Epigenetics: Earlier, I said that even if two people ended up with exactly the same genes, that wouldn’t guarantee that those genes would work exactly the same way inside of them. How can that be? Well, it turns out that there is more interaction between your environment and your genetics than previously thought. The environment can change the way genes act, and once these changes occur, they can sometimes be passed on to offspring in the next generation. If that happens, it affects more than just the individual, it affects evolution.
Epigenetics is not what Jean-Baptiste Lamarck considered “the inheritance of acquired characteristics,” although it may seem like it at first. For Lamarck’s idea to work, mutations would be needed in the DNA. Epigenetics—the “epi” means from outside—doesn’t cause a mutation in a gene. It doesn’t alter the way the DNA manuscript is written; it alters the way it is read. To say it another way, epigenetic events don’t add new information to our genome. They change the way that genome is expressed in a person.
A number of epigenetic phenomena have been identified now. For example, in the “Hunger Winter,” the “Dutch Famine” at the end of World War II, thousands of people in the Netherlands starved as a result of Nazi occupation. Children born to pregnant mothers who suffered through this famine and lived have, as adults, shown higher rates of obesity and coronary heart disease than comparative control groups who did not experience starvation. How could this happen?
Well, to simplify, you have a lot of genes and not all of these are active at every given moment. Genes have, for want of a better term, “switches” that tell them when to turn on and when to turn off. Some genes are active during the fetal period but get turned off later. Other genes are inactive until they are turned on during the various stages of growing up and aging. In the normal course of a life, some genes may never be turned on. However, stressful events, such as the starvation people experienced during the Hunger Winter, can sometimes activate switches that wouldn’t normally be activated. This turns genes on or off, thus changing the way a person’s genome builds the structure of their bodies.