Our studies overall examine the effects of our species’ developmental system, or evolved nest, on child and adult well-being (physiological, social, moral). Self-directed free play with others, especially others of multiple ages, is part of humanity’s evolved nest heritage. Other components of the evolved nest for young children that we are relating to well-being include breastfeeding, a welcoming social climate, positive touch and no negative touch, responsive care from several adult caregivers, nature immersion and connection, and routine healing practices.
In this study, we examined the effects of free play on vagal tone. Free play excludes organized sport activities or activities that adults direct. Instead, it refers to spontaneous, imaginative play that children invent together on the fly.
Animal studies show numerous effects of free play on neurobiological and social development. Over 1,200 genes are epigenetically (“turned on or off”) affected by play (Burghardt, 2005). In children, self-regulation systems are beneficially affected by play—delay of gratification (Cemore & Herwig, 2005) and emotion regulation (LaFreniere, 2011; Lindsey & Colwell, 2013). Executive functions are also facilitated by play (Thibodeau et al., 2016).
Our study was the first to examine and demonstrate the relation of play to adaptive physiology.
Adaptive physiological systems are part of a healthy personhood. Adaptive means that the body is able to adjust to the situation at hand—raising heart rate under challenge or decreasing heart rate when in a relaxing situation. Play facilitates the growth of an adaptive physiology.
We measured adaptive physiology with respiratory sinus arrhythmia (RSA), the flexible responsiveness or adaptability of the vagus nerve (the 10th cranial nerve that innervates the major organs of the body). As part of the parasympathetic system, the vagus nerve inhibits the sympathetic nervous system’s threat-defensive systems (flight, fight, freeze). We refer to a vagus nerve response as “vagal tone.” Healthy vagal tone is associated with positive emotions and executive functions.
RSA is calculated by measuring how heart rate and breathing covary in situations of calm and situations of stress. Tonic vagal tone is measured at a single timepoint during relaxing situations, a baseline situation. Phasic vagal tone is measured across conditions—nonstressful to stressful and stressful back to nonstressful. Phasic vagal tone captures how adaptive the vagal tone of an individual is.
Our participants were mother-child dyads who were part of a longitudinal study. They came to the laboratory when the children were about five years old. There were 78 pairs with complete data.
To obtain a proxy for the children’s play experience generally, mothers completed a questionnaire about their child’s recent experience of the evolved nest (Evolved Developmental Niche Report; Narvaez et al., 2019). The play score was derived from two questions: In the past week, how much did the child play actively and freely with other children outside (play organized by the children; not organized activities)? and How much did the child play actively and freely with other children inside (play organized by the children, not organized activities and not passive watching).