At most four types (groups) of isomers have been revealed, in natural things or as envisaged structures: meso, C2 symmetrical, irrechi, constitutional. In vertebrate almost exclusively constitutional isomers have been found. On the other hand, all fundamental natural combinations, found as constitutional isomers in vertebrates, are able to form symmetric isomers. (Hence, they keep symmetry as a possibility and not as a reality). Symmetric isomers of constitutional ones also possess functional groups. Therefore, a comparison could be made between a real and a possible situation, and an interesting and unique conclusion results from this comparison. A series of symmetric compounds, especially C2 symmetrical ones, have been isolated from plants and microorganisms, however no counterparts of these combinations were ever found in vertebrates. However, a preliminary conclusion could be drawn: symmetry phenomenon is much better represented in plants and microorganisms than in vertebrates. Of symmetric isomers, the meso ones are characterized by a mirror plane of symmetry, i.e. an area capable to hide (mask) atoms or planar structures of polarized light.