http://discovermagazine.com/2013/may/13-grandmas-experiences-leave-epigenetic-mark-on-your-genes#.UsAuRrSafqp
"...stress is a big suppressor of maternal behavior,” she says. “We see it in the animal studies, and it’s true in humans. So the best thing you can do is not to worry all the time about whether you’re doing the right thing. Keeping the stress level down is the most important thing. And tactile interaction — that’s certainly what the good mother (rats) are doing with their babies. That sensory input, the touching, is so important for the developing brain.”