ABSTRACT
Nonhuman mammalian mothering is hormone-dependent; hormonal changes occurring during pregnancy and labor causally determine the expression of maternal behavior. Studies in animal models have shown that experimental manipulations on the expression of key hormones markedly alter or totally eliminate the expression of maternal care (Feldman, 2012b, 2016; Lonstein, Lévy, and Fleming, 2015; Pryce, 1996; Rosenblatt, 1994; Rosenblatt, 2003). Research in rodents describes the critical role of oxytocin (OT) and prolactin (PRL), which undergo substantial changes during late pregnancy (PRL) and surge at birth (OT), for the onset of maternal behavior. In parallel, hormones associated with the stress response, particularly corticosterone (cortisol in humans), modulate maternal vigilance and active protection of offspring (Brummelte and Galea, 2010; Mann and Bridges, 2001; Pedersen and Prange, 1985). Finally, animal studies point to the involvement of vasopressin (AVP) and testosterone (T) in the emergence of fatherhood and the expression of mammalian paternal care (Carter, 2014; Wynne-Edwards, 2001). In combination with sex-related hormones (estradiol, progesterone), these hormones establish the neuroendocrine milieu that enables rodent mothers—and fathers in the 3%–5% of mammalian species who are biparental (Braun and Champagne, 2014; Kleiman, 1977)—to parent. The hormones of parenting enable parents to recognize infants as rewarding stimuli, protect infants from harm, nurse, express species-typical parental behavior, and provide external regulation for the infant’s immature regulatory systems, including sleep organization, thermoregulation, autonomic functions, attention, and exploration (Feldman, 2016; Hofer, 1995a,b; Numan and Stolzenberg, 2009). These hormones also help parents usher their young into the social niche and accommodate its distinct features. Finally, the neuroendocrinology of parenting promotes the infant’s ability to manage life in harsh ecologies via mechanisms of endocrine fit and the effects of parental hormones on the infant’s brain maturation and social fittedness (Feldman, Monakhov, Pratt, and Ebstein, 2016).
