 The view that evolutionary theory is a theory that applies to active germ-line replicators has come under fire from a multitude of directions. Genes need not be germ-line to undergo selection, as it is at least arguable that the immune system exhibits selection processes (Okasha 2006: 11). Copying is beside the point, since only similarity across generations, rather than identity, is necessary for evolutionary change (Godfrey-Smith 2000, 2007 and entries on  units and levels of selection  and  replication and reproduction).  For his part, Hull seems to agree with this last point, as he allows that organisms might well count as replicators, at least in cases in which they reproduce asexually (Hull 2001: 28–29).