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29/08/2014

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The Huxley Debate: Are epigenetic changes inherited?

The Huxley Debate: Are epigenetic changes inherited?

By Lizzie Gemmell
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Yesterday evening scientists and interested public gathered for the British Science Festival’s Huxley Debate, which saw Tim Spector (Professor of Genetic Epidemiology at Kings College, London) take on George Davey-Smith (Professor of Clinical Epidemiology at the University of Bristol) to debate the controversial new field of epigenetics. The session was chaired by Lisa Jardine, President of the British Science Association.

‘Epigenetics’ are chemical changes to our DNA which influence how our genes are expressed without actually altering the genetic code. Tim explained that the reason people are so excited about epigenetics is that they offer a mechanism through which the environment can influence our body, risk of disease, and even behavioural traits. For example, smoking has been linked to epigenetic changes which increase the risk of cancer. The controversy around epigenetics lies in whether these patterns of chemical modifications can be passed down through generations, i.e. whether your grandparents smoked increases your risk of cancer.

Each debater was given five minutes to present their opinion. First up was Professor Tim Spector, who put forward the idea that epigenetics are inherited, and that they can explain the differences between genetically identical twins. Tim suggested that epigenetics allow our bodies to adapt to environmental changes and can be passed down through generations in parallel to Darwinian evolution. To back up his theory, Tim referred to recent animal studies demonstrating that stress-induced epigenetic changes were transmitted through four generations of rodents, and suggested that there’s no reason to think that humans aren’t the same.

Professor George Davey-Smith then countered with his theory that epigenetics are limited to single-generation modifications. George argued there is too much hype around epigenetics, and that new techniques shouldn’t undermine hundreds of years of genetic research. George then explained how DNA is stripped of most epigenetic modifications twice during the genesis of gametes, and that the amount remaining is so miniscule that it cannot possibly be important. Therefore, he argued that epigenetic changes develop during our lifetime, beginning with very early exposure to different environments in the womb. He proposed that epigenetics then act to mediate environmental and genetic factors to modify disease risk.

At this stage, Lisa stepped in to recap and invite the audience to join the debate. She commented on how the two arguments seemed to differ on the fundamental point of cause and effect, and how while George’s theory explained how epigenetics modify disease risk within a single lifetime, Tim’s theory went beyond disease to offer a tantalising explanation for the soft inheritance of behaviour and other characteristics that might be passed on.

The audience then joined the debate, raising questions such as how can epigenetics influence evolution and selection? How long do epigenetic changes persist after exposure to an environmental stimulus like smoking? And is risk of disease really just due to so many factors it might as well be chance? These questions proved difficult to answer, with Tim arguing that while we still don’t understand all the mechanisms involved we shouldn’t dismiss them as chance, or we won’t advance science. Conversely, George maintained that there’s just no evidence of transmission of risk or behavioural characteristics through epigenetics.

As we finally filed out of the theatre an hour later I could hear lively debates still raging all around me. Whatever your opinion on the outcome, the session had certainly achieved what it set out to do; inspiring and stimulating further questions and discussion about this exciting new field of research.

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