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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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The tyranny of causation

Here (a bit late) is my latest Wall Street Journal column, on epigenetic inheritance

In the debate over whether our fates as individuals are ruled by nature or nurture-that is, by innate qualities or personal experience-one of the most baffling features is the way the nurture advocates manage to cast themselves as the great foes of determinism. "Genes don't determine who we are," they insist-all the while positing that environmental causes often do. Remember how some Freudians tried to blame autism, schizophrenia and even homosexuality on the way parents treated their children? True, they claimed these effects were treatable, but so are many genetic problems. I wear glasses to correct a partly genetic tendency to myopia.

Nor has environmental determinism escaped moral stain. When Soviet agriculture was forced to obey crank theories that environmental conditioning rather than breeding could determine the frost-resistance of wheat-not coincidentally echoing the notion that human nature could be remade by communism-the result was famine.

Yet the idea persists that paying attention to genetic factors amounts to fatalistic resignation, whereas focusing on an individual's upbringing affirms freedom and opportunity. Thus do certain quarters welcome any chance to knock genes off their pedestal, including a new set of discoveries that go by the name of epigenetic inheritance.

If your father ate fatty food, it turns out, you may be prone to diabetes (so long as you are a rat). This result, recently announced by scientists in Sydney, is surprising because it has long been accepted that mammals are descended from the sperm, not the bodies, of their fathers. One early geneticist even cut off the tails of 1,500 rats over 20 generations to prove that their offspring did not inherit docked tails.

Yet there's already a hint that the Australian result will apply to people. In Sweden, paternal grandsons of men who experienced a particular 19th-century famine in their youth had lower rates of diabetes and cardiovascular disease. So, apart from its possible medical significance, the fat rats suggest a new form of parental influence, probably through small gene-like RNA molecules smuggled into sperm.

If this result stands up, does it turn evolutionary theory and genetic determinism on their heads? If we can inherit some effects of lifestyle, outside the genetic structure, does this free us from the tyranny of genes?

Hardly. It's hard to feel liberated if we get diabetes because of something our parents did before our birth rather than something they were. There are other tyrannies than genetic ones.

The word "epigenetic" is decades old and refers to the switching on and off of genes during development. Some genes get locked down when no longer needed in particular tissues. Cancer cells, for example, lock down tumor-suppressor genes that would normally halt their spread.

One of the chief locking mechanisms is "methylation," the attachment of a chemical block to part of the gene sequence. In the diabetic Australian rats, one gene was nearly twice as active as normal because this process was much reduced. And what makes the proteins that insert or remove these chemical blocks? Our genes. It looks as if some of those proteins, or the RNAs that trigger the manufacture of those proteins, are carried over into the next generation in the sperm or egg.

The new results are evidence that genes are sensitive to experience. But we knew that. From suntan to memory, lots of bodily things happen because genes are activated by environmental triggers: Genes switch on and off in your brain in response to what you perceive, think and do. That's why the old nature-nurture dichotomy is so misleading. Genes are our slaves as much as our masters.