The old way of thinking saw DNA–the bricks and mortar of our genes–as a master molecule. Cancer was thought to arise through the inheritance of bad genes or by damage to good genes (mutations). The new thinking acknowledges that cancer can arise trough a third route: by changing the behavior of genes. The study of how substances alter gene expression is part of the field of epigenetics. Some chemical exposures appear to turn on and turn off genes in ways that disregulate cell growth and predispose for cancer. From this perspective, our genes are less the command-and-control masters of our cells and more like the keys of a piano, with the environment as the hands of the pianist.

Sandra Steingraber. Living Downstream: An Ecologist’s Personal Investigation of Cancer and the Environment  (Foreword to Second Edition). Da Capo Press. Kindle Edition.