  A computational theory and model of the ontogeny and development of bilateral
symmetry in multicellular organisms is presented. Understanding the origin and
evolution of bilateral organisms requires an understanding of how bilateral
symmetry develops, starting from a single cell. Bilateral symmetric growth of a
multicellular organism from a single starter cell is explained as resulting
from the opposite handedness and orientation along one axis in two daughter
founder cells that are in equivalent developmental control network states.
Several methods of establishing the initial orientation of the daughter cells
(including oriented cell division and cell signaling) are discussed. The
orientation states of the daughter cells are epigenetically inherited by their
progeny. This results in mirror development with the two founding daughter
cells generating complementary mirror image multicellular morphologies. The end
product is a bilateral symmetric organism. The theory gives a unified
explanation of diverse phenomena including symmetry breaking, situs inversus,
gynandromorphs, inside-out growth, bilaterally symmetric cancers, and the
rapid, punctuated evolution of bilaterally symmetric organisms in the Cambrian
Explosion. The theory is supported by experimental results on early embryonic
development. The theory makes precise testable predications.
