a delight. Hats off to Nessa! (Although everything is explained, I would warn readers that a basic knowledge of genetics would be an advantage.) Before I read this book my understanding of genetics was quite naive, I thought DNA made proteins, and if there are mutations in the DNA code then that leads to trouble, such as cancer. But only 2% of the human genome makes protein - what is the other 98% for? Also consider this: A caterpillar that becomes a butterfly has exactly the same DNA - so why do they look so different? The answer is 'epigenetics'. Whenever two genetically identical individuals are non-identical in some way we can measure, this is called epigenetics. This also includes an individual at different point in their life. For example why does horrendous abuse as a child often lead to problems later in life - is it psychological or is it embedded in the very genes of the person? In the following sentence, before I read this book, I mostly understood the word 'within'. The author never hides the gritty details from the reader unlike many patronising popular science books that shy away from the scientific detail in case the reader finds it too difficult. She takes you step by step through the main details of epigenetics and the technical language used. It is not difficult, but you do have to take it slowly to digest the information. To make the subject a bit lighter, the book is dotted with