Genetic variation is a prerequisite for biological evolution. Indeed, mixed populations of parental forms and di¡erent genetic variants are the substrate for natural selection which is exerted by the living conditions encountered by the organisms. It is still a widely spread opinion that genetic variants spontaneously result from errors and mistakes made during replication or accidents happening to the DNA resulting in changes in the base sequence. With a similar attitude mobile genetic elements are often considered sel¢sh or parasitic, and rare, non-reproducible recombination events are called illegitimate. In the following considerations, I will defend a di¡erent view which I have already propagated for a number of years [3^6