Nature, nurture... or neither? Epigenetics is the new twist in an age-old argument

A combination of genes and our environment makes us what we are. Or so we always thought...

Iranian twins Ladan and Laleh were conjoined but had different personalities. The 1983 film Trading Places explored the nature/nurture debate (AP)

It is a shibboleth of family life – that every individual is the product of their genes and environment, the one an immutable inheritance, the other a mutable array of influences and pressures with unpredictable outcomes.

But new research has demonstrated that genes can change, identical twins with the same genetic inheritance can turn out completely different and the impact of environmental influences can be passed down the generations.

The new science of epigenetics has shown that in addition to nature and nurture, what makes us who we are is also determined by biological mechanisms that can switch genes on or off.

These epigenetic (above the gene) "light switches" can affect characteristics as fundamental as autism and sexual orientation.

But they are also subject to environmental influences and thus, in theory, are within our control.

Professor Tim Spector, head of the department of twin research at Kings College, London, who has undertaken the most detailed twin studies in the world, cited the case of Iranian twins Ladan and Laleh, who were joined at the head and shared identical genes and environment and yet had different personalities. The differences led him to question the influence of genes.

"Up to a few years ago I believed genes were the key to the universe. But over the last three years, I have changed my mind," he said at the launch of his book Identically Different: Why You Can Change Your Genes, which challenges the view that an individual's genetic inheritance is immutable.

Studies of the effects of famines in Holland in the 1940s, in China in the 1950s and in the United States over a century ago show they changed the lifespan and obesity rates in subsequent generations. They switched on genes that increased the accumulation of body fat in times of plenty, in order to improve survival chances in times of famine.

In the modern world, with calorie-dense fast foods more freely available than at any time in history, the seeds of the current obesity epidemic may thus have been sown in the 19th century.

"The risk of obesity can come not just from your own environment or your mother's but higher up [the ancestral chain]," he said.

Four drugs with epigenetic effects that can switch genes on or off are already on the market and 40 more are in development, he said.

But there are other, natural, ways of controlling them, too. Exercise has been shown to switch off the FTO gene, a key driver of obesity. Diet can also affect gene expression.

"We and our genes are more flexible than we thought," he said.