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Babies cry so you won’t have sex

The sound of newborn babies crying at night is an expected rite of passage into parenthood, but did you ever wonder why they cry? We thought they were hungry, but a Harvard researcher thinks they just don’t want siblings.

Couple in bed |

Photo credit: Val Thoermer/Getty Images

Ah, those first few weeks at home with a newborn baby — so precious, yet so incredibly exhausting. New parents try to establish a bit of a routine with their little one, while moving around in a somewhat zombie-like state. While the pediatrician may tell you that those middle-of-the-night cries are from hunger, a Harvard researcher had an interesting theory that goes beyond a nighttime feeding and a diaper change.

Your baby is a libido killer

Harvard researcher David Haig is an evolutionary biologist with a different perspective on these late-night cries. What if babies are making their best attempts at exhausting their moms, which may in turn suppress ovulation and — as any tired parent can attest to — make her too tired for sex? Seems like an ingenious way to ensure that Baby won’t have to share any of the available food and affection from coming from Mom.

“I’m just suggesting that offspring have evolved to use waking up mothers and suckling more intensely to delay the birth of another sibling,” says Haig of his findings, which were published in the journal Evolution, Medicine and Public Health. Anyone who has lived through life with a baby in the house knows that sleep deprivation and sheer exhaustion don’t do a thing for your sex life.

Survival of the fittest (and loudest)

There seems to be an evolutionary aspect to this theory. Back in the early days of man, babies who woke their parents often at night may have been more likely to survive and eventually have children of their own. In more modern times, such as during the Depression, children whose parents delayed having more children had more access to food and a better chance of survival. Could it be that this “survival of the fittest” instinct is surfacing in night-waking babies, rather than just a dirty diaper or an empty stomach?

But night waking in babies isn’t just about feeding, it’s also about the affection and the bond between mother and baby — which benefits the mother as well. Anthropologist Holly Dunsworth of the University of Rhode Island says that while Haig’s theory is interesting, it isn’t the only theory out there. “There are so many good juices running through infant and Mom,” shares Dunsworth. “It’s rewarding beyond the calories and hunger satiation for everyone involved. When you look at it from that perspective, waking up to feed looks more like cooperation than conflict,” she adds.

Cave moms didn’t work 9-5

Our sleep patterns changed over the (thousands of) years. When we lived as hunters and gatherers and slept in caves, our periods of sleep were shorter and more flexible. Katie Hinde, a Harvard evolutionary biologist, shared a response to Haig’s hypothesis that was published in the same journal. “The expectation that mothers and infants ‘should’ have uninterrupted, consolidated sleep is, in many ways, a historical artifact,” Hinde writes.

If your sex life feels like a historical artifact, don’t feel too bad. Regardless of the cause of all those shrill cries, Baby will only rule your sleep cycles — and obliterate your sex drive — for a relatively short period of time.

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The ultimate new baby checklist

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