Only systems containing elements or subsystems capable or propagation, reproduction can undergo natural selection and thereforebiological evolution. The reproduction mechanism can differ. Growth followed, after a certain period of time or after achieving a certain size, by division into two or more daughter individuals probably seems most natural to us. However, it should be emphasized that this is a highly “biocentric” point of view and, in actual fact, reproduction can occur through a quite different mechanism. Some transposons or viruses are actually copied and inserted to a new site on the genome, while others only rewrite a certain section of the DNA according to their own sequence in a process of gene conversion. Thus physical reproduction does not actually occur at all; what is reproduced is the number of copies of certain information.