‘Epigenetics’ has meant various things in scientific thought but, as defined now, it represents the sum of genetic and non-genetic factors acting in cells to control (selectively) the gene expression that produces development and evolution.
Humans may be ‘99% ape’ genetically but our human features in our legs alone (to say nothing of our head and brain) add up to a phenotype difference of more than 1%. The discovery, in the latter part of the last century, of the importance of gene switches, has shown how small genetic change at a critical point in development can lead to big differences in final shape and function. Non-genetic mechanisms that can be inherited go a long way to completing the picture of how the genes we share with fruit flies and mice can produce such diverse organisms.
This multiple-author book deals with current aspects of study into the subject. If the reader's knowledge of genetics is rather rusty then it is hard going and reading it will be punctuated with extensive revision using an up to date textbook. The mechanisms described include methylation of cytosine in DNA, which alters gene expression and which can be inherited. Processes that alter the histone protein component of a chromosome affect the shape of the DNA molecule, thus affecting which parts can be exposed to those switches that allow genes to be expressed differently in cells with identical genomes. Again this can be preserved through mitosis.
The largest section of the book deals with vertebrate organ development, diseases and evolution but a controversial question is discussed as to whether behaviour, especially learnt behaviour, can produce such heritable changes. If this is so then it can be argued that, as a mechanism for evolution, learning could operate at an order of magnitude faster than genomic alterations alone. This was the subject of a recent symposium at the Linnean Society. However most of the 23 fully referenced chapters deal with up to date reviews of ideas about epigenetic effects on, for example, evolution of limb development, the role of skeletal muscle in the shaping of organs and limbs and epigenetics in adaptive radiation.
For the reader looking for an introduction to the subject this book is suitable but it is not holiday reading. For those needing an up to date review on the state of the art, the book will fit the bill precisely. Either way, it will go a long way towards making the reader re-evaluate any ideas that the evolution of variation is purely due to small genetic change.