A Brief History of Everyone Who Ever Lived: The Stories in Our Genes

by Adam Rutherford

Malnutrition can affect the body in many ways, but one of the ways the external world interacts with our inborn biology is via the domain of epigenetics, a word that literally means ‘in addition to genetics’. DNA does not change in a person’s lifetime (unless affected by random mutations from emerging cancers, or caused by attacks from radiation or other mutagens). But with all DNA being present in all cells, mechanisms are needed to make sure only the right genes are on at the right time. Epigenetics is one such system of gene regulation – a way of modifying DNA without altering the gene sequence itself. Think of DNA as an orchestral score, the notes on the page incorrigible and unchanging. If you buy the sheet music to Beethoven’s Seventh Symphony, it is the same notes whether it was published in 1816, 1916 or 2016. How it sounds when played by a full orchestra is another matter though. A conductor and each player in an orchestra will interpret the notes and place annotations on the manuscript to dictate how the music sounds, with crescendo and diminuendo and adagio. Each performance is unique, even when the original scores are identical. In DNA, the notes never change, but they get annotated in all sorts of ways. The most common is via small molecular tags called methyl groups; it’s simply a carbon atom attached to three hydrogens, and these stick in humans onto the nucleobase C (cytosine) in DNA. This has the effect of silencing that bit of DNA. If it’s in a gene, that...