A key feature of the care of infants and young children among hunters and gatherers is proximity between mother and infant. Close physical contact is the rule, and the infant's dependent needs and even their mere demands are routinely indulged. The !Kung San have been more carefully studied with regard to this pattern than any other hunting and gathering group. Young infants are in physical contact – contact, not just proximity – with someone (usually the mother) for at least 90 percent of the time during the first few months of life, and this declines only gradually to around 25 percent in the middle of the second year. This is direct skin-to-skin contact with the physical warmth and stimulation that implies. Infants and young children sleep on a mat beside the mother (the equivalent of sleeping in the same bed), with the father usually also nearby.

Crying in infancy and early childhood is not considered a symptom of "spoiling" or any other negative psychological condition, but simply a condition of infancy. In the words of one !Kung San woman, confronted with Dr. Spock's recommendation that a baby who frequently cries to be picked up must be put through a process of "unspoiling," "Doesn't he realize she's only a baby and that's why she cries? She has no sense yet, so you have to pick her up. Later, when she's older, she'll have sense, and she won't cry any more."

This aptly expresses the !Kung San theory of child development: You can't rush it; they go through stages, and you have to respond promptly to their dependent needs because it would be wrong not to – a form of child abuse or neglect. The common American practice of letting the baby "cry it out" is quite abhorrent to them. Measured objectively, they respond to infant crying within an average of six seconds. They pride themselves on anticipating an infant's needs before crying begins. For example, they are usually successful in anticipating when the baby is about to urinate or defecate, and they take the baby out of its carrying sling for that purpose. Even aggressive acts by the young child are indulged – hitting the mother with a stick, for example – on the grounds that this is just another phase. Of neighboring herding people who are less indulgent and more strict, they say: "They don't like children."

So much for the !Kung San of the Kalahari. But to what extent does this apply to other hunting and gathering groups, or for that matter to other types of preindustrial societies?

The pattern of physical closeness, like the pattern of intensive prolonged breastfeeding, appears to be very general. More or less constant carrying of the infant in a sling or pouch at the mother's side or back is characteristic of hunters and gatherers in widely separated geographic regions, including the Pygmies of Zaire, the Siriono of the Amazon Basin, the Paliyans of the Indian peninsula, the Yahgan of Tierra del Fuego, the sub-Arctic and Arctic Eskimo, and the Australian Aborigines. Among the Ache of Paraguay the pattern of mother-infant contact is even more intense than that of the !Kung. It has been established by cross-cultural analysis that nearly all preindustrial people living in warm climates (whether hunters and gatherers or not) tend to have carrying devices that keep them in direct physical contact with their infants. Since the great majority of human evolution took place in warm climates, this finding increases the likelihood that our ancestors had close mother-infant physical contact. But even cold-climate hunters and gatherers such as the Eskimo and the Yahgan have close contact, suggesting the pattern is characteristic of hunters and gatherers regardless of temperature. Among the Eskimo, for example, the woman's parka was cut larger than the man's so that an infant could fit inside it, and infants rode naked except for their caps most of the time, in a hide sling on the mother's naked back.

What about sleeping proximity? This too has been carefully studied in cross-cultural surveys. Close mother-infant proximity is the rule, not the exception. In a study of ninety preindustrial societies for which information was available in regard to sleeping distance, 46 percent had mother and infant sleeping in the same bed, as with the !Kung San; 33 percent had mother and infant sleeping in the same room, but did not specify whether they were in the same or in separate beds; and 21 percent had mother and infant sleeping in the same room but in separate beds. There was no society in which mother and infant slept in separate rooms, even in societies with multiroom dwellings; this appears to be an innovation of recent European society.

This may in part be related to space availability. But at least one study in the United States found that some working-class families with many rooms still keep infants in the same room with their mothers, while some professional-class families with tiny apartments often keep infants in a crib in the kitchen – just to insure that they have a separate room. Even traditional cultures with one-room houses do not have to keep their infants on the same bed or mat, as half or more of them do. And in any case, whatever the reason for the close sleeping arrangement, the infant's experience is the same. Thus the !Kung San pattern of mother-infant proximity – often even direct physical contact – is a widespread characteristic of hunting and gathering and to a lesser extent other traditional societies, and was consequently almost certainly the pattern followed by our Paleolithic ancestors.

It is not difficult to see why, considering our evolutionary background. Intensive maternal care of the young was not invented by mammals, but it was one of the evolutionary hallmarks of these warm-blooded creatures. By the time our closest relatives, the higher primates, appeared, this pattern had been refined to an exquisite degree. Every known species of monkey or ape without exception has round-the-clock mother-infant physical contact or close proximity, with the time in contact declining only gradually as the infant becomes more independent. This is most likely attributable to the fact that an infant alone in the wild is immediately vulnerable to predation. Scientists studying monkeys in their natural habitats have observed infants taken by hawks and snakes, and this would have been a constant evolutionary force promoting the success of mothers (and, in some species, fathers) and infants who maintained close contact. Against this background, the widespread characteristic parent-infant closeness in fundamental human adaptation seems easy to understand.

Although the indulgence of dependency (other than breastfeeding) is more difficult to investigate, that too seems to be a pattern widespread among hunters and gatherers. Using a large compendium of cross-cultural data known as Textor's Cross-Cultural Summary, it is possible show how different types of societies view this issue, according to the descriptions of the ethnographers who have studied them. The results? Simpler societies have more indulgent infant- and child-care practices than do more complex ones. To take the comparison between foraging societies and other nonindustrial societies as an example, the amount of pain inflicted on the infant (through customary scarification, circumcision, and other practices) was found to be less among foragers; the amount of overall indulgence  –  responsiveness to infant demands  –  found to be greater; the severity of toilet training less; and the child's anxiety over responsible, obedient, and self-reliant behavior less in each case among foragers.

A more intensive study comparing 10 tropical hunting and gathering societies with 176 other nonindustrial societies was carried out by two pediatricians also interested in what hunting and gathering baby and child care has to tell us about our own practices. Their data confirmed that very close mother-infant contact, late weaning, and indulgent responsiveness to infant crying were more characteristic of hunting and gathering societies than they were of other nonindustrial ones.

The same authors went on to compare the 176 nonindustrial nonforaging societies with ourselves. Despite the fact that these societies were less indulgent of infant dependency and had less close mother-infant contact than did the 10 tropical hunting and gathering societies, they still had more of both than we do. Whether measured by body contact, sleeping distance, response to crying, or weaning age, mother-infant contact and maternal indulgence of infants appeared to be less in the United States than in the broad cross-cultural range. This finding supports the much older finding of anthropologist John Whiting, who in a 1953 study with Irvin Child, reported that patterns of infant and child care in the middle class of Chicago during the 1940s were substantially less indulgent than comparable patterns in a large representative sample of nonindustrial societies (including some hunters and gatherers). Except, that is, in the area of aggressiveness, where the Chicagoans were more permissive. In other words, in the areas of feeding, toilet training, sex and modesty training, and independence training, children were placed under more pressure to conform to pre-set standards in Chicago than in the wide range of nonindustrial societies. Only in the area of children's aggressiveness were the Chicagoans less strict.

Two conclusions seem reasonable. First, that hunters and gatherers are more indulgent of infant needs and demands than are other types of nonindustrial societies, and second, that (although those other societies exhibit a great deal of variation) they tend to be less strict with infants and children and more responsive to them than we are. This finding repeats previous observations regarding the intensity and length of breastfeeding and the amount of mother-infant physical contact and proximity. Overall, then, we can infer that during most of the Paleolithic, our early human ancestors extended the patterns of our higher primate ancestors in mother-child relations – patterns that almost certainly go back not only millions but tens of millions of years.