Octopine dehydrogenase (Odh) was examined in several species of bivalves and gastropods and complemented with bibliographic data, to assess the controversy between neutralism and selectionism in explaining the maintenance of genetic variation in natural populations. This debate was the center of the molecular evolu­tion and population genetic research in the 1970s and 1980s, but waned thereafter, without resolution. Although DNA data have been produced, implications are not understood. We examined the polymorphims of Odh in sev­eral species of bivalves and gastropods, and the kinetic properties (apparent K,J of the different isozymes in the scallop Euvola ziczac that indicates an apparent case of overdominance of the heterozygous individuals. The question "which of the two hypothesis is correct" has shifted with time to "how much influence did each factor have in the maintenance of genetic variation".
Keywords: Polymorphism, octopine dehydrogenase, neutralism, selectionism