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YOU ARE WHAT YOUR GRANDPARENTS ATE
The cancer clue
Dr Michael Skinner believes similar changes may contribute to diseases such as breast cancer and prostate cancer. Both diseases are becoming more common and Dr Skinner says that cannot be attributed to genetic mutations alone. He believes that his team's findings suggest exposure to environmental toxins may play a key role in the evolutionary process.
Professor Alan Boobis, a toxicologist at Imperial College London, UK, told the BBC News website the findings were interesting, but he said there was no need for people to be alarmed. 'This effect is likely to be concentration dependent, and these animals were exposed to very high levels of chemicals,' he said. 'We need to find out whether this trans-generational effect is translated to much lower doses.'
But Dr Pembrey was prepared to stick his neck out further. He suggested an adaptive role for epigenetic inheritance in higher organisms such as humans. He speculated that the inheritance of epigenetic factors which control a few select genes may have enabled human populations to regulate the growth of individuals according to food availability.
Food shortages could generate physiological responses in adults: perhaps a change in hormone levels that influence the activity of key growth genes. This could then be passed on to their offspring. In this way, if the offspring also passed those epigenetic changes on to their offspring, it could result in generations of progressively smaller people, until a period of plenty created the epigenetic changes that reversed the trend. The two generations of small babies that followed the Dutch famine could be explained by just such epigenetic adaptation.
Dr Marilyn Monk, a molecular embryologist and geneticist, and a colleague of Pembrey's at the Institute of Child Health in London, believes this is the tip of an iceberg. She predicts that many more examples of epigenetic inheritance in mammals will come to light once geneticists develop ways to monitor these changes across the entire genome during an embryo's development.
But not everyone is as convinced. John Maynard Smith, an evolutionary biologist at the University of Sussex, is still sceptical. He points out that, even if epigenetic modifications occur naturally in mammals and are passed down the generations, there is still no reason to suspect that they are any more 'adaptive' than random gene mutations that are passed on to offspring. Reik, too, warns that 'such epimutations have any adaptive significance remains to be established'. As yet, no-one has shown that inherited epigenetic changes occur naturally in mammals and even if they did, they may still be rare, random and inconsequential events.
But they might also be downright dangerous.
The final verdict on the significance of epigenetic changes still remains unclear. But one thing is clear: 'Epigenetics matters', according to Lawrence Hurst, an evolutionary geneticist at the University of Bath. As the human genome project rushes to completion, the really interesting insights are going to come not from the DNA and gene sequences, he predicts, but 'from working out how genes are controlled'.
It is in this respect that our environment and the things we do today may have profound effects on our future generations.
Part 4: Cancer Clue | Part 5: Conclusion and References
Last updated 17 November 2009
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