Why Bed-sharing Is Healthy and Sleep Training Is Child Abuse, According to a Biological Anthropologist

Co-sleeping has developmental for infants, says James McKenna, a leading expert on the subject. And while sleep training may make things easier for parents, it's not what babies need

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"I’m aware of the difficulties piled on the shoulders of parents," says McKenna. "...But I’m not sure that the changes of the modern world should be loaded onto the narrow shoulders of the infant."
"I’m aware of the difficulties piled on the shoulders of parents," says McKenna. "...But I’m not sure that the changes of the modern world should be loaded onto the narrow shoulders of the infant." Credit: Anchiy / Getty Images
Einat Talmon

“Exaggerated attention to the child, excessive concern about caring for and nurturing him – [this has a] harmful influence on his psychic development. The result, already in the first months, is a capricious, restless infant who upsets the whole family.”

– “Your Child from Birth to Puberty: A New Guide for the Young Mother” (Hebrew, 1973)

Those unbelievable words were written by A. Fructer Peri the year I was born. He was not alone. The psychologist John Watson, who’s considered the father of behaviorism, viewed maternal love as a dangerous instrument; and the physician Richard Ferber forged a whole career out of transforming children’s sleep into a “problem” that requires a solution. All were members of the prestigious club – among whom were also numbered Sigmund Freud and the American pediatrician L. Emmett Holt – of authors of books that educated parents about the right way to raise obedient, unspoiled children.

“Those who laid the foundations for caring and educating children in the 20th century are a handful of white men who probably never changed a diaper in their lives,” says James McKenna – and immediately grasps the irony of that judgment. For McKenna, too, is a white man of the old school, the flesh and blood of the American academic establishment. He “pleads guilty” even before this is pointed out to him, flashing a charming smile that will punctuate our Zoom conversation frequently.

Prof. McKenna, a biological anthropologist with an array of awards to his name, is regarded as an international authority on infant sleep and crib death. In the laboratory he established at the University of Notre Dame, in Indiana, he spent years studying how the sleep environment of mothers and infants affects babies’ development and their physical and mental condition. In this lab, the first of its type in the world, mothers and infants share the same bed, while researchers monitor various parameters.

Drawing on unrivaled experience, McKenna, speaking from his current home, in California, allows himself to level fierce criticism at the people who formulated the principles of parenthood on which millions of children were raised in the West, and which still serve as a beacon to many. According to him, babies should sleep next to their parents.

Co-sleeping, as it is called, can take different forms, McKenna notes. Many Israeli parents practice one version, in which the infant sleeps in a crib that lacks a fourth side, abutting the parents’ bed. But there are other forms, too. In some cases the parents share a bed with the infant, sometimes only one parent sleeps with the infant, in other cases the whole family sleeps together in the same room. Sleeping in the same room with an infant in a separate bed is also considered co-sleeping, and McKenna is convinced it has many advantages. In general, the deeper the physical proximity, the deeper the advantages.

“The views of those physicians about the right way to raise children were never based on research studies,” McKenna says. “They were based on their moral and folk beliefs. They believed in a package deal, which includes baby formula, which was thought to be superior to human milk, the perceived need to produce independent and secure infants through enforced nighttime separation, and protecting the couple’s relationship, which had the highest priority. Western ‘science’ in regard to infants’ sleep and nutrition is, at its base, the product of the values and ideologies of the culture that created them.”

Indeed, parents in the West often feel that they will be judged and reprimanded if they act contrary to the norms by which they were educated, even if those norms sometimes conflict with their gut feelings. In his lectures, the Spanish pediatrician Carlos Gonzalez frequently quotes a survey that was conducted in his country in which most of the parents who were asked whether they co-sleep with their infant offspring replied in the negative. But to the follow-up question – “What about last night?” – the number of positive replies surged.

Similar findings were recorded in a British study conducted by Helen Ball, an infant sleep expert. She asked women who were about to give birth whether they intended to co-sleep with their baby, and found that not one intended to do that. Three months after giving birth they were asked the same question again – and it turned out that 70 percent of them were co-sleeping with their babies at least some of the time.

So, if most parents do it, could it be that it’s the natural thing to do?

Starting with primates

James McKenna, 72, was born in Boston. He did not acquire his knowledge from observing mothers in primitive tribes. As a novice anthropologist, he studied patterns of socialization, attachment and parenting among monkeys and apes. He examined the negative effects of separating offspring from their mothers, even short-term, and took a particular interest in such physiological parameters as heart rate, respiration, temperature, immune system, cortisol level, digestion and growth.

When his first (and only) child was born, in 1978, McKenna decided to apply what he had learned to humans. In 1983, he joined the neurology department of the University of California, Irvine, where he conducted his first experiments. The studies examined whether bed-sharing combined with breastfeeding contributed to the regulation of all those parameters, as compared with infants who sleep alone.

The difference between McKenna and many of the scientists who preceded him is already found in the basic research premise with which he launched his studies. The earliest studies on babies’ sleep were conducted in the 1950s, a period in which breastfeeding rates in the U.S. stood at only 9 percent. As a result, those early studies were based on the model of an infant who slept alone and was fed baby formula. McKenna, on the other hand, recruits millions of years of evolution (“which tells a good story”), and bases his research on it. In his approach, the basic research unit in studying infant sleep is not the child alone, but the child and his or her mother. He is aware that using evolution as his point of departure doesn’t spare him from harboring biases, but he’s convinced that it is a good starting point for posing the necessary question – “Who is the human infant?” – which precedes the question, “What should we do with the infant?”

Who, then, is the human infant?

“To know the human infant, we need to be aware that infants are driven by needs alone: They have no desires; they are guided by instincts and reflexes. At birth, the human is the least neurologically mature of all primates, and the most reliant on physiological regulation by the caregiver for the longest period of time. What this means is that the child’s physiological system is incapable of functioning optimally without being in contact with the mother’s body, which continues to regulate the infant, even after it has left the womb. In other words, the mother’s body is the habitat, the environment to which the human infant adjusts.

“Whether they are born in Brazil, Sweden, the United States, England or Nepal, whether living in a hunting-gathering society or an industrialized city: When they are resting on their mother’s torsos, both premature and full-term infants breathe more regularly, use energy more efficiently, maintain lower blood pressure, grow faster and experience less stress.

I see a whole school that the baby’s brain experiences at night, thanks to the celebration of sensual interaction of co-sleeping. The infant’s brain cells respond to every random contact.


“Culture, by way of values and ideologies, changes much faster than does human infant biology, and infants are compelled to pay the price of the disparity,” McKenna adds. “Their world hasn’t changed. They are completely indifferent to cultural aspects. Understanding that fact will help us understand that we can’t ‘punish’ or ‘judge’ them for not being capable of bridging that gap. That is the deepest understanding. It is precisely the recognition of the biological common denominator – before we begin to become acquainted with the personality of our own offspring – that opens the door to responding to their needs and to providing a safe and beneficent environment for them. That environment is needed for the proper neurobiological development of a newborn who starts life with a brain that’s 25 percent the volume of a mature brain and is supposed to double in size during the first year.”

McKenna illustrates this by means of an experiment conducted by the American research psychologist Evelyn B. Thoman more than 25 years ago. She and her team placed teddy bears in the incubators of premature infants, and inserted into them a pump that imitated the inhaling and exhaling patterns of deep sleep. Gradually the pace of the infants’ breathing synched with that of the teddy bear machine. This helped them regulate their breathing, and the beneficent effect continued even after they were discharged from the hospital. The teddy bears also enhanced the preemies’ neurobehavioral development – they responded to their soft presence and “cuddled” with them.

“The mother is in effect the human sleep teddy of her baby,” McKenna says. “When my son was born, I discovered I could manipulate his breathing by changing the speed of my breath, as if we had to be in sync with each other. My research later confirmed that the breathing of the mother and infant are regulated by each other’s presence – the sounds of inhalation and exhalation, the rising and falling of the chest, and the carbon dioxide that is being exhaled by one is inhaled by the other, expediting the next breath. I call the mother the ‘architect’ of the sleep of the two of them; through her sleep she determines the structure of the infant’s sleep.

“When you look at a picture of a mother and an infant co-sleeping, nothing seems to be happening, but in fact everything is happening,” he continues. “I see a whole school that the baby’s brain experiences at night, thanks to the celebration of sensual interaction that is taking place. The infant’s brain cells respond to every random contact between them. The body temperature of an infant sleeping next to its mother is higher by one degree to one-and-a-half degree than that of babies sleeping alone.

“When I’m asked whether that is the desirable situation, I reply that because infants slept next to their mothers from the dawn of humanity, it’s reasonable to think that this is the desirable temperature, so any temperature that’s lower than that should be perceived as the less desirable situation, and not vice versa. For much of the time, the sleep stages of mother and baby are in synchrony. Effectively, their sleep is intertwined. The mother is capable of pulling herself quickly out of a deep-sleep situation in the case of every change or indication that could develop into distress.”

To reduce the danger of sudden infant death syndrome (SIDS, also called crib death), the international health organizations, as well as the Israeli Health Ministry, recommend that the infant sleep in the parents’ bedroom, but not in the same bed.

A baby co-sleeping with a teddy bear in Evelyn B. Thoman's experiment.

“Those recommendations are welcome, but they relate mostly just to the aspect of the danger of death and the importance of being in the same space as the infant, so that the parent can respond immediately to unusual distress. They miss out on the rest of the beneficent aspects of co-sleeping with the infant, the ones I have devoted my life to studying. The Academy of Breastfeeding Medicine, for example, has come a long way on this issue. Its updated protocol from 2019, of which I am one of the authors, finally notes that infant sleep is culture-dependent, and calls for an end to the stigma attached to bed sharing.

“SIDS death was considered a mysterious phenomenon in the past,” he adds, “but today we know that it is not as mysterious as had been thought. For years we were instructed to put babies in their own rooms, and by doing so not only did we deprive them of all the advantages of proximity to mothers – we also caused a decline in breastfeeding rates, though breastfeeding itself reduces the risk of crib death. It reduces risk even in a less known, additional aspect: After breastfeeding, the most natural posture for putting the infant to sleep is a supine position. With the falloff in breastfeeding, infants began being placed on prone position. Sleep is deeper in that position, and an infant who gets into distress with its breathing isn’t able to wake up and thus rescue itself. And by the way, I distinguish between being placed in prone position on a mattress, and ventral-ventral mother-infant contact, which is not an example of unsafe sleep.”

In any event, according to McKenna, a discourse that is restricted to preventing the danger of crib death alone sends a message to parents that they themselves are a potential danger to their children. Is the mother’s (or father’s) sleeping body a lethal weapon, from which infants need protection? Pointedly, as is his custom, he formulates a question that turns the issue upside down: Instead of asking what parents are liable to do to their infants with their bodies, we should ask what we can do by means of our bodies for them.

This subject has even reached the courts. You have been recruited many times as an expert witness to testify that a parent who co-sleeps with their child is not endangering that child?

“I have testified in a number of trials. One that I remember well was a case in which a father who had drunk himself into a stupor fell asleep with his baby son on the sofa and caused his death. The indictment referred to the very fact of co-sleeping with the infant, irrespective of the parent’s state of consciousness or the place they were sleeping. Before I acceded to the request of the defense, I made very certain that there would be no implication that I was going to validate sleeping with an infant in a state of drunkenness. My motivation was precisely to underscore the difference between things: to make it clear that co-sleeping with an infant in a state of inebriation is dangerous and illegitimate, as compared to other situations in which co-sleeping is safe and legitimate. I did it in order to prevent the creation of a dangerous legal precedent stating that a parent co-sleeping with their baby is dangerous as such. My opinion was accepted and the original indictment was amended.”

McKenna recalls another time he testified, in the case of a couple who were in divorce proceedings. “The mother was mentally unsound, so the father had been awarded custody of their three children,” he relates. “In order to gain custody of the children [for herself], she accused him of sexually abusing the children in co-sleep. I presented an opinion about the legitimate right of a father to co-sleep with his children. Of course there are cases of sexual abuse, but co-sleeping with children – including by fathers – is not in itself such abuse.”

Instead of asking what parents are liable to do to their infants with their bodies, we should ask what we can do by means of our bodies for them.


Your studies show that not only is it a legitimate right, but that close contact with the father is important.

“Definitely. Much has been said about the ability of fathers to secrete oxytocin, the ‘love hormone,’ a subject being studied by my colleague Prof. Ruth Feldman. I examined the connection between co-sleeping and testosterone. High levels of the hormone testosterone are linked to risk-taking and rash behavior, which aren’t desirable in a period of raising offspring. Studies of human males suggest that fathers who provide childcare often have lower testosterone levels than uninvolved fathers, but no studies to date had evaluated how nighttime sleep proximity between fathers and their offspring may affect testosterone. In a study we conducted on young fathers in the Philippines, we checked for the first time the connection between testosterone levels and co-sleeping with an infant. We found lower levels of the hormone in saliva samples of fathers who bed-shared with their infant children, as compared to fathers who slept separate from their babies. What we learned from this study is that the father’s physiology is capable of adapting itself to the needs of childcare on his part.”

Even so, in most cases it’s mothers who co-sleep with the infant, and breastfeeding dictates the sleep patterns. You coined a term that combines the two: “breastsleeping.”

“I will tell you a story. That term came to me in a dream on the night before a guest lecture to the Australian Breastfeeding Association. I immediately wrote it down in order not to forget, and the next day I made it public for the first time in my lecture, and it was enthusiastically received.

“I see twice as many episodes of breastfeeding while co-sleeping, as compared to breastfeeding mothers who do not co-sleep with their babies. And even though they breastfeed more, when they are asked how many times they breastfed during the night, the answer mothers give is far less than what is the actual case. In other words, they breastfed when they were not in a completely awake state, which means they were able to rest. Sixty-five percent of those questioned who co-slept with their infant said they had had a good or satisfying sleep, compared to 40 percent of breastfeeding mothers who slept apart from their baby. In sum, co-sleeping with the infant created a cascade of related changes in terms of both the behavior and the physiology of mother and infant.”

That’s all well and good if we’re only talking about the needs of infants, but we also need to understand the parents who are frazzled from lack of sleep. Mothers who are expected to function in a competitive labor market need sleep. That need is filled by behavioral sleep intervention with the infant, known as “sleep training.”

“I approach this with humility, because I didn’t breastfeed, obviously. Still, I co-slept with my son. I am aware of the difficulties that are piled on the shoulders of parents in a dynamic world that creates stressful situations. But I’m not sure that the changes of the dynamic, modern world should be loaded onto the narrow shoulders of the infant. I only tried one time to ‘train’ my son to sleep, when I put him in the crib and let him cry. I snapped after about 10 minutes, took him in my arms and vowed: Never again. To this day – and he’s 42 – I feel guilty about it. I know that what I have to say will not be pleasant to the ear, but in my view, the practice of sleep training is absolutely child abuse. It’s a practice that’s based on a totally mistaken myth to the effect that infants have ‘a problem’ and that uninterrupted sleep is ‘good’ for them. Let’s be precise: It may make things easier for parents, and that’s understandable in our demanding world, but it is definitely not what babies need.”

James McKenna.

Nevertheless, the physical and mental exhaustion parents experience is making sleep training increasingly popular. Advocates of this form of behavioral intervention maintain that being able to fall asleep independently is an important skill that parents can impart to infants and that it can assist in cognitive development and in improving the functioning of the immune system. In addition, they argue, continuous sleep also has an influence on emotional and social development.

As a lactation consultant who in the course of my work with mothers in Israel deals with issues relating to the sleep of breastfeeding infants, I have read a number of the studies on which these arguments are based. Some of the research deals with the importance of high-quality sleep in general, without specific reference to infants, whose sleep patterns are decidedly different. Other studies refer to sleep difficulties in toddlers and children, but not in infants. Some of the research lacks clear, objective criteria for defining such terms such as sleep “problems” or “difficulties.” I have not seen any study that concludes that sleep training is actually beneficial to babies. I did read studies maintaining that such training is not detrimental to an infant, in either the short or long run. The question is whether “not detrimental” is a sufficient conclusion when it comes to an attempt to change our children’s behavior.

Many parents relate that sleep training absolutely saved them. Do you think that behavioral intervention in a baby’s sleep is never good?

Parents shouldn't deceive themselves into thinking that sleep training is done for the good of the infant or the toddler. From the child’s perspective, it's is a cruel and unusual punishment.


“All I can do is accept the fact that in certain circumstances there are parents who will insist on that kind of training in order to optimize their rest. But it’s important that they not deceive themselves into thinking that it’s being done for the good of the infant or the toddler. No matter how we look at it, from the child’s perspective, sleep training is a cruel and unusual punishment even at later ages, which has to do with processes such as weaning and basing nutrition on solid foods, and not with ‘regularizing’ the child’s sleep.”

Your study deals for the most part with an age in which the human infant is completely helpless. Until what age do you advocate co-sleeping with children?

“There is no biological boundary that states that a child should not or does not want to co-sleep with its parents in order to feel safe and protected, as long as it’s appropriate for everyone. In the case of toddlers and children, it’s no longer a purely biological thing, it’s social. The social circumstances, which are a by-product of Western society, are what transform co-sleeping at this stage in the child’s life into a less successful experience for the adults, and that is perfectly fine.”

Continued tradition

“We are not kind enough to our infants,” McKenna sighs toward the end of our conversation, “we are not polite enough to them.” In large measure, he has devoted more than 40 years of research to helping introduce something of that goodness into our behavior with our offspring – a process that perhaps will also make us polite and beneficent toward ourselves. If we only internalize that we are not a potential harm to our children, that there is no need to invest in ‘correcting’ them – that it’s enough to maintain close contact.”

In the end, he can look back with satisfaction. The conclusions of his research are trickling down ever more into the heart of the medical establishment, he is a lecturer much in demand and is courted by scientific journals, as well as holding a professorship at Santa Clara University, in California. In keeping with the principle of practicing what he preaches, McKenna is also applying his ideas about the importance of physical closeness to his toddler grandson who lives nearby, and enjoys seeing that his son is also continuing the tradition of close contact with his son.

“That,” he sums up, “is the greatest satisfaction.”

Einat Talmon is a lactation consultant (IBCLC).

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