Since the beginning of our species, human families have shared sleeping spaces out of necessity, for comfort, safety, and warmth. The infant child of a caveman left apart from his parents for the night may very well have not lived till morning, perishing in the cold, or getting carried away by some predator. The baby’s cry when left alone served as an adaptive reminder to Mom and Dad, “Don’t forget about me! I’m completely helpless and defenseless without you!” And the strong emotional response that cry evoked from his mother also served a purpose. She felt a deep need to soothe him and protect him from danger.
In the United States and most of the civilized world today, a baby left in a crib at night is in no danger. However, since we humans have not evolved since ancient times, our babies are born programmed with the same instincts and fears that allowed our species to survive. There is nothing we can say during the daytime to explain to an infant that he will be safe at night. His only comfort is the constant closeness of a loving caregiver.
Throughout most of history and even today, in most societies, babies are considered to be natural extensions of their mothers. Their need to be with Mother (or other loving caregiver) day and night is not questioned. Solitary infant sleep and sleep training are unique to our culture, and only about two hundred years old.
Parents sharing sleep spaces with infants and children first fell out of favor in Western culture during the 1800s, when a “sterile” approach to raising children began to be advocated by doctors and so-called experts. Coincidence or not, this occurred at the same time when germ theories were first being developed, and it was thought that eliminating human contact altogether was the ideal state for preventing disease. During this time, mothers were advised that to keep their children from becoming “spoiled,” they should refrain from too much cuddling and kissing. Babies were expected to be “trained” to sleep on their own.
And the trend continued. Formula, first invented for infants who could not be breastfed, soon became standard for all babies. Bottles replaced Mother’s breasts, carriages replaced Mother’s arms, and cribs replaced Mother’s warm bed. With the arrival of these new inventions came a host of previously unheard-of complaints. What could be done with the “clingy” baby who wanted to be held all the time? The baby that could not learn to soothe himself to sleep alone in his crib? The adaptations that previously allowed the infant to survive now earned him the label of a “difficult” child.