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
In some studies on females across species, estrogen and progesterone prepartum is also related to oxytocin. Although, the relationships between these hormones is similar across species, there is variation in the degree to how oxytocin effects behavior. For example, in some species, like rats, an increase in oxytocin greatly increases interactions with infants, but an increase in oxytocin in macaques only mildly increased interactions. However, the importance here is that oxytocin increased interactions in all of the relevant cited studies for females, as well as the majority of studies cited for males.