depleted during pregnancy that were contained within the placenta. This was later disproved by studies on rats and other species showing that a wide range of animals do not typically decrease the amount of food or water taken in prior to delivery, and that rats presented with placenta will consume it regardless of pregnancy or virginity. Cleanliness and protection against predation Another aspect of placentophagy that was initially considered a beneficial reason for its occurrence was that the consumption of the afterbirth ensured cleanliness of the nest and eliminated any sign of new/vulnerable offspring. It was suggested that nesting animals, who would then rear their young within the nest, benefited by having an aseptic area. Further, predators would be attracted to the site of parturition by the scent of blood and of fetal tissue, so ingesting the afterbirth would eliminate the ability for predators to easily locate newborns. This would in turn provide protection for the defenseless young. These hypothesized benefits were later rejected because the act of consuming the placenta would be more time-consuming than merely abandoning the site of parturition or removing the afterbirth from the nesting area, each of which would provide the same benefit as placentophagy was presumed to provide. Increased pain threshold A newer hypothesis about the maternal consumption of afterbirth in mammals is that the placenta contains compounds that increase pain tolerance post parturition. Although it is known that during pregnancy and labour there is a natural increase in internal production of enkephalins and endorphins that decrease the sensation of pain, studies indicated that the consumption of placenta by maternal rats after delivery spiked the subsequent numbers of these opioids. This was due to the active ingredient present in the placenta as well as the amniotic fluid, placental opioid-enhancing factor (POEF). It is important to note that afterbirth also contains amniotic fluid, and scientists believe its consumption may be equally as important in the elevation of pain threshold as is the placental ingestion. Amniotic fluid is likely taken in unknowingly by cleaning the genital area prior or post delivery, or by cleaning or kissing the infant soon after expulsion. Evolution Placentophagy evolved independently in different lineages as adaptations to various challenges faced by ancestral species. The behaviour was ultimately attractive to the maternal subject based on the hypothesized benefits discussed above but provided some kind of advantage. Based on this advantage, placentophagy was selected