We have come to think that if something is in our genes", it is our inevitable destiny. However, this is a gross oversimplification. We have each inherited a particular set of genes, but the outcome of that inheritance is not fixed. Our environment, diet and circumstance flood our bodies with molecules that switch the genes on or off. The result can make a huge difference to our destiny - and that of our descendants. One example of these "epigenetic" changes occurs when a bundle of carbon and hydrogen atoms known as a methyl group attaches itself to the DNA and changes the way its instructions are carried out. Methyl groups often come from what we eat. Lack of food seems to have an epigenetic effect, too. A study of Dutch women starved by the Nazis during the second world war ... found elevated levels of schizophrenia, breast cancer and heart disease. The data suggest that the alterations to which genes are turned on or off survive at least two generations: the one that suffered in the womb during the famine, and their children. They may go much further. A 2011 study published by researchers at the Salk Institute in La Jolla, California, demonstrated epigenetic mutations that lasted for at least 30 generations in plants. What you eat, what your mother ate, the age when your grandfather started smoking, the amount of pollution in your neighbourhood - these factors have all been linked to epigenetic changes that get passed down through the generations. Armed with this new insight, we can take far more control of our health - and the health of future generations.