The irises and pupils of human and some animal eyes come first to mind. Then there are the spreading waves of drops falling into still water. The full moon and the sun seen through fog appear as circles, as well as some aspents of flowers. There may be a few more natural circles, but not many. Roundish things, however, are much more common. And the roundness of rounded things may often be seen as an approximation to circularity.

Suppose, furthermore, that many human designs and constructions, from art to architecture, had for long implicitly used circles and circularity, even before the distinctly circular form was recognized.

As it has happened, this is not the case for circles, which have been everknown. But ti does happen to be the case for triadic dualism, ancient in being, more prolific in nature and human use even than the circle, but never explicitly recognized nor named until I did so some thirty years ago, around 1972 CE.