Oxytocin
Oxytocin (Oxt) is a peptide hormone and neuropeptide. Oxytocin is normally produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, sexual reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to stretching of the cervix and uterus during labor and with stimulation of the nipples from breastfeeding. This helps with birth, bonding with the baby, and milk production. Oxytocin was discovered by Henry Dale in 1906. Its molecular structure was determined in 1952. Oxytocin is also used as a medication to facilitate childbirth.
Endocrinology of parenting
However, experimental results are less conclusive. Nulliparous mice do not respond to pup calls, but when administered with oxytocin, they do. A similar study conducted by Holmon and Goy tested nulliparous rhesus females, where post injection did not elicit a drastic response to infants, however there was a notable change in the adult's behavior, including increased proximity and touching. Oxytocin is more often described as a hormone that facilitates bonding and not one that directly increases care. Also, the mice were responding to pup calls and the rhesus macaque infants weren't necessarily providing cues. Similar to the explanation provided for the variation in estrogen and progesterone, rhesus macaques live in drastically different environments. Saltzman proposes that this is due to primates living socially and having a slower developmental trajectory, in which learning is more important.