As a means of assigning value to entire swaths of humankind, caste guides each of us often beyond the reaches of our awareness. It embeds into our bones an unconscious ranking of human characteristics and sets forth the rules, expectations, and stereotypes that have been used to justify brutalities against entire groups within our species.

Dehumanization distances not only the out-group from the in-group, but those in the in-group from their own humanity. It makes slaves to groupthink of everyone in the hierarchy.

Not one of us was here when this house was built. Our immediate ancestors may have had nothing to do with it, but here we are, the current occupants of a property with stress cracks and bowed walls and fissures built into the foundation. We are the heirs to whatever is right or wrong with it. We did not erect the uneven pillars or joists, but they are ours to deal with now. And any further deterioration is, in fact, on our hands.

While the requirements to qualify as white have changed over the centuries, the fact of a dominant caste has remained constant from its inception – whoever fit the definition of white, at whatever point in history, was granted the legal rights and privileges of the dominant caste. Perhaps more critically and tragically, at the other end of the ladder, the subordinated caste, too, has been fixed from the beginning as the psychological floor beneath which all other castes cannot fall.

More than a century and a half before the American Revolution, a human hierarchy had evolved on the contested soil of what would become the United States, a concept of birthright, the temptation of entitled expansion that would set in motion the world’s first democracy and, with it, a ranking of human value and usage.

Caste and race are neither synonymous nor mutually exclusive. They can and do coexist in the same culture and serve to reinforce each other. Race, in the United States, is the visible agent of the unseen force of caste. Caste is the bones, race the skin. Race is what we can see, the physical traits that have been given arbitrary meaning and become shorthand for who a person is. Caste is the powerful infrastructure that holds each group in its place.

In Germany, displaying the swastika is a crime punishable by up to three years in prison. In the United States, the rebel flag is incorporated into the official state flag of Mississippi. It can be seen on the backs of pickup trucks north and south, fluttering along highways in Georgia and the other former Confederate states. A Confederate flag the size of a bedsheet flapped in the wind off an interstate in Virginia around the time of the Charlottesville rally.

Africans are not black,” she said. “They are Igbo and Yoruba, Ewe, Akan, Ndebele. They are not black. They are just themselves.

What scientists have only recently discovered is that the more familiar earthquakes, those that are easily measured while in progress and instantaneous in their destruction, are often preceded by longer, slow-moving, catastrophic disruptions rumbling twenty miles or more beneath us, too deep to be felt and too quiet to be measured for most of human history.

Caste is insidious and therefore powerful because it is not hatred, it is not necessarily personal. It is the worn grooves of comforting routines and unthinking expectations, patterns of a social order that have been in place for so long that it looks like the natural order of things.