Living in a physical world XII. Keeping up upward and down downward

摘要

In defining an organism's immediate physical situation, one begins with position and orientation, just as when distinguishing between translational and rotational motion. Position always matters, even if no exact specification need be given for the pelagic or the aerial. Orientation can be ignored in only a few instances - non-motile spherical unicells in a continuous medium, perhaps a colonial Volvox in a pond, under some circumstances maybe bird eggs and round nuts.