Let's try an experiment. All new moms will offer their breasts to their newborn whenever the child fusses (as done traditionally among humans and as illustrated for "Africa" here) for at least 4 months. This is what I think will happen (based on longstanding traditions and on empirical research):
First, there will be next to no crying, unlike the typical expectation for lots of crying in the first three months of life. Mothers respond to the gestures of the child or initial grunts before crying ever ensues.
Second, the mother will learn to be sensitive to her child's cues for support, getting the relationship off to a good start.
Third, the baby will be happy and healthy from never getting worked up and from having the magnificent brain and body-building elixir, breastmilk, which washes the brain with its hormones and keeping the digestive system coated with protection from infectious disease.
If the mother continues to be responsive in this way for the first year, there will be longterm benefits for the family and society in having a healthy child with an agreeable personality and a well-functioning mother-child pair.
Now what does it take to make this possible? The mother needs paid leave from work. The mother needs support from her family and friends. Of course, the mother, family, friends and social policy makers all need to understand the importance of breastfeeding and meeting the child's needs quickly. Actually, everyone in the whole society will need to know these things.
What do you know about breastfeeding? If you want, take this survey and find out how much you know, helping us out with our research on misconceptions about breastfeeding.
But if on the other hand you expect babies to cry a lot, how do you make sure that happens? Respond inconsistently to the baby's needs.
What does inconsistent response do?
In short, inconsistent response undermines the foundations for social relationships, which means it undermines moral behavior later.
That's right, moral development starts from birth. How mom and other caregivers respond to baby puts the baby on a trajectory for sensitive or insensitive morality.
Sometimes babies do cry at a particular time of day, no matter what the parent does (see comments below). It is not clear why this happens because it would not have been adaptive among our ancestors, whose predators could find them if a baby was crying, But it happens in modern societies. Perhaps a thorough examination of our food supply is warranted. Other modern factors may also play a role, like lighting at night, parents not going to sleep when it gets dark next to the baby, or some combination of factors for a particular child.
For a summary of anthropological evidence see Melvin Konner's 2010 book, The Evolution of Childhood; Barry Hewlett and Michael Lamb's 2005 book, Hunter-Gatherer Childhoods.
I am working on two books summarizing the research supporting the conclusions drawn here (an edited volume with chapters by researchers with Oxford University Press and the other book linking all this to moral development with WW Norton). Meanwhile for a summary of the effects of early life experience on child development see Allan Schore's books and work by Bruce Perry, and Dan Siegel.