First aired on Quirks and Quarks (02/02/13)
Which influences humans more: nature or nurture? It's a question that has come up in many scientific debates. Dr. Tim Spector, a genetic epidemiology professor at Kings College London, runs the TwinsUK registry, which is geared to provide an answer to that very question. He and a team of scientists are now finding the two are intermingled in a surprising way: the environment (nurture) can change your genes (nature).
"Even if your genes are identical, you're still a very different person and you can, in a way, alter your genetic destiny," Spector, author of Identically Different: Why You Can Change Your Genes, told CBC's Quirks & Quarks in a recent interview. He and a team of scientists have studied about 11,000 identical twins -- pairs that have identical DNA in every cell of their bodies. Although identical twins look and speak alike, the scientists found that beneath those superficial similarities, twins have many differences; for instance, they often die of different diseases.
Identical twins can end up having different diseases because the way that human genes work is affected by other chemical processes occurring in our cells, Spector explained. These chemical signals can attach to genes and, like a dimmer switch, switch them on or off. This can make humans more susceptible to diseases like cancer or obesity.
As an example, Spector cited the Dutch "Hunger winter," which affected a third of the country's population. As the Germans retreated at the end of the Second World War, they placed a blockade on food shipments to the western part of the Netherlands. Epidemiologists found children who experienced this winter were generally shorter, fatter, and more likely to
suffer from diabetes and schizophrenia. Their descendants shared these traits. The environmental mark of the famine, which told the children's bodies to conserve their energy and shut down some of those genes, was still present in the next generation. Some of the obesity epidemic the Western world is experiencing today could have emerged from famines, he said.
This science "is absolutely the crux of most cancers," Spector said, as behaviours like smoking can switch off a person's protective genes,leading to the initiation of cancer. Cancer then disarms the body by switching off the rest of its protective mechanisms and spreads throughout the body.
Based on this science, drug companies are now developing medicine that reverses cancer's epigenetic function. Four such drugs are already available in Western countries. "So it's becoming a sort of battle -- epigenetic battle -- between us and the cancer, in who can manipulate our epigenome to allow us to survive," he said.
Spector hasn't figured out what environmental factors cause our genes to switch off yet, but science is working on it. "Once you track down what can switch it," he said, "you can also work out what maybe can reverse it."