Do Babies Cry At Night To Prevent Younger Siblings?
Exhausted parents often ponder why babies cry at night and seem to have a reversed internal clock. One study claims that the night-time needs of an infant are a birth control mechanism on the part of the baby. Certainly, the study didn’t imply that babies cry at night to deliberately prevent their mothers from conceiving future children, but the study did imply that it is an evolutionary survival mechanism that we are stuck with for now.
Besides for drawing their mothers’ attention away from their mates and utterly exhausting the early human mothers, nighttime crying acted as a birth control in another way. The hypothesis is that waking up crying at night is an adaptation of human infants in a biological attempt to force their mothers’ lack of menstruation. While not 100 percent effective, nursing at night does offer a woman some birth control for several months. Still, merely feeding at night and altering mom’s hormones weren’t ever quite enough to prevent future siblings for very long, so the babies that started crying more at night, right around six-months-old, were more likely to survive, the study says. If they survived, they were more likely to pass along the crying at night trait. The babies that were our ancient ancestors happened to be bigger “cry-babies” at six-months-old than the babies that didn’t survive to populate the earth.
David Haig explained in the journal Evolution, Medicine and Public Health that a younger sibling would mean sharing the parents’ attention. Babies that cried more at night as we evolved as a species were more likely to be guaranteed their parents less divided attention, and therefore, were more likely to survive. Haig built up his theory by looking at particular genetic disorders. Science News explained that from these disorders Haig was able to learn that, “Babies who get certain genes from their mothers sleep longer in the night, which is in the best interests of a woman who wants to get pregnant again. But babies who get the same genes from their fathers wake up more often, delaying ovulation in their mothers.” When you consider that fathers have no guarantee that the next baby will also be his, their genetics might have evolved to not be as concerned with future offspring. The fathers’ genetics would want what is in the best interest of their children’s survival, Haig believes. He added that on the flip side, “Mothers have evolved to maximize their numbers of surviving children, which is different from maximizing the survival of each individual child.”
Anthropologist James McKenna of the University of Notre Dame isn’t so sure about this theory that babies cry at night to prevent future siblings. McKenna and his colleagues on one study found that 40 percent of babies awoke crying at night because of the mothers moving about. These babies would have plenty of benefits from waking up with their mothers besides birth control. Babies who wake up crying at night would have the benefit of being snuggled, tended to and even something more significant.Babies that are easily awoken by a mother’s wakefulness would be prevented from falling too deeply into sleep, which can be dangerous, McKenna said, proposing an alternate reason why babies might cry more at night.
[Photo by tostadophoto.com]
