All those sleepless night may mean just one thing: your baby is not ready to share mum with a brother or sister and is keeping you exhausted to delay ovulation.
This hypothesis comes courtesy of David Haig, an evolutionary biologist at Harvard University, who explained to Michaeleen Doucleff over at npr that although babies aren’t consciously trying to halt mum’s fertility, they do seem to be fending for themselves by delaying the birth of a new family member.
Haig’s hypothesis is backed up by some convincing arguments. When times are tough – financial crises or pandemics – newborns and toddlers have a better chance of surviving if their parents wait to have more offspring as they don't have to share already limited resources.
“Nursing a child, especially at night, seems to hinder many women from resuming ovulation soon after pregnancy. So if a baby can force mum to feed him at night, she may stay infertile longer”, explained Doucleff.
But not everyone agrees with Haig.
Holly Dunsworth, an anthropologist from the University of Rhode Island, says that Haig’s hypothesis doesn’t factor in all the benefits of nightly feedings, which go from hunger satiation to bonding. “When you look at it from that perspective, waking up to feed looks more like cooperation than conflict”, Dunsworth said.
Like many evolutionary arguments, proving that babies are intentionally tiring out their mothers to make sure they’re infertile longer will be hard to test.
“It’s clear that babies can get enough milk even if they sleep through the night”, Haig said. “I’m just suggesting that offspring have evolved to use waking up mothers and suckling more intensely to delay the birth of another sibling”.