This is an extremely narrow focus for a term that was originally meant to be about basically everything besides genes that contribute to an organism's phenotype (this idea was developed by the great, rather underrated, 20th century biologist Conrad Waddington). Lotsa epigenetics research by the narrow definition (i.e. modifications to histones and chromatin) focuses on how cells - not organisms - retain their identity/function (or, phenotype). Epigenetics in the narrow sense are important determinants of an organism's phenotype, but these alone are insufficient to understand how and why organisms' become the way they are. Yes, the narrow definition leaves room for environmental influences on gene expression (though "environment" could refer to the state of affairs within a cell or an organism, in addition to the outside world). But it nevertheless imparts agency solely to genomes in affecting an organism becomes.
And this is what the aforesaid book and review are about. Wagner asks, "what would be lost if the original perspective of epigentics [as defined by Waddington] was lost to science?" This is important because an organism is not simply a robotic readout of its genes, but people cannot seem to shake this centuries-old biological determinism.
|Is that a homunculus|
in your [sperm's]
This latent desire to essentialize biology to some singular determinant (be it an homunculus or a gene) is something people just can't get away from. Srsly, there's a persistent sentiment in biology that Real Science is only the high-profile, lab-coated work in genetics. Along these lines, even I adopted the recently popular narrow view of "epigenetics" a while back when I dated a woman who worked at an epigenetics lab, in hindsight probably so I would sound more like a capital-S Scientist (below).
Hipster scientist. H3S10 phosphorylation correlates with
decreased levels of heterochromatin, possibly regulating
chromosome condensation (Chenet al 2008). Image: bit.ly/zEfPaq
It's abundantly clear that phenotypes arise out of an inextricably complex series of interactions - between genes, proteins, cells, tissues, environments, etc. These interactions do not occur solely at the genetic (or narrow-sense epigenetic) level. Developmental biology helps 'connect the dots' between genes and morphology, but cannot do so by focusing solely on genes and chromatin.
Chen, E., Zhang, K., Nicolas, E., Cam, H., Zofall, M., & Grewal, S. (2008). Cell cycle control of centromeric repeat transcription and heterochromatin assembly. Nature, 451 (7179), 734-737 DOI: 10.1038/nature06561
Feil, R., & Fraga, M. (2012). Epigenetics and the environment: emerging patterns and implications. Nature Reviews Genetics DOI: 10.1038/nrg3142
Gilbert, S. (1996). Resynthesizing Evolutionary and Developmental Biology. Developmental Biology, 173 (2), 357-372 DOI: 10.1006/dbio.1996.0032
Hallgrímsson B and Hall BK, eds. 2011. Epigenetics: Linking Genotype and Phenotype in Development and Evolution. Berkeley: University of California Press.
Wagner, G. (2011). Epigenetics in all its beauty Trends in Ecology & Evolution DOI: 10.1016/j.tree.2011.09.003