A term credited to Waddington in 1942, although it seems to go back to Oscar Hertwig (1849-1892) who referred to it in his book Biological problem of today: preformation or epigenesis? (1896). For Waddington, it denoted a branch of biology concerned with studying how the phenotype develops as a consequence of interactions between structural genes and their products (i.e., the phenotype), but without change in the sequence of nuclear DNA. What developed according to Waddington was the epigenetic system, which he defined as one in which there was an ongoing balance achieved between genetic instructions, phenotypical changes and environmental influences that brings about development of the zygote into a reproductive adult. In recent years, there has been considerable progress made in understanding epigenetic mechanisms, which include DNA methylation, histone acetylation and RNA interference, with their effects activating and suppressing gene action. As consequence, epigenetics is given a central role in evolutionary developmental biology.
See Baldwin effect, Canalization, Diachronic biology, DNA (deoxyribonucleic acid), Epigenetic emergence, Epigenetic landscape, Epigenesis, Evolutionary developmental biology, Genetic assimilation, Genotype and phenotype, Histone, Methylation, Oligogenic mode of inheritance, RNA (ribonucleic acid)