Why Is It So Hard for Babies to Sleep Alone?

history of infant sleep verticle.jpeg

I remember those days like it was yesterday, sitting on the couch holding my sleeping infant with my computer propped next to me, typing a 14 page research proposal with my one free hand, my back twisted and bent for hours to reach the computer, sending pain spasms through my neck and arms. Sure, it took at least twice as long to type that way. But it also gave me an hour or two to work. If I put down that boy, he’d wake up within 5min. Holding him to sleep, I could possibly get 10 times as much done despite the physical inconvenience. What busy mom can argue with those numbers? As the primary caregiver, a teaching assistant, and a doctoral candidate all at once, it seemed I had no choice but to capitalize upon naps in whatever way possible to get the work done.

All parents hear stories (which they later will learn are little more than myth and legend) of the baby who sleeps in his crib the moment he’s out of the womb. All parents hope they will be the ones to have this child. Even if they are realistic people, they expect the child will sleep alone at least SOME of the time. Yet almost every friend, family member, and acquaintance I have known are astounded initially by their child’s near complete inability to sleep alone. “This child will ONLY sleep when he is in my arms!” They exclaim, as if their child is unique in this respect. They must not have really believed all the gentlemen and -women who entered parenthood before them, who made the same cries over their social media outlets. But as far as I have been able to tell, MOST infants have a very hard time sleeping out of arms, let alone in a room alone. (Unless they exhaust themselves crying in their car seat. Have traffic jams felt like humanitarian crises in your family? Boy am I glad that’s over.) And families who don't experience sleep challenges in the beginning can expect them to arise around 6 months after birth, when separation anxiety begins to bloom (which, to the infant, makes separation from caregivers feel akin to physical pain) (1,2).

The first step to understanding your baby is to understand what kind of life your baby is built for.”

I think new parents could save themselves a whole lot of suffering if they started out with realistic expectations for their infant. So, if you aren’t a parent yet, know this: There's a good chance your child will only sleep in-arms to start. Plan accordingly. Realistically, most parents can’t accommodate this arrangement for very long. So, let’s dive a little deeper. Why do babies have such a hard time sleeping alone, and what can we do about it?

Consider this- do you leave your baby in a room alone for extended periods of time when he’s awake? If you do, you may have noticed he doesn't like it. Babies don’t just have trouble sleeping alone, they have trouble BEING alone. The fear of being alone, the need to be physically joined with a caregiver, might be the most important instinct a human baby is born with. I don’t mean there’s nothing we can do to reach an agreement with our babes. But if we want to do something about it that is both effective and kind, we have to first understand our infants, and why they are the way they are. And the first step to understanding your baby is to understand what kind of life your baby is built for.

For more than 95% of human history we were hunter gatherers. And when I say “human history” I’m ONLY referring to the history of the most modern edition of human, Homo sapien. There were many editions of human before us, who also lived as hunter-gatherers for millions of years. That is the life for which the human baby is built. And we know a lot about hunter-gatherer life, not only from the detective work of archaeologists around the world, but also because there are a number of hunter-gatherer societies still alive today! Anthropologists have visited these current hunter-gatherers, lived with them, observed them directly, and tallied up the similarities and differences between hunter-gatherers who live in different environments around the world. Here are some things we’ve learned that are relevant to understanding our babies.

Infants don’t have to be taught how to sleep, but they DO have to be taught to sleep alone.”

Hunter-gatherers don’t put their BABIES down:

Almost ever. I mean, where would they put them? They have no beds or bassinets or playpens. Infants are carried (3) the vast majority of the time in slings and wraps, usually by the mother, but when she is indisposed the baby will be carried by other women or even children. Infants historically have had near constant body-contact (4) with a safe community member.

One reason is obviously safety. But another reason appears to be the infant’s extremely immature autonomic nervous system- the system that regulates all our bodily functions that don’t require our conscious attention (think breathing, digesting, heart rate, blood pressure regulation, and everything else you need to do to live but don’t have to think about doing). The autonomic nervous system of human infants is INCREDIBLY underdeveloped at birth (5). I mean, so underdeveloped that it's like they are still fetuses. This means our infants have trouble regulating their breathing, body temperature, heart rhythm, etc. Contact with the mother’s body (6) appears to regulate the infant’s autonomic nervous system, which probably means many infants feel dysregulated when they are not being held.

Hunter-gatherers co-sleep:

Actually ALL mammals co-sleep with their infants without exception. Well, with the exception of modern western humans. Most human cultures around the world STILL co-sleep, and infants didn’t even sleep alone even in our western culture until sometime after the industrial revolution, about 200 years ago. How does 200 years stack up against 250,000 years of Homo sapien history? It’s a slender sliver. For a visual of what 200 years means in the grand scheme of human existence, check out the image on the left.

In hunter-gatherer societies, leaving a baby to sleep alone would be a death sentence for the baby. Hunter-gatherers don’t have safe cribs in a safe room in a safe house. Everyone sleeps together, adults and children alike. What are they going to do, leave the baby alone on the periphery of the community, keeping him warm with his own personal fire? Yeah, you’ll be lucky if you see that baby again. And the baby is going to cry EXCESSIVELY until someone rescues him from his fate. In modern sleep training circles, we demonize “rescuing” the crying baby. But until a few generations ago, that’s just what parents were MEANT to do.

You might be thinking, "yeah but I made a safe and cozy nursery, there are no scorpions or wolves there, he is safe to sleep alone." Sure, but have you tried explaining that to your baby? See if he understands. Your baby can’t see 12 inches beyond his nose, how can you expect him to evaluate the safety of his environment?

Another reason infants may feel the need to sleep in arms is, again, to regulate their immature autonomic nervous systems. Many babies suffer from frequent apnea episodes while they sleep. This means they stop breathing temporarily for, often, no reason other than that their nervous system "program" isn't mature enough to keep things going consistently. Some evidence has pointed to autonomic nervous system dysregulation as a possible cause of sudden infant death syndrome (SIDS) (7,8). Infant body temperature and heart rate may be stabilized by contact with the mother’s body during sleep, and obstructive apnea reduced (9,10). Infants may sense that their bodies are dysregulated when they are not touching a caregiver, and this may be uncomfortable for them.

Hunter-gatherers breast-feed:

All hunter-gatherer infants are exclusively breastfed on demand during infancy, and breastfed for soothing up to 5 years (11,12). Hunter-gatherer women and women from developing countries do not have the breastfeeding challenges (13) that we have here in the west. In fact, women who were never pregnant, or not pregnant recently, will begin lactating to care for a child who’s lost his mother. Breastfeeding isn’t practical or possible or even desirable for many women in the developed world, and isn’t that great that we have alternatives? But breastfeeding is relevant to infant sleep because it reduces the risk of SIDS, and is supported by co-sleeping (14,15).

Your baby is built to seek nutrition, immunity, autonomic regulation, soothing, and safety from your body, just as she did in utero. In the modern world we think of birth as this huge transition, the threshold between the baby being a part of mother’s body to being independent from her body. This is false. Babies are still dependent on mama’s body after birth, and gradually gain independence from her body over the course of the first year or two (or three, or four…).

One woman once said to me that she wished someone had prepared her for the “overwhelming physicality of motherhood.” By that she meant, nursing almost constantly, never being able to put the baby down, feeling unable to even get dressed or get herself a drink due to the constant and unexpected in-arms arrangement. We have been fed so many lies about children and independence that we come into motherhood completely unprepared for this tiny being to be attached to us like a leech for so long. We feel parasitized, because we aren’t prepared. And even if we are prepared, we are unsupported.

Unsupported because no one is going to let you slow down just because you have an infant. You probably don’t even have paid maternity leave if you live in the USA. And what does that do to a new mother, to have a baby who is demanding the emotional and physical nourishment of her body, and to have no choice but to continue with business as usual? This conflict between infant’s and mother’s needs fuels the venom between attachment parents and cry-it-out parents (and everyone in between). Most mothers are faced with daily choices involving meeting her child’s needs at the expense of her own. And however she chooses to balance herself and baby on a daily basis, she is likely to feel plenty of guilt and regret. I’ve told you why your baby feels strongly about being held by you, but that information does nothing to change your reality- you probably need to get stuff done without holding your baby.

Infants don’t automatically know that their crib is safe enough to be alone in it, but we can gradually teach them it is safe. Infants don’t automatically know that when you leave the room, you are still available to them if they need you. But we can build their faith that this is so.”

There are ways to approach infant sleep gently. Here are a few things you might consider to help get through the first months/year. I think there is a solution here for nearly every kind of mother. Which option is right for you may also depend largely on who your baby is. Some babies can be coaxed more easily than others into independent sleep. A child who is stubborn or very good at expressing her wants and needs may sway you to change your lifestyle more than an easy-going child, who might be more compliant with your suggestions.

(1)  Change of pace: A woman may need to slow down more than she expected she would once she has given birth. I would argue ALL mothers should consider doing this as much as possible. Some women really can’t slow down, but some women just FEEL like they can’t because they’ve been caught up so long in a rat race, competing with men who don’t feel the same tug between parenting and work. But I propose you see your reproductive biology as an advantage rather than a disadvantage. Lots of research is flowing in showing that stress shortens a person’s life, massively increasing the risk of chronic disease (16,17). Your baby may actually be protecting you and your health by forcing you to slow down. In many cases, a woman might find that she won’t lose everything if she gives herself a little time with her infant, or changes direction towards a more forgiving career. 

(2)  Alter expectations: A mother may want to contrast and compare options she hadn’t previously considered, such as room or bed-sharing. Alternative sleep arrangements solve sleep-related problems for some parents. For example, breastfeeding mothers who co-sleep get more sleep (18) than those who don't co-sleep, on average. I have to add a safety note here: the American Academy of Pediatrics doesn’t recommend bed-sharing until more research on safety and safe practices is available (19). They DO recommend room-sharing for at least 6 months to reduce the risk of sleep related infant deaths. If you choose to bed-share rather than room-share, see these safe bed-sharing practices (20), and understand that though emotional benefits have been associated with bed-sharing (21,22), we can't yet quantify the risk involved.

(3)  Cultivate independent infant sleep habits: This gentle approach requires a consistent and mindful execution over the course of many months. Give baby a few weeks to adjust to being on the outside (indulging her, feeding to sleep in-arms). Then start gradually introducing alternative soothing methods (23) other than feeding, and try putting her down drowsy but awake sometimes. After your infant has accepted a diversity of soothing-to-sleep methods, you can try soothing her without picking her up (24). This is NOT the same as letting your baby cry-it-out, because you are not leaving her to cry, unattended, for prolonged periods of time. Using these methods, you are responding to her AND gently encouraging independent sleep skills as your baby becomes ready for them. You are also giving her a diversity of tools to use to get to sleep, so as you begin removing some of these tools when she is older (like breastfeeding), she will still have other tools that work for her (falling asleep to the sound of your voice). Note: a baby should not be encouraged to sleep through the night until she is at least 6 months old. Babies younger than this usually require calories at night for good nutrition, and are at risk for SIDS if they are encouraged to sleep too deeply for too long (25,26).

(4)  Sleep Science: Work with your infant’s sleep biology instead of against it by putting him to sleep when he is most primed for sleep. This will help him sleep deeply enough to lose track of you. This means becoming aware of your infant’s sleep window (avoiding putting him down under- or over-tired) (27), sleep cues (28), and understanding his sleep cycles and how they change over the course of his first year. There’s more to this than I can write in this piece, but the links will give you a place to start your research. Also, reducing daytime stress and promoting feelings of security during the day will calm his hypothalamic-pituitary-adrenal axis (the stress system), reducing nighttime wakings and parasomnias (29). 

(5)  Hire a sleep expert: There’s a lot more to infant sleep science than what I have space for here. You can find it all online, but if you’re exhausted it’s probably better to just hire someone who’s already done the research, and can also support and coach you. Be sure to hire a sleep consultant who has similar parenting attitudes as you do, or who can work with a diversity of parenting styles. Usually, cry-it-out methods introduce unnecessary stress to parents and children, and gentler methods work just as well (30).  There are a growing number of sleep consultants who have the training to help babies of all ages sleep independently without a lot of crying. These consultants take infant biology, emotional wellbeing, and physical wellbeing into consideration (*ahem* shameless plug- see my services). Be wary of anyone who claims to have a method that works for all babies. NOTHING works for all babies, or all families, so any expert has to have a bag of tricks, not one trick.

Infants are struggling to navigate the mismatch between their genetic makeup and the modern world. Parents are struggling to balance work and parenting without the support of a village.”

To Summarize

Parents should expect independent infant sleep to be a challenge. We have to respect infant rebellion against independence as a strategy that, until very recently, improved all our chances of surviving infancy. You can’t expect all that history to be erased overnight. That said, the world is what it is. Can we attend to infants the way hunter-gatherers do? No, most of us can’t.

Do babies really have to be taught to sleep? After all, hunter-gatherers don’t report any infant or child sleep challenges in their villages (31,32,33). Infants don’t have to be taught how to sleep, but they DO have to be taught to sleep alone. Infants don’t automatically know that their crib is safe enough to be alone in it, but we can gradually teach them it is. Infants don’t automatically know that when you leave the room, you are still available to them if they need you. But we can build their faith that this is so. We can’t expect an infant to be alone for many hours while awake, but over the course of the first year we can gradually teach him to feel cozy in a crib and confident that his parents are protecting him just at the other end of the baby monitor. This education goes a long way to facilitating independent infant sleep.

In our modern culture, both parents often have jobs with inflexible schedules that are unaccommodating to the irregular and constant needs of their infants. This situation is unnatural for infants AND for parents, putting stress on everyone. Parents may feel like they are at war with their infants when it comes to sleep. They get angry at their baby for giving them so much trouble. Meanwhile attachment parents retaliate on the infant’s behalf. I recommend a more tempered approach that involves compassion for both infants and parents. Infants are struggling to navigate the mismatch between their genetic makeup and the modern world. Parents are struggling to balance work and parenting without the support of a village. This can lead to burnout and depression. A better understanding of our needs, our infant’s needs, and the way modern life is interfering with both, will enable us to find more effective and less stressful ways to help our infants adjust to the realities of our world.


(1) Szalavitz, Maia. “In the Brain, Broken Hearts Hurt Like Broken Bones.” Time Feb 27, 2012. Web. Retrieved on April 2, 2018 from http://healthland.time.com/2012/02/27/in-the-brain-broken-hearts-hurt-like-broken-bones/

(2) Panksepp J. Affective neuroscience of the emotional BrainMind: evolutionary perspectives and implications for understanding depression. Dialogues in Clinical Neuroscience 12.4 (2010): 533-545.

(3) University of Notre Dame. "Child rearing practices of distant ancestors foster morality, compassion in kids." ScienceDaily. ScienceDaily, 22 September 2010. www.sciencedaily.com/releases/2010/09/100921163709.htm

(4) Narvaez D, Tracy Gleason, Lijuan Wang, Jeff Brooks, Jennifer Burke Lefever, Ying Cheng, the Centers for the Prevention of Child Neglect. “The evolved development niche: Longitudinal effects of caregiving practices on early childhood psychosocial development.” Early Childhood Research Quarterly 28.4 (2013): 759-773.

(5) Wittman, Anna Blackburn, L Lewis Wall. “The evolutionary origins of obstructed labor: Bipedalism, encephalization, and the human obstetric dilemma.” Obstetrical and Gynecological Survey 62.11 (2007): 739-748.

(6) Feldman, R, Al Eidelman. “Skin-to-skin contact (Kangaroo Care) accelerates autonomic and neurobehavioral development in preterm infants.” Developmental Medicine and Child Neurology 45.4 (2003): 274-281.

(7) Weese-Mayer, Debra E, Elizabeth M Berry-Kravis, Lili Zhou, Brion S Maher, Mark E Curran, Jean M Silvestri, Mary L Marazita. “Sudden infant death syndrome: Case-control frequency differences at genes pertinent to early autonomic nervous system embryologic development.” Pediatric Research 56 (2004):391-395.

(8) Lucchini, M, MG Signorini, WP Fifer, R Sahni. “Novel heart rate parameters for the assessment of autonomic nervous system function in premature infants.” Physiological Measures 37.9 (2016): 1436-1446.

(9) McKenna, James J, Thomas McDade. “Why babies should never sleep alone: A review of the co-sleeping controversy in relation to SIDS, bedsharing and breastfeeding.” Paediatric Respiratory Reviews 6.2 (2005): 134-152.

(10) Richard, Christopher A, Sarah S Mosko, James J McKenna. “Apnea and periodic breathing in bed-sharing and solitary sleeping infants.” Journal of Applied Physiology 84.4 (1998): 1374-1380.

(11) Dewar, Gwen. [Web log] (Feb 2014). Breastfeeding on demand: A cross-cultural perspective. Retrieved on Feb 19, 2018 from Parenting Science (https://www.parentingscience.com/breastfeeding-on-demand.html)

(12) Palmer, Brian. [Web log] N.d. Breast-Feeding in Prehistoric Times: Did cave-babies have attachment parents? Retrieved on Feb 19, 2018 from Slate (http://www.slate.com/articles/news_and_politics/explainer/2012/05/time_magazine_breast_feeding_cover_how_nursing_worked_in_prehistoric_times_.html)

(13) Gribble, Karleen D. “The influence of context on the success of adoptive breastfeeding: developing countries and the west.” Breastfeeding Reviews 12.1 (2004): 5-13.

(14) Jenco, Melissa. [Web News Article] (October 2017). Study: Breastfeeding for at least 2 months decreases risk of SIDS. Retrieved on Feb 19, 2018 from American Academy of Pediatrics News http://www.aappublications.org/news/2017/10/30/BreastfeedingSIDS103017

(15) Australian Breastfeeding Association. [Web Article] (Aug 2017). Breastfeeding and Co-sleeping.  Retrieved on Feb 19, 2018 from https://www.breastfeeding.asn.au/bfinfo/breastfeeding-and-co-sleeping

(16) TED (April, 2017). The Science of Cells That Never Get Old [Video file]. Retrieved on Feb 19, 2018 from https://www.ted.com/talks/elizabeth_blackburn_the_science_of_cells_that_never_get_old

(17) SCSASmithers (March 2013). When the Body Says No—Caring for Ourselves While Caring for Others. Dr. Gabor Mate [video file]. Retrieved on Feb 19, 2018 from YouTube https://www.youtube.com/watch?v=c6IL8WVyMMs&list=PL8xp_1cOczE21WxHU9QveJitfs8Pzzvqu&index=3

(18) Quillin, IM, L Lee Glenn. “Interaction between feeding method and co-sleeping on maternal-newborn sleep.” Journal of Obstetric, Gynecologic and Neonatal Nursing 33.5 (2004): 580-588.

(19) SIDS and Other Sleep-Related Infant Deaths: Evidence Base for 2016 Updated Recommendations for a Safe Infant Sleeping Environment. Rachel Y. Moon, TASK FORCE ON SUDDEN INFANT DEATH SYNDROME Pediatrics Nov2016, 138 (5) e20162940; DOI: 10.1542/peds.2016-2940

(20) McKenna, James. [Web article]. N.d. “Save Cosleeping Guidelines.” Retrieved on Feb 19 2018 from the Mother-Baby Behavioral Sleep Laboratory, University of Notre Dame (https://cosleeping.nd.edu/safe-co-sleeping-guidelines/)

(21) Keller, Meret A, Wendy A Goldberg. “Co-sleeping: Help or hindrance for young children’s independence?” Infant and Child Development 13.5 (2004): 369-388.

(22) Waynforth, D. “The influence of parent-infant cosleeping, nursing, and childcare on cortisol and SIgA immunity in a sample of British children.” Developmental Psychobiology 49.6 (2007): 640-648.

(23) Karp, Harvey [web log]. N.d. The 5 S’s for Soothing Babies. Retrieved on Feb 19, 2018 from Happiest Baby https://www.happiestbaby.com/blogs/baby/the-5-s-s-for-soothing-babies

(24) My Baby Sleep Guide [web log]. N.d. Shush-Pat. Retrieved on Feb 19, 2018 from http://www.mybabysleepguide.com/2009/01/shhpat.html

(25) Sheehan, Jan [web article]. N.d. New Ways to Reduce the Risk of SIDS. Retrieved on Feb 19, 2018 from Parents (https://www.parents.com/baby/health/sids/new-ways-to-reduce-the-risk-of-sids/)

(26) Harper, Ronald, B Leake, Howard Hoffman, DO Walter, Toke Hoppenbrouwers, JE Hodgman, MB Sterman. “Periodicity of sleep states is altered in infants at risk for the SIDS.” Science 213.4511 (1981): 1030-1032.

(27) GoodNight Sleep Coaching [web log]. N.d. Sleep Windows- What You Need to Know. Retrieved on Feb 19, 2018 from https://www.goodnightsleepcoaching.com/2018/02/13/sleep-windows-what-you-need-to-know/

(28) My Baby Sleep Guide [web log]. N.d. Sleep Cues. Retrieved on April 2, 2018 from http://www.mybabysleepguide.com/2009/01/sleepy-signs.html

(29) Curran, Oisin [web article]. N.d. How Night Terrors Work. Retrieved on Feb 19, 2018 from How Stuff Works (https://health.howstuffworks.com/mental-health/sleep/disorders/night-terrors1.htm)

(30) Dewar, Gwen [web log]. (Jan 2016). Gentle Infant Sleep Training. Retrieved on Feb 19, 2018 from Parenting Science (https://www.parentingscience.com/infant-sleep-training.html)

(31) Dewar, Gwen [web log]. N.d. Infant Sleep Problems: A Troubleshooting Guide. Retrieved on Feb 19, 2018 from Parenting Science (https://www.parentingscience.com/infant-sleep-problems.html)

(32) Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM.2015. Natural sleep and its seasonal variations in three pre-industrial societies. Curr Biol. 25(21):2862-8. 

(33) Samson DR, Crittenden AN, Mabulla IA, Mabulla AZ, Nunn CL. 2017. Hadza sleep biology: Evidence for flexible sleep-wake patterns in hunter-gatherers. Am J Phys Anthropol. 162(3):573-582.

©Sarah Dean, PhD