Infants and young children in our culture regularly protest going to bed. They make all sorts of excuses. They say they are not tired, when in fact they obviously are tired. They say they are hungry, or thirsty, or need to hear a story (and then one more story)–anything to stall. They talk about being afraid of the dark, or afraid of monsters in the closet or under the bad. Little babies without language, who can't yet describe their fears or try to negotiate, just scream.
Why all this protest?
Many years ago, the famous behavioral psychologist John B. Watson argued, essentially, that such behavior is pathological and derives from parents' overindulgence and spoiling of children. Remnants of that view still persist in books on baby care, where the typical advice is that parents must be firm about bedtime and not give in. This, the experts say, is a battle of wills, and you, as parent, must win it to avoid spoiling your child.
But clearly something is missing in this explanation from the experts. Why do infants and young children choose to challenge their parents' will on this particular issue? They don't protest against toys, or sunlight, or hugs (well, usually not). Why do they protest going to bed, when sleep is clearly good for them and they need it?
The answer begins to emerge as soon as we leave the Western world and look at children elsewhere. Bedtime protest is unique to Western and Westernized cultures. In all other cultures, infants and young children sleep in the same room and usually in the same bed with one or more adult caregivers, and bedtime protest is non-existent..
What infants and young children protest, apparently, is not going to bed per se, but going to bed alone, in the dark, at night. When people in non-Western cultures hear about the Western practice of putting young children to bed in separate rooms from themselves, often without even an older sibling to sleep with, they are shocked.
"The poor little kids!" they say. "How could their parents be so cruel?" Those who are most shocked are people in hunter-gatherer societies, for they know very well why young children protest against being left alone in the dark.
What hunter-gatherers already knew
Until a mere 10,000 years ago we were all hunter-gatherers. We all lived in a world where any young child, alone, in the dark, would have been a tasty snack for nighttime predators. The monsters under the bed or in the closet were real ones, prowling in the jungle or savannah, sniffing around, not far from the band's encampment. A grass hut was not protection, but the close proximity of an adult, preferably many adults, was protection.
In the history of our species, infants and young children who grew frightened and cried out to elicit adult attention when left alone at night were more likely to survive to pass on their genes to future generations than were children who placidly accepted their fate. In a hunter-gatherer culture, only a crazy person or an extremely negligent person would leave a small child alone at night, and at the slightest protest from the child, some adult would come to the rescue.
When your child screams at being put to bed alone at night, your child is not trying to test your will! Your child is screaming, truly, for dear life. Your child is screaming because we are all genetically hunter-gatherers, and your child's genes contain the information that to lie alone in the dark is suicide.
The evolutionary mismatch
This is an example of the concept of evolutionary mismatch. We have here a mismatch between the environment of our evolutionary ancestors, in which our genetic being was shaped, and the environment in which we live today.
In the environment of our evolutionary ancestors, a child alone at night was in serious danger of being eaten. In the environment of our evolutionary ancestors, no sane parent–or grandparent, or uncle, or aunt, or other adult band member–would ever let a small child sleep alone. If a child were inadvertently left too far from an adult in the dark at night, the child's cry would be immediately heeded.
Today, a child alone at night is not in serious danger of being eaten. Without the realistic dangers, the child's fear seems irrational, so people tend to assume that it is irrational and that the child must learn to overcome it. Or, if they read the "experts," they learn that the child is just testing their will and acting "spoiled." And so, people battle their child rather than listen to both the child and their own gut instincts that tell them that any crying baby needs to be picked up, held close, and cared for, not left alone to "get over it."
What we can do
What do we do about evolutionary mismatch? In this case, two alternatives appear. We can do what the "experts" advise and engage in a prolonged battle of wills, or we can do what our genes advise and figure out some not too inconvenient way to let our children sleep close to us.
When my own son was small, long ago when I was a graduate student, the choice was easy. We lived in a one-room apartment, so there was no way to put him to bed separate from us. In some ways, life is easier when you are poor than when you can afford an apartment or house with more than one room.
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 Watson, J. B. (1928). Psychological care of infant and child. New York: Norton.
 Barry, H., & Paxson, L. (1971). Infancy and early childhood: Cross-cultural codes, 2. Ethnology, 10, 466-508. // Morelli, G. A. et al. (1992), Cultural variation in infants' sleeping arrangements. Questions of independence. Developmental Psychology, 28, 604-613.
 Konner (2002). The Tangled Wing: Biological constraints on the human spirit (2nd ed.). New York: Holt.