Melatonin is secreted during the dark hours of the night. Therefore, during the short nights of spring and summer, the duration of melatonin secretion is shortened. This drop in melatonin acts as a biological green light, triggering the hypothalamus to release gonadotropin-releasing hormone (GnRH). In layman’s terms: the longer the day, the less darkness, the less melatonin, and the more active the reproductive system becomes.