Training for Sleep Training: Evolution Is Spelled P-R-O-X-I-M-I-T-Y - Blog

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Training for Sleep Training: Evolution Is Spelled P-R-O-X-I-M-I-T-Y

Published Date: 04/29/19

If you’ve ever had the privilege to see a monkey – of any species – holding her baby with your own two eyes, you know two things. 1) People really and truly go crazy for monkeys and 2) they look suspiciously familiar (damn, those babies are cute). If you don’t know WHY they look familiar, you may want check out the internet real quick and come back. Inevitably, we watch these apes breastfeeding and co-sleeping with their hairy, scrawny babes with such love and admiration. “Aren’t they sweet?” we coo. “How lovely!” we exclaim.


We share 98.7% of our DNA with chimpanzees (and bonobos, too). They are our closest living relatives!
That’s why this guy looks like your Uncle Bob.
Photo by Rishi Ragunathan on Unsplash

And, yet, when we see or hear of a human mama doing the same, our tone changes. “Aren’t they a bit old for that?” we question. “You’re letting them manipulate you!” we caution. Suddenly, what’s biologically normal for every other species is problematic when it comes to humans. Why the double standard?

Here’s my secret to you: It’s always been biologically adaptive for mammals (that’s us, guys!) to co-sleep with their infants. This is not the story of what constitutes safe bedsharing. For that, you can look here. This IS the story of why your little nugget won’t nap anywhere but on you. Why, try as you might, you can’t get him into his own bedroom. Settle in, mamas. Let’s chat.

Newborns are beautiful. Precious. Miraculous. But, by golly, are they useless. Newborn horses can walk within an hour after birth. A newborn baboon can cling to its mother’s fur as she literally swings through the trees. The blue wildebeest can walk within SIX MINUTES of birth and outrun a hyena within a day. Our babies? Can’t even hold up their own dang head. For like, an unreasonably long time.

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I know I’m being harsh. After all, we’ve evolved to have some pretty cool reflexes to help make up for this complete ineptitude. But I’m being harsh because it *matters*. Even those species sleep closely with their newborns, and those newborns can physically run from danger if needed. This prolonged period of helplessness means that our babies have to rely on being able to elicit caregiver protection and care. Babies wake frequently in the night and cry or root in order to increase parent proximity and this, in turn, means the baby has adequate safety, nutrition, and immunological protection (McKenna, Ball, & Gettler, 2007).

Expecting a human infant to sleep alone (and well, I might add) is as preposterous as asking that fish to climb a tree.
An infant can no sooner become physiologically independent than a fish can grow opposable thumbs and the ability to breathe out of water.

Evolutionarily speaking, you wouldn’t want a helpless newborn separated from its parents. Having the child nearby decreases the chance of child predation (Gettler & McKenna, 2011). Furthermore, proximity to their infant during the night increases maternal sensitivity to infant distress, which increases the chance mama could intervene quickly in a life-threatening situation, potentially before that baby wails and invites the tawny, scrawny lion over for a visit (Mosko & McKenna, 1997). If a baby woke and was hungry or wet or scared or just feeling sassy and he needed to cry to get mama’s attention, guess who’s coming to dinner? Any predator within earshot.

Think about it. If you were camping in the wilderness with your partner and woke up feeling hungry, would you just start yelling at them to give you a burger? No. Why? Probably because there are no burgers. But, also, because that’s a pretty sure way to alert predators to your location. However, if some food were right next to your mouth when you woke up, you could quietly and safely nibble away.

Because spiders, guys. Also bears. But mostly spiders.

From a contemporary standpoint, we know a lot about some other nifty things sleeping with your babe does. Bedsharing, more specifically, regulates infant body temperature and helps to regulate infant heart rate, and proximity to the mother’s face stimulates breathing (McKenna, Mosko, Drummond, Hunt, & Arpaia, 1994). Furthermore, we know that, for infants, sleeping alone in a separate room increases the risk of SIDS (Mitchell and Thompson 1995Blair et al., 1999Carpenter et al., 2004). On the flip side, when an infant sleeps in the same room as mom, the risk of SIDS drops by 50% (Blair et al., 1999, Carpenter et al., 2004).

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Co-sleeping has, historically, meant that babies who were fed on demand, usually in the side-lying breastfeeding position, were more likely to survive. Therefore, this evolved to be the biologically normal, species-typical behavior. In fact, we see co-sleeping in *all* primates, and 95% of cultures around the world do it. And in countries where co-sleeping rates are higher, the rate of infant mortality is lower.

Why does evolutionary history matter? First, because we don’t evolve terribly quickly. For all our smart phones and same-day delivery options, we are not as evolved as we’d like to think. And, second, evolution, by definition, selects only features that help us to survive. Infants have evolved to be perfectly adapted to one particular microenvironment: their mother. Every single behavior an infant displays only makes sense when you look at its function: to interact with his mama. Involuntary head turn when you touch his cheek? Weird. Unless you realize it allows him to find the breast. His arms fly out when there’s a loud noise? Bizarro. Unless you appreciate how that helps him hold onto mom when he feels threatened.  Waking frequently and crying in the night? Odd. Unless you understand that it promotes closeness to his most precious mama.

Infants are not ready to respond to or interact with the larger environment without mama as a safeguard. Mama is all they know. Before birth, they knew nothing of cold, discomfort, pain, hunger, or incessant cooing from doting great aunts. We push and push for infants to be physiologically independent and able to navigate this brave new world, even when the evidence tells us they are utterly incapable of doing so.

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Infants have a biological need for contact with their mothers. Using social or cultural reasoning for separating mothers and infants at night is, therefore, necessarily inadequate. Quite frankly, my dear, it’s a bit arrogant of us, as a society, to decide that infants have evolved past these needs simply because we want them to. On brand, perhaps, but arrogant. We’ve created a caregiving culture for which our infants are not biologically designed (McKenna et al., 2007).

Expecting a human infant to sleep alone (and well, I might add) is as preposterous as asking that fish to climb a tree.
An infant can no sooner become physiologically independent than a fish can grow opposable thumbs and the ability to breathe out of water.

You know what? Even if you ignore everything I said above, you sleep better with someone nearby. Yes, you.  You are vulnerable when you sleep. Humans are vulnerable when they sleep. We have no thick hide, no protective shell. Sleeping with others assures us of safety and, in the absence of other humans, we substitute with locked doors and security systems. Babies – those adorable little lumps – feel even more vulnerable because they ARE. Plus, they haven’t had the time to research the pros and cons of security cameras vs. motion sensors.

history of sleep training

So, mamas, next time someone asks you if your sweet babe is sleeping through the night yet, simply respond “we haven’t evolved past that yet”.

Stay tuned for the next installment on what we know about infant sleep and sleep training!

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About the Author
Amana Cannarella has a P.h.D in Applied Developmental and Educational Psychology. Through her business Be.loved, she provides full-spectrum and full-service support to expecting, new, and growing families. She can be reached at [email protected].