In addition to late-night breast-feeding extending a mother's post-birth infertility (amenorrhoea), professor and study author David Haig also says, "Night waking increases in the second half of the first year of infant life and is more pronounced for breast-fed babies." How does that connect, though? Well, Haig says that baby's tendency to walk around at night looking to get fed is an ecological adaption in an effort to extend amenorrhoea.
Natural selection plays a part because infants seek to delay the birth of a new baby—infants benefit from this delay as it extends the IBI, or inter-birth interval. A baby's late-night roamings and cries for food essentially suppress a woman's ovarian function, as the infant benefits from more attention and less competition from a sibling.
"Spacing out siblings would give the mother more time to recover from the birth and make young children more independent, boosting their chances of survival, so this research makes perfect sense," Siobhan Freegard, founder of British parenting website Netmums, told The Daily Mail.
In other words, it's all part of Mother Nature's plan.