“It is certainly as true as the gospel that when a man sleeps with his wife or his mistress with dirty and smelly feet, if he fathers a boy, the child will have smelly and unpleasant breath. If he fathers a girl, she will have a stinky rear end.”
The source of this dubious wisdom is the Distaff Gospels – a cornucopia of medieval old wives’ tales. Expectant mums were advised to avoid eating hares’ heads in case they caused a harelip, skip soft cheese lest their sons be born with small penises, and shun fish heads for fear of giving their child a trout pout – as well as the perhaps more reasonable advice to avoid shagging a man with filthy feet.
Today we laugh at their wrong-headed nonsense. Decades of research into the molecular processes underpinning human development tell us that harelips, trout pouts and small cocks are due to genes rather than anything a mother eats. But there’s an insidious undertone creeping into today’s advice to expectant mums, and it’s coming from the relatively new field of epigenetics.
A word that’s bandied around by some the way “quantum” is – as a non-explanation for biological stuff we don’t really understand yet – epigenetics is all about the interaction of nature and nurture. On one side is nature: the genetic information hard wired in our DNA – the recipes for life. Then there’s nurture: the impact of the environment on how this genetic information gets used.
Our cells “write” epigenetic changes into our DNA in response to changes in the environment using various molecular signals. It’s a bit like sticking Post-it notes into a recipe book, saying: “Use this brownie recipe, not the other one” or “Add more lemon juice here.”
Where things get more controversial is with the suggestion that this epigenetic information might somehow get passed on to the next generation – seemingly in contravention of Darwinian dogma maintaining that characteristics can only be passed on through DNA. But there are a few intriguing examples where this seems to happen.
A couple of years ago researchers showed that baby mice could inherit memories about specific scents from their fathers, even though they’d never so much as caught a whiff themselves. Another research group claims to have found evidence that the traumatic experience of being caught up in the 9/11 attacks was epigenetically passed on to children by women who were pregnant at the time. And there are stories suggesting that a mother’s diet can influence the weight or metabolism of her children, and even her grandchildren.
However, it’s virtually impossible to distinguish the influence of epigenetic changes from all the other stuff that’s going on during the incredibly complex journey from fertilised egg to independent child. And the data are generally pretty weak, at least in the eyes of those who know about these things.
This is important because it matters to people. Pregnant women face a deluge of conflicting information and judgmental criticism about how to do the best for their baby. The evidence of more subtle epigenetic impacts on offspring is hazy, and most of the work has been done on animals rather than people.
What if some overzealous law-maker reads the headlines about how a female rat’s behaviour or diet can epigenetically modify her foetus, and starts drafting a bill dictating what pregnant women can and can’t do or eat? Until the science is more settled, let’s make sure that health advice is based on real, human science.
Herding Hemingway’s Cats: Understanding How Our Genes Work by Kat Arney (Bloomsbury Sigma, £16.99). To order a copy for £13.59, go to bookshop.theguardian.com
