Epigenetic inheritance: a contributor to species differentiation?

Multiple epigenetic states can be associated with the same genome, and transmitted through the germline for generations, to create the phenomenon of epigenetic inheritance. This form of inheritance is mediated by complex and highly diverse components of the chromosome that associate with DNA, control its transcription, and are inherited alongside it. But, how extensive, and how stable, is the information carried in the germline by the epigenome? Several known examples of epigenetic inheritance demonstrate that it has the ability to create selectable traits, and thus to mediate Darwinian evolution. Here we discuss the possibility that epigenetic inheritance is responsible for some stable characteristics of species, focusing on a recent comparison of the human and chimpanzee methylomes which reveals that somatic methylation states are related to methylation states in the germline. Interpretation of this finding highlights the potential significance of germline epigenetic states, as well as the challenge of investigating a form of inheritance with complex and unfamiliar rules.