Final answer:
The hormone prolactin, produced by the anterior pituitary, plays a key role in lactation by stimulating milk production following childbirth and is regulated by the hypothalamus hormones PRH and PIH.
Step-by-step explanation:
The evolutionary history of prolactin (PRL) is closely tied to that of its regulatory system involving the pituitary gland and the hypothalamus. Prolactin, a hormone produced by the anterior pituitary, is crucial for stimulating milk production in the mammary glands following childbirth. The regulation of prolactin levels is managed by hypothalamic hormones including prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH), which is dopamine. The secretion of prolactin into the bloodstream leads to the stimulation of milk production, which in turn fosters a positive feedback loop where the act of breastfeeding or pumping encourages continued high levels of prolactin.