When a four-year-old breaks a bone, that trauma is not encoded in his epigenome; it doesn’t affect him in the long term. But when a four-year-old experiences chronic stress and adversity, some genes that regulate how the brain, immune system, and hormonal systems respond to stress get turned on and others get turned off, and unless there is some intervention, they’ll stay that way, changing the way the child’s body works and, in some cases, leading to disease and early death. There are a
