Classes

Low.
Middle.
High.
Call them whatever names, they are essentially layers of people within society who:
- have nothing
- have enough
- have too much
The middle one carries the society on their physical shoulders, the high on it's financial ones. And those who have nothing are watching to see what's going to happen next. No bad feelings here, just hard, cold facts.
In a free society the movement between these three levels is also free. Up or down. But it's minimal and is largely dependent on individual skill and educational levels. It is highly unlikely (however possible) to see examples of extremes, or somebody crossing the boundaries from bottom to the top or vice versa. The boundaries, however imaginary and consequently flexible are almost like set in stone as a guideline for all of us: "you belong here, and no, you don't".
We are all born the same, tabula rasa waiting to get filled up with teachings and experiences. We are all going to become princes or the paupers based on the circumstances and  who raised us.
So, it isn't genetics. It is money, and our insatiable appetite for more. Again. 

MG