Possible mechanisms for initiating macroscopic left-right asymmetry in developing organisms

Systematic left-right (L/R) asymmetry in development --i.e. body axes satisfying a ``right-hand rule'' -- emerges at the organism level out of the microscopic handedness of biological molecules, not by the usual pattern-forming mechanisms of reactions (including regulation) plus diffusion, but rather (at the cell level) from the cytoskeleton and molecular motors -- usually in collective two-dimensional states associated with the cell membrane~\footnote{C. L. Henley, Landau 2008 conference\ (arxiv:0811.0055)}. I outline possible scenarios we are simulating for (i) snails and C. elegans, from a chiral shearing tendency in the actomyosin layer and/or (ii) for plant cells, from a precesson of the nematic order direction in the microtubule array.