barriers / filters made of a favorable geography / citizenship, a parent income / social status, an availability of education, a talents roulette etc.
The winners become then capable to impose their will over their batches peers and, eventually, to block remaining talents from passing those barriers. As a result winners stay on a top all times until they reach their 70–80th, changing an arc of history on their way. That’s how their individual, biological lag, log, stationary and decline phases become the phases through which societies they govern also have to pass.
Those are generational waves.
To learn more: http://evernomics.com/