Most mammalian offspring find it distressing when they lose contact with their caregiver (Narvaez, 2013). In infant rats even short separations from the mother can cause lifelong changes in stress responsivity. However, brief and graded separations that are developmentally appropriate can help cope with longer separations later, but otherwise have lasting negative impacts. Even in less social species than humans, physical separation creates painful emotions. Work on rats has shown that multiple systems are regulated by the presence of the mother and these become dysregulated in her absence. Monkeys separated from adults when young produce less serotonin which is inked with impulsive violence and antisocial behaviour in mammals. Excessive separation distress in early development makes the brain vulnerable to depressive disorders later in life.

Physical affection and touch have long-lasting positive effects on health. Maternal touch soon after birth has been shown to effect gene expression in the pituitary-adrenal stress axis. Rats who experienced high touch in the first 10 days of life had higher gene expression for glucocorticoid receptor proteins which are produced in response to stress and need to be well regulated to prevent excessive stress and depression. Rats with less touch had higher anxiety and lifelong heightened response to stress. These effects echoed down the generations as low-nurturing mothers breed low-nurturing daughters, compounding the effects of poor care over generations. The same epigenetic mechanism occurs in humans who were abuse as children and end up dying by suicide. A lack of interpersonal touch between mother and infant has a long-lasting negative impact on emotional development.

In EEA infants were likely in constant physical contact day and night (Narvaez et al). Hidden regulators have been documented during infant-mother co-sleeping which includes regular feeding. Optimal human development is based on social synchrony and the collective intelligence of human groups is based on social sensitivity. Responsive care with ‘co-regulated communication patterns’ is linked with good parasympathetic vagal tone which is essential for a healthy functioning of digestive, cardiac, respiratory, immune and emotional systems. Having a depressed mother with low responsiveness changes the functioning of the HPA axis.

There is a cultural misperception that letting babies cry themselves to sleep represents appropriate parenting. This practice floods babies brains with neurotoxic cortisol. This may wire the brain for oversensitivity and over-reactivity creating dispositions towards depression and anxiety, negative mental and physical health outcomes, accelerated aging and early mortality. It is also linked with use of alcohol for relief of stress. Infant emotional dysregulation is related to increased mental illness and a tendency towards violence. Warm, responsive care-giving is linked with greater stress regulation, greater moral functioning, greater conscience, compassion and open-heartedness as adults (from strong vagal tone). High vagal tone also makes people more co-operative and happier.