An excerpt from Nessa Carey’s excellent introduction to and explanation of the field of epigenetics, The Epigenetics Revolution: How Modern Biology Is Rewriting Our Understanding of Genetics, Disease, and Inheritance, recently appeared in Natural History Magazine. We have an excerpt from that excerpt here today. In our excerpt, Carey emphasizes that DNA does not entirely dictate human health (with references to Romeo and Juliet and Breakfast at Tiffany’s.
We talk about DNA as if it’s a template, like a mold for a car part in a factory. In the factory, molten metal or plastic gets poured into the mold thousands of times, and, unless something goes wrong in the process, out pop thousands of identical car parts.
But DNA isn’t really like that. It’s more like a script. Think of Romeo and Juliet, for example. In 1936 George Cukor directed Leslie Howard and Norma Shearer in a film version. Sixty years later Baz Luhrmann directed Leonardo DiCaprio and Claire Danes in another movie version of this play. Both productions used Shakespeare’s script, yet the two movies are entirely different. Identical starting points, different outcomes.
That’s what happens when cells read the genetic code that’s in DNA. The same script can result in different productions. The implications of this for human health are very wide-ranging, as we will see from the case studies we are going to look at in a moment. In all these case studies it’s really important to remember that nothing happened to the DNA blueprint of the people in these case studies. Their DNA didn’t change (mutate), and yet their life histories altered irrevocably in response to their environments.
Audrey Hepburn was one of the twentieth century’s greatest movie stars. Stylish, elegant, and with a delicately lovely, almost fragile bone structure, she became an icon in her role as Holly Golightly in Breakfast at Tiffany’s, even to those who have never seen the movie. It’s startling to think that this wonderful beauty was created by terrible hardship. Audrey Hepburn was a survivor of an event in World War II known as the Dutch Hunger Winter. This ended when she was sixteen years old, but the aftereffects of that period, including poor physical health, stayed with her for the rest of her life.
The Dutch Hunger Winter lasted from the start of November 1944 to the late spring of 1945. That was a bitterly cold period in Western Europe, creating further hardship on a continent that had been devastated by four years of brutal war. Nowhere was this worse than in the western Netherlands, which at this stage was still under German control. A German blockade resulted in a catastrophic drop in the availability of food to the Dutch population. At one point the population was trying to survive on only about 30 percent of the normal daily calorie intake. People ate grass and tulip bulbs, and burned every scrap of furniture they could get their hands on, in a desperate effort to stay alive. More than 20,000 people had died by the time food supplies were restored in May 1945.
The dreadful privations of that time also created a remarkable scientific study population. The Dutch survivors were a well-defined group of individuals all of whom suffered just one period of malnutrition, all of them at exactly the same time. Because of the excellent health-care infrastructure and record-keeping in the Netherlands, epidemiologists have been able to follow the long-term effects of the famine. Their findings were completely unexpected.
One of the first aspects they studied was the effect of the famine on the birth weights of children who had been in the womb during that terrible period. If a mother was well fed around the time of conception and malnourished only for the last few months of the pregnancy, her baby was likely to be born small. If, on the other hand, the mother suffered malnutrition only for the first three months of the pregnancy (because the baby was conceived toward the end of the terrible episode), but then was well fed, she was likely to have anormal-size baby. The fetus “caught up” in body weight.
That all seems quite straightforward, as we are all used to the idea that fetuses do most of their growing in the last few months of pregnancy. But epidemiologists were able to study these groups of babies for decades, and what they found was really surprising. The babies who were born small stayed small all their lives, with lower obesity rates than the general population. For forty or more years, those people had access to as much food as they wanted, and yet their bodies never got over the early period of malnutrition. Why not? How did their early life experiences affect these individuals for decades? Why weren’t they able to go back to normal once their environment reverted to the way it should be?
For more information on epigenetics read the rest of the excerpt at the website of Natural History Magazine or read Nessa Carey’s full book, The Epigenetics Revolution.