Mutation breeding, evolution, and the law of recurrent variation

In the present paper the history of the rise and fall of mutation breeding as an autonomous branch of breeding research is documented as well as its positive side effects for plant breeding and biology in general. Perhaps the most important generalization on the basis of the total outcome of mutation breeding will be termed “the law of recurrent variation”. It states that “treating homozygous lines with mutagenic agents generates large, but clearly finite, spectra of mutants. This consistently occurs when the experiments are carried out on a scale adequate to isolate the potential of alleles causing phenotypic and functional Correspondence/Reprint request: Dr. Wolf-Ekkehard Lönnig, Max-Planck-Institut for Plant Breeding Research Carl-von-Linné-weg 10, 50829 Cologne, Federal Republic of Germany. E-mail: [email protected] deviations (saturation mutagenesis).However, due to almost Wolf-Ekkehard Lönnig 46 invisible residual effects of changes in redundant sequences and/or of further chromosome rearrangements, the corresponding saturation curve is asymptotically approaching its limit for the micro-quantitative part of variation.” Also, reasons are given why the law is relevant for heterozygotes and allogamous species as well, and the genetical basis of the law is briefly defined. In addition, arguments are presented why the overoptimism and euphoria at the beginnings of the period of mutation breeding are to be evaluated in connection with the basic assumptions of the synthetic theory of evolution − i.e. the assurance that mutations and selection constitute the entirely sufficient explanation of the origin of all species and higher systematic categories of the plant and animal kingdoms alike. This point established, the question is discussed whether the finite nature of the mutant spectra found in plant breeding research might also have repercussions on the present theory of the origin of species. Providing an affirmative answer of the applicability of the law of recurrent variation not only to cultivated plant and animal lines but also to species in the wild, the statements and assertions of the synthetic theory as quoted below will have to be revised.