Evidence now exists for evolutionary important types of heritable nucleic acid change other than those of base substitution, rearrangement and ploidy changes. Gene conversion and unequal crossing over, for example, may be important not only in the concerted evolution of multigene families but also in speciation and phenotypic trends.7 Another mechanism involving the capture of mRNA by endogenous RNA viruses followed by transfer of the information to germ line DNA after reverse transcription has been proposed to explain the inheritance of acquired immunological tolerance.8 This mechanism was extended as a general theory of evolution in which clonal selection and amplification of particular genes and mRNA species precedes transfer of the amplified information to the germ line.9 The theory, permitting inheritance of acquired adaptations, has however not been well corroborated even in the special case of immunological tolerance.10 It does involve transient information storage in numbers of particular cell types and RNA species before fixation in the structure of germline DNA.