DNA methylation and imprinting: why bother?

DNA methylation is crucial for mammalian development because embryos that cannot maintain normal methylation levels die after gastrulation. I propose that DNA methylation is only important for the somatic lineages, but has no role in embryonic lineages including the germ line. Among vertebrates, genomic imprinting is found only in mammals, and numerous hypotheses have ascribed an essential function to imprinting because of the uniquely mammalian developmental and physiological requirements. However, our understanding of molecular details of the imprinting process, as well as evolutionary considerations, is rather consistent with imprinting having no intrinsic role in mammalian development.