 Dawkins offered two reasons for organisms not being able to function as replicators. The first is the one he uses to delineate evolutionary genes. As is the case for long stretches of DNA, organisms are too easily and frequently broken up to be considered units of replication. A second reason is that they cannot pass on changes in their structure, although some phenotypic change may result in generational change. In fact, some epigenetic mechanisms have been shown to be passed on across generations (Jablonka &amp; Raz 2009; see the entry on  inheritance systems).  The amount of DNA that counts as a replicator certainly varies; but, according to Dawkins, nothing more inclusive than the genetic material functions as replicators in biological evolution.