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Infant care: Cache or carry
B E H A V I O R A L
P E D I A T R I C S
Richard W. Olmsted, E d i t o r
Infant care: Cache or carry To test the hypothesis that a characteristic infant-care pattern existed during most o f human history, contemporary hunter-gatherers in a representative sample o f world cultures were examined. Numerically coded measures of infant care revealed a uniform pattern. Mothers are the principal caregivers,, providing extensive body contact day and night and prolonged breast-feeding. When not carried, the baby o f hunter-gatherers has complete freedom of movement. Care ts consistently affectionate, with immediate nurturant response to crying. Nonetheless, in most groups, children achieve early independence and by 2 to 4 years spend more than half the time away from the mother. In the United States this pattern of carrying that endured f o r one to three million years has been replaced by one resemb#ng nesting or caching. Infants spend little time in body contact with earegivers and their movements are restricted by playpens, high chairs, or cribs. O f the minority who are breast-fed, half are weaned within a few weeks. Separate sleeping arrangements and delayed response to crying are regularly recommended. These remarkable transformations may profoundly alter infant development and maternal involvement.
Betsy Lozoff, M.D.,* and Gary Brittenham, M.D.,** C l e v e l a n d , O h i o
INFANT CARE in the United States and other industrialized countries no longer resembles that provided during most of human history. Breast-feeding has been supplanted or strikingly altered by the availability of breast milk substitutes, and infants have little contact with caregivers, sleep separately, and spend much of their day in playpens, high chairs, or cribs. The anthropologic evidence presented in this paper indicates that a very different pattern of infant care existed during most of the historyof the human species. One alteration, the abandonment of breast-feeding, has aroused widespread concern because of the effects on maternal fertility and infant health and survival/ The impact of changes in other features of infant care has not been examined, but the consequences for infant development and maternal involvement may be as profound. The presence of a characteristic pattern of infant care From the Departments o f Pediatrics and Medicine, Divisions o f Geographic Medicine and Hematology, Case Western Reserve University School of Medicine and Rainbow Babies and Childrens Hospital. Supported in part by a grant from the Rockefeller Foundation. *Reprint address: Division of Geographic Medicine, Deparfmem of Medicine, University Hospital~, Cleveland, OH 44106 **Teaching and Research Scholar of the American College of Phystcian~
478
The Journal o f P E D I A T R I C S Vol. 95, No. 3, pp. 478-483
during the course of human evolution is suggested by studies in comparative physiology.2.3 Among terrestrial mammals, species may be divided into those with extensive contact between mother and infant (the young are carried by, hibernate with. or follow the mother) and those with intermittent contact (the young are cached in secluded places or left in nests or burrows while the mother is absent for extended periods). These differences are reflected in breast milk composition and the interval between feedings. In species with intermittent contact. infants are adapted for separations by receiving their iotal nutritional requirements_ in spaced feedings during the mother's visits: milk ~" high in protein and fat. and feedings take place every two to 15 hours. A similar pattern of spaced feeding is conceivable in species with extensive maternal contact, but is not observed: feedings are frequent (every one to two hours) or essentially continuous, and milk is low in protein and fat. Even if the "continuous" feeding mammals are compared with those which nest their young and feed as frequently as every two to four hours, significant differences in milk composition remain.' Human milk is low in fal and extremely low in protein, suggesting that the human infant is adapted to frequent feeding and extensive maternal contact. Since human babies cannot follow their mothers at birth and do not hibernate with them. comparative physiology identifies the human pattern of infant care as that of carrying.
0022-3476/79/090478 +06500.60/0 9 1979 The C. V. Mosby Co.
Volume 95 Number 3
Infant care." Cache or carJy
479
Table. Frequency of selected infant care practices in hunter-gatherer and other nonindustrialized societies: Comparison with the United States
Huntergatherers n = 10 (%)
Other nonindustrial societies n = 176 (%)
9 1. Infant carried or held more than 50% of the time until age of trawling (3a:4-5) 2. Mother is principal caregiver in infancy (13a: 1-3) 3. Mother sleeps with the infant in same bed or room (1:5-9) 4. Generally affectionate care in infancy and in early childhood (16a & b:4-5) 5. Immediate, nurturant response to crying (5a:4-5)
100
56
Body contact 25% of the time
100 100
9O 76
Mother is principal caregiver'~ Separate sleeping recommended
100
505
No quantitative data
100
74
6. Complete freedom of movement after age of crawling (2b: 1)w 7. Infant carried with sling or no carrying device (4a: 1-3) 8. Breastfeeding for 24 months or more (ll:mean >__24 months) 9. Peer group is principal companion in early childhood (15b: 1-3) 10. Early gradual independence and autonomy (10a:3-4) 11. Child spends 50% of the time away from mother in early childhood (13b:3-5), 12. Father frequently and closely involved in early childhood (14b:4-5)1[
100
39
43% crying episodes ignored; delayed response advised Movement generally restricted
90
76
No quantitative data
86
83
6% breast-feeding at 6 mo
86
35
No quantitative data
75
70
No quantitative data
75
75
No quantitative data
75
53
No quantitative data
Infant care practices*
United States
;~Thedescriptive phrases 1 to 12 are'derived from the Barry and Paxsoncodes?~In parentheses are the column number and the ratings for which the practice was judged present. tCare often provided by unrelated individualsor institutionslike day ca~'ecenters. ~72% in infancy (16a). w age of crawling, 80% among hunter-gatherersand 25% in other non-industrialsocieties (2a:1). []In infancy, 63% among hunter-gatherersand 33% in other non-industrial societies (14a:4-5). Which h u m a n societies should be examined for a "characteristic" pattern of infant care? Industrialized societies are not appropriat e , for these have been present for a mere instant Of the species' existence: If all h u m a n history were represented by an hour, the last o n e / one-hundredth of a second would represent the 200 years of industrialization. Settled agriculture appeared only 10,000 Years (one-third of a second) ago. The mode of subsistence for over 99% of the species' two to three million-year history was hunting and gathering in the tropics. ~ 6 Therefore, data from the few surviving tropical foraging groups provide the best available indication of the care to which the h u m a n infant was adapted. 7, ~ Societies depending 'on h u n t i n g and gathering for subsistence are composed of small mobile groups, usually of 30 tO 100 people. ~ Population size is typically greatly belOw that which could be supported in a given area, .and is Stable, with babies born three to four years apart. TM The hunting of m a m m a l s provides 20% or more of the diet. 1.....
Food gathering, generally by women, supplies 40 to 60% 0f the total diet in most h u n t i n g and gathering societies. 1~ Since vegetable and anima! supplies can be exhausted if a band stays in one place t o o long, mobility is essential to this way of life. A n extreme example is provided by the !Kung San of the Kalahari Desert in Africa, who walk 3,000 miles per year? ~ This existence, even in a marginal environment, is not as arduous as might be thought. Quantitative studies have suggested that a nutritionally adequate diet may be obtained with a modest effort of two to five hours per day, leaving a substantial reserve of both h u m a n energy and environmental resource. 16-1~ Our observations'among ethnic groups in India who live primarily by hunting and gathering led us to postulate that a specific Pattern of infant care preva!led during most of h u m a n history, and would still predictably be found among present hunters and gatherers. This hypothesis Was tested bY analysis of encoded data on infant care in a representative sample of nonindustrial societies.
Lozoff and Brittenham
480
m
ioo
The Journal of Pediatrics September 1979
! I'(ung
F-no ffl
n,w m o
I
I
I
I0
20 AGE (Weeks)
30
Figure. Infant bodily contact among the !Kung San and in the United States. 9 9 = Percentage of spot observations that infant is in physical contact with caregivers among the !Kung San, redrawn from Konner8 and modified to show average of data for male and female infants. X---X = Percentage of time during continuous observations that infant is in bodily contact with the mother in the United States, from the data of Ainsworth et al.2~ During the United States observations the mother was usually the only individual having body contact with the. infant.
MATERIALS
AND METHODS
To compare infant-care patterns in the United States with those in hunting and gathering and other nonindustrial societies, anthropologic, psychologic, and pediatric sources were studied. Murdock and White's sample 2~ of 186 geographically, linguistically, and historically representative nonindustrial societies was examined. Tropical hunter-gatherers were defined as societies living between latitudes of 22030 ' N and 22030 ' S, depending primarily o n hunting and gathering for subsistence (Murdock and Morrow's Subsistence Economy,! 2 Code of S or D in Columns 5 and 6)i with less than 10% dependence on agriculture, animal husbandry, and fish!ng !Code 0, N, or U in Columns 3 and 4 a n d O or U in Column 5). Ten societies met these criteria: the IKung Bushmen, Hadza, Mbuti, Semang, Vedda, Tiwi, Siriono, Botocudo, Shavante, and Chenchu. The numerically coded measures of infant care presented by Barry and Paxson ~ were studied. These codes are based On the typical cultural practices for male middle-born children, and most are defined according to a quantitative scale from 1 to 5. Barry and Paxson ratings based on highly unreliable information or considered highly inferential were excluded. The features of infant care we scored are indicated by the descriptive phrases used in the Barry and Paxson codes (Table); the column number i n the Barry and Paxson codes is listed in parentheses along with the ratings for which the feature was judged to be present. The proportion of the huntinggathering societies in which the item of infant care was
found was calculated. The remaining 176 societies were similarly scored for the items shown. Where an alternate society was specified, the one with the most complete infant codes was chosen. Since breast-feeding schedules were not coded, descriptive accounts 8, 23-2~were examined to assess feeding frequencies. Finally, psychologic and pediatric sources 2~-37were used to determine the presence of the same features in the patterns of infant care in the United States. RESULTS
AND INTERPRETATIONS
A consistent pattern of infant care is found among the hunter-gatherers (Table). The aspects of care listed as numbers 1 to 9 in the Table are found in all the foraging societies, or in all with a single exception. In hunting and gathering societies infants are carried or held more than half the day until the age of Crawling. Infants are carried in close body Contact, either with no carrying device or with a sling or flexible Pouch, allowing the infant to mold to the mother's body. While carrying babies, the women gather food, a typically female activity which supplies about half the diet in most foraging societies. Infant carrying is thus compatible with women's work. The mother is always the principal caregiver, contact is extensive, day and night, and breast-feeding is prolonged (-->24 months). CarefUl observations among the !Kung document essentially continuous nursing, 8 and at least frequent breast-feeding on demand is reported for other societies.~3-2~Infant carrying does not imply restriction. When not held, the hunter-gatherer baby has complete freedom of movement except in emergencies, both in early infancy and after crawling. Care is uniformly affectionate, with a n immediate nurturant response to crying. The close responsive relationships a n d extensive body contact d 0 not seem to create overly dependent children. Autonomy 'and independence are generally early and gradual, so that by two to four years of age children spend more than half the day away from the ~ o t h e r in the company of peers. Usually the father is frequently and closely involve d with the child. To determine whether elements of the infant-care pattern among hunter-gatherers are widely practiced, the remaining 176 Societies were analyzed. These are nonindustrial societies with subsistence activities that have existed for/less than 1% o f human time: agricu!ture, herding, or; fishing. The prevalence of the selected features of infant care in these other societies is shown in the Table. In most the mother is still the principal caregiver, sleeps in the same bed or room, and breastfeeds for more than two years. Infants are likely to receive an immediate nurturant response to crying, and achieve
Volume 95 Number 3
early independence. In comparison with the nomadic hunter-gatherers, among whom carrying is universal, in only 56% of the other societies are young infants carried for more than half of the time. Extensive body contact and freedom of bodily movement are no longer provided in many of these societies. In the United States and other industrialized nations and among the urban poor of many developing countries, infants spend little time in body contact with caregivers. The Figure compares infant carrying in a United States' study with the !Kung of the Kalahari Desert. The !Kung infant is held or carried 80 to 90% of the time during the early months and 60% of the time at nine months? The United States' baby is held one-third of the time during the first three months and only 16% by nine months. 2~ Infant care has undergone further striking changes, shown in the Table. Mothers are still the principal caregivers, although institutions like day-care centers play an increasing role. Separate sleeping arrangements are the usual pediatric recommendation. 27' 2~ Of the minority of infants who a r e breasi-fed, half are weaned within a few weeks 26-3~ and only 6% continue as long as six months. 3~ Even when breast-feeding occurs, it is usually managed like bottle feeding, spaced every two to four hours. In the many hours of the day that infants are not held, their movements are often restricted by playpens, high chairs, and cribs. A restrained approach to infant demands and a delayed response to crying are generally advised. 2" In the United States' study cited above, a mean of 43% of infant crying episodes (not just momentary fussing) were ignored during the first year of life? 7 Comparable data about independence are not available. DISCUSSION Infant carrying and prolonged breast-feeding, observed among contemporary foraging societies, may have been an integral part of the regulation of population size during our species' two to three million-year history?* The birth of a c h i l d dramatically altered the mother's energy balance. She continued to participate in the group's periodic migrations and the women's daily foraging excursions, but for a two to three-year period also carried her child. Lactation required an additional expenditure of energy. Unless these new caloric needs were met by increased food intake, the required energy was drawn from maternal fat reserves. If it is true that the proportion of fat in a woman's body helps regulate the entire cycle of fertility and fecundability,~9-4~then the infant-care pattern was essential to maintain the three to four-year birth interval of hunter-gatherers, especially where infanticide and sexual practices played minor roles. By reducing the
I n f a n t care: C a c h e or carry
48 1
mother's proportion of body fat below that necessary for ovulation, the energy expended in breast-feeding and carrying a baby resulted in an extended period of postpartum infertility. Under conditions of food scarcity, the reaccumulation of fat reserves would have been even further delayed, the birth interval lengthened, and a balance maintained between environmental resources and population size. However, since scarcity has been considered rare among hunter-gatherers, 1~-19 the low fat proportions were probably not due to lack of food but to the vigorous active existence and high level of physical fitness. After the birth of a child, women may not have changed lifetime habits to collect and consume more food, and the proportion of fat would thus drop below that required for ovulation. A birth interval of three to four y e a r s allowed each infant to complete the period of maximal need for the mother 43.44 without competition from other young siblings. During this time the infant had extensive body contact with the mother, both day and night. The care provided was highly responsive and consistently affectionate, nurturant, and unrestrictive. By three to four years the child had achieved a degree of independence and autonomy sufficient to allow the mother to carry and care for a new infant. Comparison of the scoring of the remaining 176 representative nonindustrial societies with that of the hunters and gatherers shows many similarities. Carrying, extensive body contact, and unrestricted bodily movement are no longer common, but in most the mother is still the principal caregiver, sleeps in the same bed or room as the infant, and breast-feeds for two years or more. The pattern of carrying that endured for at least two million years has been replaced in the United States by one resembling nesting or caching. Infants spend little time in body contact with caregivers. In spite of the availability of medical means of contraception, the birth interval is often one to two years 46 and several infants may compete for maternal concern. Care for infants generally involves intermittent maternal attention, artificial feeding or spaced breast-feeding, restriction of bodily movement, and restraint in response to infant needs. The fact that a pattern of behavior was adaptive for most of the species' history does not necessarily imply that it continues to be so, nor that it is desirable. Data on parenting disturbances, family disruption, and mental illness among hunter-gatherers are scant; these problems may have been as common in our preagricultural past as they are in our industrial present. Nonetheless, the remarkable transformations in the pattern of infant care which have occurred in the last few hundred years may
482
L o z o f f and Brittenham
have h a d a p r o f o u n d i m p a c t o n n o r m a l infant developm e n t and n o r m a l m a t e r n a l i n v o l v e m e n t . Research on the effects of i n f a n t care is difficult and investigations of the issues raised here are especially so. Studies c a n n o t be restricted to industrialized societies; a b a b y receiving high levels o f m a t e r n a l b o d y c o n t a c t by U n i t e d States' standards would b e j u d g e d d e p r i v e d a m o n g hunter-gatherers. In spite of the difficulties, such research seems crucial for the choice of future p a t t e r n s o f i n f a n t care: cache or carry.
REFERENCES
1. Knodel J: Breastfeeding and population growth, Science 198:1111, 1977. 2. Blurton Jones N: Comparative aspects ~of mother-child contact, in Blurton Jones N, editor; Ethological studies of child behaviour, London, .1972, Cambridge University Press, p p 305-328. 3. Ben Shaul D: The composition of the milk of wild animals, Int Zoo Year Book 4:333, 1962. 4. Lozoff B, Brittenham GM, Trause MA, KenneU JH, and Klaus MH: The mother-newborn relationship: Limits of adaptability, J PEDIATR 91 : 1, 1977. 5. Lee RB, and DeVore I: Man the hunter, Chicago, 1972, Aldine Publishing Company. 6. Lee RB, and DeVote I: Kalahari hunter-gatherers, Studies of the !Kung San and their neighbors, Cambridge, 1976, Harvard University Press. 7. Konner MJ: Aspects of the developmental ethology of a foraging people, in Blurton Jones N, editor: Ethological studies of child behavior, London, 1972, Cambridge University Press, pp 285-304. 8. Konner M J: Maternal care, infant behavior and development among the !Kung San, Kalahari hunter-gatherers, Lee RB, and DeVore I, editors: Studies of the !Kung San and their neighbors, Cambridge, 1976, Harvard University Press. 9. Hassan FA: Determination of the size, density and growth rate of hunting-gathering populations, in Polgar S, editor: Population, ecology and social evolution, The Hague, 1975, Moulton Publishers, pp 27-52. 10. Dumond DE: The limitation of human population: a natural history, Science 187:713, 1975. 11. Angel LJ: Paleoecology, paleodemography and health, Population, in Polgar S editor: Ecology, and social evolution, The Hague, 1975, Moulton Publishers, pp 167-190. 12. Callen EO: Dietary patterns in Mexico between 6500 BC and 1580 AD, in Smith CE, editor: Man and his foods, University, Ala., 1973, University of Alabama Press, pp 29-49. 13. Isaac G: The diet of early man: aspects of archaeological evidence from lower and middle pleistocene sites in Africa, World Areheol 2:278, 1971. 14. Lee RB: What hunters do for a living, or, How to make out on scarce resources, in Lee RB, and DeVore I, editors M a n the hunter, Chicago, 1968, Aldine Publishing Company, pp 30-48. 15. Martin MK, and Voorhees B: Female of the species, New York, 1975, Columbia University Press.
The Journal o f Pediatrics September 1979
16. Lee RB: Mongongo: the ethnography of a major wild food resource, Ecol Food Nutr 2:307, 1973. 17. McCarthy D, and McArthur M: The food quest and the time factor in aboriginal economic life, in Mountford CP, editor: Records of the Australian-American expedition to Arnhem land, Vol 2, Anthropology and nutrition, Melbourne, 1960, University Press, p 181. 18. Wehmeyer AS, Lee RB, and Whiting M: The nutrient composition and dietary importance of some vegetable food eaten by the !Kung Bushmen, S Afr Med J 43:1529, 1969. 19. Sahlins M: Stone age economics, Chicago, 1972, Aldine Publishing Company. 20. Murdock GP, and White DR: Standard cross-cultural sample, Ethnology 8:329, 1969. 21. Murdock GP, and Morrow DO: Subsistence economy and supportive practices: cross-cultural codes 1, Ethnology 9:302, 1970. 22. Barry H, and Paxson L: Infancy and early childhood: cross-cultural codes 2, Ethnology 7:466, 1968. 23. Holmberg AR: Nomads of the long bow. The Siriono of Eastern Bolivia, New York, 1969, Natural History Press. 24. Maybury-Lewis D: Akwe=Shavante society, New York, 1974, Oxford University Press. 25. Jelliffe DB, Woodburn J, Bennett F, and Jelliffe EFP: The children of the Hadza hunters, J PEDIATR 60:907, 1962. 26. Blehar MC, Ainsworth MD, and Bell SM: Developmental changes in the behavior of infants and their mothers relevant to close bodily contact (monograph in preparation). 27. Vaughn VC, and McKay RJ, editors" Nelson textbook of pediatrics, Philadelphia, 1975, WB Saunders Company, p 217. 28. Spock B: Baby and child care, New York, 1976, Pocket Books. 29. Sloper K, McKean L, and Baum JD: Factors influencing breast feeding, Arch Dis Child 50:165, 1975. 30. Davies DP, and Thomas C: Why do women stop breast feeding? Lancet 1:420, 1976. 31. Bax CO, and Hart H: Encouraging breast-feeding, Lancet 2:1214, 1976. 32. Coles EC, Cotter S, and Valman HB: Encouraging breastfeeding, Lancet 2:978, 1975. 33. Report of new mothers survey, Data on file at Ross Laboratories, 1975. 34. Harfouche JK: The importance of breast-feeding, J Trop Pediatr 16:133, 1970. 35. Sjolin S, Hofvander Y, and Hillervik C: Factors related to early termination of breast feeding, Acta Paediatr Scand 66:505, 1977. 36. Fomon SJ: What are infants fed in the United States? Pediatrics 56:350, 1975. 37. Bell SM, and Ainsworth MDS: Infant crying and maternal responsiveness, Child Dev 43:1171, 1972. 38. Howell N: Toward a uniformitarian theory of human paleodemography, J Human Evol 5:1, 1976. 39. Frisch RE: Demographic implications of the biological determinants of female fecundity, Social Biol 22:17, 1975. 40. Frisch RE, and McArthur JW: Menstrual cycles: fatness as a determinant of minimum weight for height necessary for their maintenance or onset, Science 185:949, 1974. 41. Frisch RE: Population, food intake, and fertility, Science 199:22, 1978.
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42.
43. 44.
Infant care: Cache or carry
Frisch RE: Reply to Truswell J, Menarche and Fatness: reexamination of the critical body composition hypothesis, Science 200:1509, 1978. May RM: Human reproduction reconsidered, Nature 272:491, 1978. Ainsworth M: The development of infant-mother attachment, in Caldwell B, and Ricuitt H, editors: Review of child development research, vol 3, Child development and social
483
policy, Chicago, 1973, University of Chicago Press, pp
1-94. 45. 46.
Bowlby J: Attachment and loss, vol 1, Attachment New York, 1969, Basic Books, Inc., Publishers. Vital Statistics of the United States-1973, vol 1, Natality, DHEW, Public Health Service, Health Resources Administration, National Center for Health Statistics, Rockville, MD, 1977.
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P E D I A T R I C S
Richard W. Olmsted, E d i t o r
Infant care: Cache or carry To test the hypothesis that a characteristic infant-care pattern existed during most o f human history, contemporary hunter-gatherers in a representative sample o f world cultures were examined. Numerically coded measures of infant care revealed a uniform pattern. Mothers are the principal caregivers,, providing extensive body contact day and night and prolonged breast-feeding. When not carried, the baby o f hunter-gatherers has complete freedom of movement. Care ts consistently affectionate, with immediate nurturant response to crying. Nonetheless, in most groups, children achieve early independence and by 2 to 4 years spend more than half the time away from the mother. In the United States this pattern of carrying that endured f o r one to three million years has been replaced by one resemb#ng nesting or caching. Infants spend little time in body contact with earegivers and their movements are restricted by playpens, high chairs, or cribs. O f the minority who are breast-fed, half are weaned within a few weeks. Separate sleeping arrangements and delayed response to crying are regularly recommended. These remarkable transformations may profoundly alter infant development and maternal involvement.
Betsy Lozoff, M.D.,* and Gary Brittenham, M.D.,** C l e v e l a n d , O h i o
INFANT CARE in the United States and other industrialized countries no longer resembles that provided during most of human history. Breast-feeding has been supplanted or strikingly altered by the availability of breast milk substitutes, and infants have little contact with caregivers, sleep separately, and spend much of their day in playpens, high chairs, or cribs. The anthropologic evidence presented in this paper indicates that a very different pattern of infant care existed during most of the historyof the human species. One alteration, the abandonment of breast-feeding, has aroused widespread concern because of the effects on maternal fertility and infant health and survival/ The impact of changes in other features of infant care has not been examined, but the consequences for infant development and maternal involvement may be as profound. The presence of a characteristic pattern of infant care From the Departments o f Pediatrics and Medicine, Divisions o f Geographic Medicine and Hematology, Case Western Reserve University School of Medicine and Rainbow Babies and Childrens Hospital. Supported in part by a grant from the Rockefeller Foundation. *Reprint address: Division of Geographic Medicine, Deparfmem of Medicine, University Hospital~, Cleveland, OH 44106 **Teaching and Research Scholar of the American College of Phystcian~
478
The Journal o f P E D I A T R I C S Vol. 95, No. 3, pp. 478-483
during the course of human evolution is suggested by studies in comparative physiology.2.3 Among terrestrial mammals, species may be divided into those with extensive contact between mother and infant (the young are carried by, hibernate with. or follow the mother) and those with intermittent contact (the young are cached in secluded places or left in nests or burrows while the mother is absent for extended periods). These differences are reflected in breast milk composition and the interval between feedings. In species with intermittent contact. infants are adapted for separations by receiving their iotal nutritional requirements_ in spaced feedings during the mother's visits: milk ~" high in protein and fat. and feedings take place every two to 15 hours. A similar pattern of spaced feeding is conceivable in species with extensive maternal contact, but is not observed: feedings are frequent (every one to two hours) or essentially continuous, and milk is low in protein and fat. Even if the "continuous" feeding mammals are compared with those which nest their young and feed as frequently as every two to four hours, significant differences in milk composition remain.' Human milk is low in fal and extremely low in protein, suggesting that the human infant is adapted to frequent feeding and extensive maternal contact. Since human babies cannot follow their mothers at birth and do not hibernate with them. comparative physiology identifies the human pattern of infant care as that of carrying.
0022-3476/79/090478 +06500.60/0 9 1979 The C. V. Mosby Co.
Volume 95 Number 3
Infant care." Cache or carJy
479
Table. Frequency of selected infant care practices in hunter-gatherer and other nonindustrialized societies: Comparison with the United States
Huntergatherers n = 10 (%)
Other nonindustrial societies n = 176 (%)
9 1. Infant carried or held more than 50% of the time until age of trawling (3a:4-5) 2. Mother is principal caregiver in infancy (13a: 1-3) 3. Mother sleeps with the infant in same bed or room (1:5-9) 4. Generally affectionate care in infancy and in early childhood (16a & b:4-5) 5. Immediate, nurturant response to crying (5a:4-5)
100
56
Body contact 25% of the time
100 100
9O 76
Mother is principal caregiver'~ Separate sleeping recommended
100
505
No quantitative data
100
74
6. Complete freedom of movement after age of crawling (2b: 1)w 7. Infant carried with sling or no carrying device (4a: 1-3) 8. Breastfeeding for 24 months or more (ll:mean >__24 months) 9. Peer group is principal companion in early childhood (15b: 1-3) 10. Early gradual independence and autonomy (10a:3-4) 11. Child spends 50% of the time away from mother in early childhood (13b:3-5), 12. Father frequently and closely involved in early childhood (14b:4-5)1[
100
39
43% crying episodes ignored; delayed response advised Movement generally restricted
90
76
No quantitative data
86
83
6% breast-feeding at 6 mo
86
35
No quantitative data
75
70
No quantitative data
75
75
No quantitative data
75
53
No quantitative data
Infant care practices*
United States
;~Thedescriptive phrases 1 to 12 are'derived from the Barry and Paxsoncodes?~In parentheses are the column number and the ratings for which the practice was judged present. tCare often provided by unrelated individualsor institutionslike day ca~'ecenters. ~72% in infancy (16a). w age of crawling, 80% among hunter-gatherersand 25% in other non-industrialsocieties (2a:1). []In infancy, 63% among hunter-gatherersand 33% in other non-industrial societies (14a:4-5). Which h u m a n societies should be examined for a "characteristic" pattern of infant care? Industrialized societies are not appropriat e , for these have been present for a mere instant Of the species' existence: If all h u m a n history were represented by an hour, the last o n e / one-hundredth of a second would represent the 200 years of industrialization. Settled agriculture appeared only 10,000 Years (one-third of a second) ago. The mode of subsistence for over 99% of the species' two to three million-year history was hunting and gathering in the tropics. ~ 6 Therefore, data from the few surviving tropical foraging groups provide the best available indication of the care to which the h u m a n infant was adapted. 7, ~ Societies depending 'on h u n t i n g and gathering for subsistence are composed of small mobile groups, usually of 30 tO 100 people. ~ Population size is typically greatly belOw that which could be supported in a given area, .and is Stable, with babies born three to four years apart. TM The hunting of m a m m a l s provides 20% or more of the diet. 1.....
Food gathering, generally by women, supplies 40 to 60% 0f the total diet in most h u n t i n g and gathering societies. 1~ Since vegetable and anima! supplies can be exhausted if a band stays in one place t o o long, mobility is essential to this way of life. A n extreme example is provided by the !Kung San of the Kalahari Desert in Africa, who walk 3,000 miles per year? ~ This existence, even in a marginal environment, is not as arduous as might be thought. Quantitative studies have suggested that a nutritionally adequate diet may be obtained with a modest effort of two to five hours per day, leaving a substantial reserve of both h u m a n energy and environmental resource. 16-1~ Our observations'among ethnic groups in India who live primarily by hunting and gathering led us to postulate that a specific Pattern of infant care preva!led during most of h u m a n history, and would still predictably be found among present hunters and gatherers. This hypothesis Was tested bY analysis of encoded data on infant care in a representative sample of nonindustrial societies.
Lozoff and Brittenham
480
m
ioo
The Journal of Pediatrics September 1979
! I'(ung
F-no ffl
n,w m o
I
I
I
I0
20 AGE (Weeks)
30
Figure. Infant bodily contact among the !Kung San and in the United States. 9 9 = Percentage of spot observations that infant is in physical contact with caregivers among the !Kung San, redrawn from Konner8 and modified to show average of data for male and female infants. X---X = Percentage of time during continuous observations that infant is in bodily contact with the mother in the United States, from the data of Ainsworth et al.2~ During the United States observations the mother was usually the only individual having body contact with the. infant.
MATERIALS
AND METHODS
To compare infant-care patterns in the United States with those in hunting and gathering and other nonindustrial societies, anthropologic, psychologic, and pediatric sources were studied. Murdock and White's sample 2~ of 186 geographically, linguistically, and historically representative nonindustrial societies was examined. Tropical hunter-gatherers were defined as societies living between latitudes of 22030 ' N and 22030 ' S, depending primarily o n hunting and gathering for subsistence (Murdock and Morrow's Subsistence Economy,! 2 Code of S or D in Columns 5 and 6)i with less than 10% dependence on agriculture, animal husbandry, and fish!ng !Code 0, N, or U in Columns 3 and 4 a n d O or U in Column 5). Ten societies met these criteria: the IKung Bushmen, Hadza, Mbuti, Semang, Vedda, Tiwi, Siriono, Botocudo, Shavante, and Chenchu. The numerically coded measures of infant care presented by Barry and Paxson ~ were studied. These codes are based On the typical cultural practices for male middle-born children, and most are defined according to a quantitative scale from 1 to 5. Barry and Paxson ratings based on highly unreliable information or considered highly inferential were excluded. The features of infant care we scored are indicated by the descriptive phrases used in the Barry and Paxson codes (Table); the column number i n the Barry and Paxson codes is listed in parentheses along with the ratings for which the feature was judged to be present. The proportion of the huntinggathering societies in which the item of infant care was
found was calculated. The remaining 176 societies were similarly scored for the items shown. Where an alternate society was specified, the one with the most complete infant codes was chosen. Since breast-feeding schedules were not coded, descriptive accounts 8, 23-2~were examined to assess feeding frequencies. Finally, psychologic and pediatric sources 2~-37were used to determine the presence of the same features in the patterns of infant care in the United States. RESULTS
AND INTERPRETATIONS
A consistent pattern of infant care is found among the hunter-gatherers (Table). The aspects of care listed as numbers 1 to 9 in the Table are found in all the foraging societies, or in all with a single exception. In hunting and gathering societies infants are carried or held more than half the day until the age of Crawling. Infants are carried in close body Contact, either with no carrying device or with a sling or flexible Pouch, allowing the infant to mold to the mother's body. While carrying babies, the women gather food, a typically female activity which supplies about half the diet in most foraging societies. Infant carrying is thus compatible with women's work. The mother is always the principal caregiver, contact is extensive, day and night, and breast-feeding is prolonged (-->24 months). CarefUl observations among the !Kung document essentially continuous nursing, 8 and at least frequent breast-feeding on demand is reported for other societies.~3-2~Infant carrying does not imply restriction. When not held, the hunter-gatherer baby has complete freedom of movement except in emergencies, both in early infancy and after crawling. Care is uniformly affectionate, with a n immediate nurturant response to crying. The close responsive relationships a n d extensive body contact d 0 not seem to create overly dependent children. Autonomy 'and independence are generally early and gradual, so that by two to four years of age children spend more than half the day away from the ~ o t h e r in the company of peers. Usually the father is frequently and closely involve d with the child. To determine whether elements of the infant-care pattern among hunter-gatherers are widely practiced, the remaining 176 Societies were analyzed. These are nonindustrial societies with subsistence activities that have existed for/less than 1% o f human time: agricu!ture, herding, or; fishing. The prevalence of the selected features of infant care in these other societies is shown in the Table. In most the mother is still the principal caregiver, sleeps in the same bed or room, and breastfeeds for more than two years. Infants are likely to receive an immediate nurturant response to crying, and achieve
Volume 95 Number 3
early independence. In comparison with the nomadic hunter-gatherers, among whom carrying is universal, in only 56% of the other societies are young infants carried for more than half of the time. Extensive body contact and freedom of bodily movement are no longer provided in many of these societies. In the United States and other industrialized nations and among the urban poor of many developing countries, infants spend little time in body contact with caregivers. The Figure compares infant carrying in a United States' study with the !Kung of the Kalahari Desert. The !Kung infant is held or carried 80 to 90% of the time during the early months and 60% of the time at nine months? The United States' baby is held one-third of the time during the first three months and only 16% by nine months. 2~ Infant care has undergone further striking changes, shown in the Table. Mothers are still the principal caregivers, although institutions like day-care centers play an increasing role. Separate sleeping arrangements are the usual pediatric recommendation. 27' 2~ Of the minority of infants who a r e breasi-fed, half are weaned within a few weeks 26-3~ and only 6% continue as long as six months. 3~ Even when breast-feeding occurs, it is usually managed like bottle feeding, spaced every two to four hours. In the many hours of the day that infants are not held, their movements are often restricted by playpens, high chairs, and cribs. A restrained approach to infant demands and a delayed response to crying are generally advised. 2" In the United States' study cited above, a mean of 43% of infant crying episodes (not just momentary fussing) were ignored during the first year of life? 7 Comparable data about independence are not available. DISCUSSION Infant carrying and prolonged breast-feeding, observed among contemporary foraging societies, may have been an integral part of the regulation of population size during our species' two to three million-year history?* The birth of a c h i l d dramatically altered the mother's energy balance. She continued to participate in the group's periodic migrations and the women's daily foraging excursions, but for a two to three-year period also carried her child. Lactation required an additional expenditure of energy. Unless these new caloric needs were met by increased food intake, the required energy was drawn from maternal fat reserves. If it is true that the proportion of fat in a woman's body helps regulate the entire cycle of fertility and fecundability,~9-4~then the infant-care pattern was essential to maintain the three to four-year birth interval of hunter-gatherers, especially where infanticide and sexual practices played minor roles. By reducing the
I n f a n t care: C a c h e or carry
48 1
mother's proportion of body fat below that necessary for ovulation, the energy expended in breast-feeding and carrying a baby resulted in an extended period of postpartum infertility. Under conditions of food scarcity, the reaccumulation of fat reserves would have been even further delayed, the birth interval lengthened, and a balance maintained between environmental resources and population size. However, since scarcity has been considered rare among hunter-gatherers, 1~-19 the low fat proportions were probably not due to lack of food but to the vigorous active existence and high level of physical fitness. After the birth of a child, women may not have changed lifetime habits to collect and consume more food, and the proportion of fat would thus drop below that required for ovulation. A birth interval of three to four y e a r s allowed each infant to complete the period of maximal need for the mother 43.44 without competition from other young siblings. During this time the infant had extensive body contact with the mother, both day and night. The care provided was highly responsive and consistently affectionate, nurturant, and unrestrictive. By three to four years the child had achieved a degree of independence and autonomy sufficient to allow the mother to carry and care for a new infant. Comparison of the scoring of the remaining 176 representative nonindustrial societies with that of the hunters and gatherers shows many similarities. Carrying, extensive body contact, and unrestricted bodily movement are no longer common, but in most the mother is still the principal caregiver, sleeps in the same bed or room as the infant, and breast-feeds for two years or more. The pattern of carrying that endured for at least two million years has been replaced in the United States by one resembling nesting or caching. Infants spend little time in body contact with caregivers. In spite of the availability of medical means of contraception, the birth interval is often one to two years 46 and several infants may compete for maternal concern. Care for infants generally involves intermittent maternal attention, artificial feeding or spaced breast-feeding, restriction of bodily movement, and restraint in response to infant needs. The fact that a pattern of behavior was adaptive for most of the species' history does not necessarily imply that it continues to be so, nor that it is desirable. Data on parenting disturbances, family disruption, and mental illness among hunter-gatherers are scant; these problems may have been as common in our preagricultural past as they are in our industrial present. Nonetheless, the remarkable transformations in the pattern of infant care which have occurred in the last few hundred years may
482
L o z o f f and Brittenham
have h a d a p r o f o u n d i m p a c t o n n o r m a l infant developm e n t and n o r m a l m a t e r n a l i n v o l v e m e n t . Research on the effects of i n f a n t care is difficult and investigations of the issues raised here are especially so. Studies c a n n o t be restricted to industrialized societies; a b a b y receiving high levels o f m a t e r n a l b o d y c o n t a c t by U n i t e d States' standards would b e j u d g e d d e p r i v e d a m o n g hunter-gatherers. In spite of the difficulties, such research seems crucial for the choice of future p a t t e r n s o f i n f a n t care: cache or carry.
REFERENCES
1. Knodel J: Breastfeeding and population growth, Science 198:1111, 1977. 2. Blurton Jones N: Comparative aspects ~of mother-child contact, in Blurton Jones N, editor; Ethological studies of child behaviour, London, .1972, Cambridge University Press, p p 305-328. 3. Ben Shaul D: The composition of the milk of wild animals, Int Zoo Year Book 4:333, 1962. 4. Lozoff B, Brittenham GM, Trause MA, KenneU JH, and Klaus MH: The mother-newborn relationship: Limits of adaptability, J PEDIATR 91 : 1, 1977. 5. Lee RB, and DeVore I: Man the hunter, Chicago, 1972, Aldine Publishing Company. 6. Lee RB, and DeVote I: Kalahari hunter-gatherers, Studies of the !Kung San and their neighbors, Cambridge, 1976, Harvard University Press. 7. Konner MJ: Aspects of the developmental ethology of a foraging people, in Blurton Jones N, editor: Ethological studies of child behavior, London, 1972, Cambridge University Press, pp 285-304. 8. Konner M J: Maternal care, infant behavior and development among the !Kung San, Kalahari hunter-gatherers, Lee RB, and DeVore I, editors: Studies of the !Kung San and their neighbors, Cambridge, 1976, Harvard University Press. 9. Hassan FA: Determination of the size, density and growth rate of hunting-gathering populations, in Polgar S, editor: Population, ecology and social evolution, The Hague, 1975, Moulton Publishers, pp 27-52. 10. Dumond DE: The limitation of human population: a natural history, Science 187:713, 1975. 11. Angel LJ: Paleoecology, paleodemography and health, Population, in Polgar S editor: Ecology, and social evolution, The Hague, 1975, Moulton Publishers, pp 167-190. 12. Callen EO: Dietary patterns in Mexico between 6500 BC and 1580 AD, in Smith CE, editor: Man and his foods, University, Ala., 1973, University of Alabama Press, pp 29-49. 13. Isaac G: The diet of early man: aspects of archaeological evidence from lower and middle pleistocene sites in Africa, World Areheol 2:278, 1971. 14. Lee RB: What hunters do for a living, or, How to make out on scarce resources, in Lee RB, and DeVore I, editors M a n the hunter, Chicago, 1968, Aldine Publishing Company, pp 30-48. 15. Martin MK, and Voorhees B: Female of the species, New York, 1975, Columbia University Press.
The Journal o f Pediatrics September 1979
16. Lee RB: Mongongo: the ethnography of a major wild food resource, Ecol Food Nutr 2:307, 1973. 17. McCarthy D, and McArthur M: The food quest and the time factor in aboriginal economic life, in Mountford CP, editor: Records of the Australian-American expedition to Arnhem land, Vol 2, Anthropology and nutrition, Melbourne, 1960, University Press, p 181. 18. Wehmeyer AS, Lee RB, and Whiting M: The nutrient composition and dietary importance of some vegetable food eaten by the !Kung Bushmen, S Afr Med J 43:1529, 1969. 19. Sahlins M: Stone age economics, Chicago, 1972, Aldine Publishing Company. 20. Murdock GP, and White DR: Standard cross-cultural sample, Ethnology 8:329, 1969. 21. Murdock GP, and Morrow DO: Subsistence economy and supportive practices: cross-cultural codes 1, Ethnology 9:302, 1970. 22. Barry H, and Paxson L: Infancy and early childhood: cross-cultural codes 2, Ethnology 7:466, 1968. 23. Holmberg AR: Nomads of the long bow. The Siriono of Eastern Bolivia, New York, 1969, Natural History Press. 24. Maybury-Lewis D: Akwe=Shavante society, New York, 1974, Oxford University Press. 25. Jelliffe DB, Woodburn J, Bennett F, and Jelliffe EFP: The children of the Hadza hunters, J PEDIATR 60:907, 1962. 26. Blehar MC, Ainsworth MD, and Bell SM: Developmental changes in the behavior of infants and their mothers relevant to close bodily contact (monograph in preparation). 27. Vaughn VC, and McKay RJ, editors" Nelson textbook of pediatrics, Philadelphia, 1975, WB Saunders Company, p 217. 28. Spock B: Baby and child care, New York, 1976, Pocket Books. 29. Sloper K, McKean L, and Baum JD: Factors influencing breast feeding, Arch Dis Child 50:165, 1975. 30. Davies DP, and Thomas C: Why do women stop breast feeding? Lancet 1:420, 1976. 31. Bax CO, and Hart H: Encouraging breast-feeding, Lancet 2:1214, 1976. 32. Coles EC, Cotter S, and Valman HB: Encouraging breastfeeding, Lancet 2:978, 1975. 33. Report of new mothers survey, Data on file at Ross Laboratories, 1975. 34. Harfouche JK: The importance of breast-feeding, J Trop Pediatr 16:133, 1970. 35. Sjolin S, Hofvander Y, and Hillervik C: Factors related to early termination of breast feeding, Acta Paediatr Scand 66:505, 1977. 36. Fomon SJ: What are infants fed in the United States? Pediatrics 56:350, 1975. 37. Bell SM, and Ainsworth MDS: Infant crying and maternal responsiveness, Child Dev 43:1171, 1972. 38. Howell N: Toward a uniformitarian theory of human paleodemography, J Human Evol 5:1, 1976. 39. Frisch RE: Demographic implications of the biological determinants of female fecundity, Social Biol 22:17, 1975. 40. Frisch RE, and McArthur JW: Menstrual cycles: fatness as a determinant of minimum weight for height necessary for their maintenance or onset, Science 185:949, 1974. 41. Frisch RE: Population, food intake, and fertility, Science 199:22, 1978.
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Infant care: Cache or carry
Frisch RE: Reply to Truswell J, Menarche and Fatness: reexamination of the critical body composition hypothesis, Science 200:1509, 1978. May RM: Human reproduction reconsidered, Nature 272:491, 1978. Ainsworth M: The development of infant-mother attachment, in Caldwell B, and Ricuitt H, editors: Review of child development research, vol 3, Child development and social
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Bowlby J: Attachment and loss, vol 1, Attachment New York, 1969, Basic Books, Inc., Publishers. Vital Statistics of the United States-1973, vol 1, Natality, DHEW, Public Health Service, Health Resources Administration, National Center for Health Statistics, Rockville, MD, 1977.
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