Epigenetic studies are now beginning to answer these questions and so ‘nurture’ is about to succumb to the kind of detailed biological investigation that has enlightened ‘nature’.  We know that certain genes are epigenetically marked by ‘nurture’ sufficiently to alter their behaviour and the consequent development of the maturing offspring: the environment is leaving an epigenetic birthmark on the genome.

In 2004, Moshe Szyf and Michael Meaney’s team from McGill University, Montreal published a paper in Nature Neuroscience that set the scene for epigenetic studies of parenting. The study suggests that the style of parenting determines the epigenetic modification to gene(s) in the offspring. The research team noticed that maternal behaviour affects the response of young rats to stress. Some mothers licked and groomed their pups a lot (high licking/grooming termed high-LG) while the other kind paid much less interest (low licking/grooming, low- LG). Furthermore, maternal licking and grooming tunes the response of a group of major glands, the hypothalamic-pituitary-adrenal (HPA) axis, by controlling the amount of natural steroids and hormones they release in the face of a stressful or frightening situation.

Rat pups with high–LG mothers were less fearful and their HPA axis reacted less dramatically than in their peers raised by low-LG mothers.  When pups born of low-LG mothers were swapped at birth and nurtured by high-LG mothers (cross-fostering) the outcome was very revealing – the pups were less stressed, like those of high–LG mothers. This showed that the grooming effect was most likely being elicited in the offspring by an epigenetic rather than a genetic factor (i.e. one that is malleable).