Revision of evolutionary theory Non-genetic variation and inheritance, however, proved to be quite common. Concurrent with the 20th-century development of the modern evolutionary synthesis (unifying Mendelian genetics and natural selection), C. H. Waddington (1905-1975) was working to unify developmental biology and genetics. In so doing, he adopted the word "epigenetic" to represent the ordered differentiation of embryonic cells into functionally distinct cell types despite having identical primary structure of their DNA. Researchers discussed Waddington's epigenetics sporadically - it became more of a catch-all for puzzling non-genetic heritable characters rather than a concept advancing the body of inquiry. Consequently, the definition of Waddington's word has itself evolved, broadening beyond the subset of developmentally signaled, inherited cell specialization. Some scientists have questioned whether epigenetic inheritance compromises the foundation of the modern synthesis. Outlining the central dogma of molecular biology, Francis Crick succinctly stated, "DNA is held in a configuration by histone[s] so that it can act as a passive template for the simultaneous synthesis of RNA and protein[s]. None of the detailed 'information' is in the histone." However, he closes the article stating, "this scheme explains the majority of the present experimental results!" Indeed, the emergence of epigenetic inheritance (in addition to advances in the study of evolutionary-development, phenotypic plasticity, evolvability, and systems biology) has strained the current framework of the modern evolutionary synthesis, and prompted the re-examination of previously dismissed evolutionary mechanisms. Furthermore, patterns in epigenetic inheritance and the evolutionary implications of the epigenetic codes in living organisms are connected to both Lamarck's and Darwin's theories of evolution. For example, Lamarck postulated that environmental factors were responsible for modifying phenotypes hereditarily, which supports the constructs that exposure to environmental factors during critical stages of development can result in epimutations in germlines, thus augmenting phenotypic variance. In contrast, Darwin’s theory claimed that natural selection strengthened a populations ability to survive and remain reproductively fit by favoring populations that are able to readily adapt. This theory is consistent with intergenerational plasticity and phenotypic variance resulting from heritable adaptivity. In addition, some epigenetic variability may provide beneficial plasticity, so that certain organisms can adapt to fluctuating environmental conditions. However, the exchange of epigenetic information between generations can result in epigenetic aberrations, which are epigenetic traits that deviate from the norm. Therefore, the offspring of the parental generations may be predisposed to specific diseases and reduced plasticity due to epigenetic aberrations. Though the ability to