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Correlates of breastfeeding frequency among nomadic pastoralists of Turkana Kenya A retrospective study.

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Correlates of Breastfeeding Frequency Among Nomadic
Pastoralists of Turkana, Kenya: A Retrospective Study
Department of Anthropology, University of Kansas, Lawrence, Kansas
Reproductive ecology, Breastfeeding patterns,
Breastfeeding structure, Lactational amenorrhea, Infant growth
Recent research has shown that significant variation in
breast-feeding behavior exists among natural fertility populations, all of
whom have been characterized as practicing “on-demand breastfeeding. A
number of recent prospective studies have contributed to a better understanding of breastfeeding structure and of its consequences for population differences in fertility. Currently, there is a growing interest in quantifying the
complex environmental and biocultural interactions which influence that
structure; in other words, in establishing an ecology of breastfeeding.
In this paper, a carefully structured retrospective study of breastfeeding
behavior among nomadic Turkana is used to identify environmental, biobehavioral, and socioeconomicfactors associated with variation in breastfeeding
frequency among Turkana women. In agreement with the results of a prospective study conducted as part of the same research, the age (growth) and
physical development of nurslings show significant correlations with
breastfeeding frequency. Maternal physical status, the depth of the maternal
social network, and, t o a lesser degree, rainfall patterns are also significant.
All of these factors appear to influence breastfeeding through their effects
on maternal participation in herding activities and related absences from
camp. Finally, the study also presents new strategies for collecting and utilizing retrospective data, which are notoriously unreliable and difficult to classify
accordingto operational definitions recently developed for prospective studies.
Results of the present study suggest methods by which the quality and reliability of recall data may be enhanced. o 1995 Wiley-Liss, Inc.
In 1989, a study of reproductive biology
and behavior of Ngisonyoka pastoralists of
South Turkana, northwest Kenya, was initiated to determine causes of the extreme seasonality of births observed in that population
(Leslie and Fry, 1989). Among factors hypothesized to affect the timing of births and
conceptions were seasonal variation in the
nutritional status of Turkana women, in the
timing of initiation of weaning and resumption of menses postpartum, and in infant
mortality. Since breastfeeding and weaning
practices may have a significant effect on
any or all of these parameters, a study of
infant care and feeding practices among Ngisonyoka was undertaken between May 1989
and late February 1990 (Gray, 1992).
In addition to quantifying effects of lactation on birth seasonality, an important objective of the infant feeding study was to develop an ecology of breastfeeding among
nomadic Turkana. Our objective was, on the
one hand, to quantify the duration of lacta-
Received November 12, 1993; accepted May 18, 1995.
Address reprint requests to Sandra J. Gray, Dept. ofhthropology, 622 Fraser Hall, KU, Lawrence, K S 66045.
tion and the structure of breastfeeding, since
those two parameters were assumed to be
directly linked to fertility patterns. On the
other hand, we wished to identify the environmental, cultural, and biological interactions influencing lactation and breastfeeding in this population. I n this paper, the focus
is on the second of those two objectives. Specifically, the study examines the effects of
selected environmental and biobehavioral
factors on breastfeeding structure among
nomadic Turkana. In order to contextualize these effects, brief discussions of the
model used to design the research and of
breastfeeding structure in this population
are also included.
Turkana District is located in the northwest corner of the Republic of Kenya, between 1'0 and 5'0 north latitude (Fig. 1).
The area is semiarid to arid scrub savanna
and is subject to marked periodicity in rainfall. In the ideal, rainfall is distributed in a
bimodal pattern across the year: the longer
rainy season lasts from the end of March
through the end of May and is followed by
a long dry season, which begins toward the
end of July. The dry season may be punctuated by the short rains (erupe) in October
or November. In actuality, the timing of the
rains and the amount of rainfall at any given
locale in Turkana vary dramatically from
year to year. Drought is a frequent occurrence and may be anticipated at least once
during a 5 year period, although it is impossible to predict precisely when. During
drought, some rain may fall, but the pattern
is generally one in which there is a violent
storm during one isolated month but little or
no rain in the preceding or following months.
During the last 15 years, there have been
three droughts of varying severity: one from
1979-1981, another from 1984-1985, and
the most recent one lasting from March 1990
through the beginning of 1992. However, the
rains during the year of the breastfeeding
study were described by nomadic Turkana
as good.
Lamphear (1992) includes Turkana people
among the Karimojong linguistic cluster,
and Vossen ( 1982) classifies Teso-Turkana-
speaking peoples as part of the Eastern Nilotic language group (Nilo-Saharan:ChariNile)(see also Greenberg, 1966). The members of the Ngisonyoka subsection of South
Turkana, who were the focus of the South
Turkana Ecosystem Project (STEP), are primarily nomadic pastoralists, keeping mixed
herds of camels, cattle, sheep, goats, and
donkeys and moving their animals frequently in response to resource availability,
the season of the year, the severity of the
dry season, and the prevalence of livestock
diseases in a particular area.
Vegetation is sparse and is patchily distributed across South Turkana. Acacia ssp.
and thorn scrub are the predominant species, but there are also areas in which various species of grasses may also be found,
depending on the rainfall. Water for the
herds is obtained from wells which are dug
in the dry washes that crisscross the region.
Herders move their livestock as the need for
forage and water demands. During the dry
season, vegetation becomes increasingly
scarce, while water may be quite distant
from forage. To distribute foraging stress
more evenly throughout their territory, large
herding units are broken down into smaller
satellite herds, which are then sent to different parts ofthe range (Ellis and Swift, 1988).
Because longer distances must be travelled
between wells and forage, and because there
are fewer people in each herding unit, labor
demands on individuals tend to be more intense during the dry season than during the
rainy season.
Since the pastoral system is labor-intensive, wives and children contribute substantially to the labor pool. Successful, wealthy
herders are those men who possess large
herds and many people to tend them. These
may include several wives, many children
of varying ages, and other members of a n
extended social network. Rada DysonHudson (1989) described the subsistence
strategy as one in which both herd size and
family size are optimized. In such a socioeconomic context, the value placed on children
is high, and Ngisonyoka women average
seven live births by the end of their reproductive years (Brainard, 1981; Leslie and Fry,
1989; Gray, 1992).
Major features of the environment and of
24 1
Fig. 1. Map of South Turkana
the pastoral system have been described in
detail in several publications (see Coughenour et al., 1985; Dyson-Hudson and
McCabe, 1985). Health, biology, and demography of Ngisonyoka were examined in studies undertaken during the 1980s and early
1990s (Mugambi and Little, 1983; Leslie e t
al., 1988; Little et al., 1988; Leslie and Fry,
1989; Little and Gray, 1990; Little, in press).
Results of recent studies of human reproduc-
tion in South "urkana may be found in Leslie
e t al. (1993).
The model used to design the research is
shown in Figure 2. Since rainfall patterns
and seasonality have been associated with
human biology of nomadic Turkana in sev-
r - - - - - - - - - - - - - - - - - - -1
.c --c
- --
Fig. 2. Environmental, biological, socioeconomic, and behavioral factors hypothesized to influenced
breastfeeding behavior among nomadic Turkana pastoralists.
era1 earlier studies, they were given a primary causative position in the research design. However, rainfall effects were assumed
to be mediated by other biobehavioral factors
affecting both mothers and their nurslings.
These factors, shown as biological, social,
and behavioral components in Figure 2, have
figured prominently in previous studies of
nutrition and dietary practices in Turkana
(see Wienpahl, 1984; Galvin, 1985).
The two major components of breastfeeding behavior are defined as outcome variables in the model: breastfeeding structure
and duration of lactation. Breastfeeding
structure is defined by Vitzthum (1994a, p.
309) as “the temporal patterning of suckling
duration and frequency.”Although effects on
fertility of the duration of lactation have
been known for some time (see Bongaarts,
1981),only recently have scientists begun to
understand the impact of daily breastfeeding structure (McNeilly et al., 1988). It is
now clear that this structure varies markedly among so-called natural fertility populations (Campbell and Wood, 1988),with important consequences for population
differences in the timing of the resumption
of menses postpartum and of the length of
interbirth intervals (Gray, 1994a; Vitzthum, 1994a).
The model presented here builds upon the
work of several researchers. Popkin et al.
(1986) developed a similar research framework which incorporated maternal, infant,
and household factors as determinants of infant care and feeding practices. Jones (1988,
19901, applying the results of research by
McNeilly et al. (19881, used multiple hazards analysis to demonstrate the effects of
both breastfeeding structure and the duration of lactation on the timing of the return
to menses postpartum. Vitzthum (1989) and
Wood et al. (1985) showed that components
of individual breastfeeding bouts (the intervals between bouts and the duration of suckling during bouts) may be determined by
quite different sets offactors and must therefore be treated independently in analysis.
The work of Panter-Brick (1991) and Vitzthum (1988) successfully integrated cultural
variables such as labor demands on mothers
and economic change into analysis of factors
affecting infant feeding practices.
The model also draws heavily on results
of studies carried out by the members of the
South Turkana Ecosystem Project (STEP), a
long-term, multidisciplinary study of human
ecology which was initiated in the late 1970s.
Independent variables considered here are
those that have been demonstrated to play
key roles in several aspects of human biobehavioral adaptation in South Turkana (Little, in press). From the onset, it was assumed
that these same variables would influence
decisions relating to the care and feeding of
young children. Furthermore, it was hypothesized that care of the youngest and most
vulnerable people in Turkana society would
be best understood as yet another set of coping strategies in this arid and unpredictable
environment. Given the variable ecological
context in Turkana, however, a preliminary
caveat is in order: infant feeding and caretaking behaviors reported here should be
viewed as representative of the social and
environmental conditions prevailing at the
time of the study.
tween episodes suggested two distinct temporal patterns: in one pattern, episodes were
separated by less than 15 min, on average,
and, in the second, interepisode intervals
were significantly longer.
It appeared that Turkana children suckled
almost constantly during periods of close
maternalhursling interaction. During these
periods, which might last 1-2 h, children
were breastfed whenever they demanded the
nipple, regardless of their age (in fact, children older than age 15 months were the most
demanding of the breast). It was also the
case, however, that several hours of intense
breastfeeding activity might be preceded
(or followed) by several hours in which
no breastfeeding occurred. These nonbreastfeeding intervals among Turkana
Breastfeeding patterns among
women ranged from 1 or 2 h to the entire
nomadic Turkana
day, from sunrise to sundown.
The breastfeeding study included both
Since the length ofintervals between suckprospective and retrospective components. ling activity is a key factor in the return of
Results of the prospective component were lactating women to prepregnant hormonal
presented in detail in Gray (1994a), in which levels and thus in the duration of postparcomparison of breastfeeding structure tum amenorrhea (McNeilly et al., 1985,
among Gainj of New Guinea (Wood et al., 1988; Vitzthum, 1994b), it was hoped that
19851, Quechua of Peru (Vitzthum, 1989), an understanding of the ecology of
and Turkana was undertaken. To facilitate breastfeeding among nomadic Turkana
comparison with those studies, temporal would explain this bimodal structure and, by
patterns of suckling activity were defined as extrapolation, the influence of breastfeeding
in Vitzthum (1989) and Wood et al. (1985). practices on fertility and birth seasonality
A nursing event was recorded any time the in this population.
child took the nipple into its mouth. Events
were clustered into episodes: a series of
events separated from each other by less
than 5 seconds. A breastfeeding session conThe small sample size of the prospective
sisted of a series of episodes separated from sample (N = 231, however, limited its useeach other by less than 60 seconds.
fulness in elucidating ecological relationThe most meaningful statistical unit of ships, and a decision was made to use the
breastfeeding activity among nomadic Tur- larger retrospective sample. The retrospeckana was the nursing episode. Suckling ac- tive component of the study included 101
tivity was not clustered into well-defined motherhursling pairs. Of the 101 women
sessions (a series of closely spaced episodes), in the study, 92 were able to reconstruct
as had been observed by Vitzthum among their activity schedules (and hence their
Quechua women (1989), but occurred in- breastfeeding schedules) for the previous
stead as a series of isolated episodes, usually day with some precision. Information prolasting no more than 2 or 3 min but sepa- vided by these women was corroborated by
rated by intervals longer than l min (for a other women in the herding camp or by their
nice illustration of this pattern, see Fig. 1 in husbands. Nine women were either uncerVitzthum, 1994a). The frequency of suck- tain about the timing of some events during
ling increased dramatically as children ap- a 1-3 h period or were judged to be poor
proached the second half of their second year. informants, and their responses were exFurthermore, analysis of the intervals be- cluded from analysis.
TABLE 1. Age structure of the samples of mothers and
nurslings in the n r k a n a breastfeeding study:
Retrospective component
A. Age and panty of mothers in the retrospective study
Aee class
Mean age
Mean parity
21-30 years
3 1 4 0 years
Over 40 years
26.1 (0.389)
34.2 (0.455)
44.0 (1.155)
2.2 (0.144)
4.1 (0.311)
5.5 (0.885)
30.0 (0.622)
3.0 (0.183)
B. Age and sex of nurslings in the retrospective study
Age class
Less than 1 month
1-3 months
4-6 months
7-9 months
10-12 months
13-15 months
1&18 months
19-21 months
Over 24 months
Mean age, months (s.e.1
8.3 (0.886)
7.5 (0.778)
Subjects were selected to include women
throughout the female reproductive span,
and parity ranged from 1-9. Nurslings were
selected to include equal numbers of both
sexes and to represent a cross-section of ages
from birth through the second year. Since
Turkana do not keep records of birth dates,
ages of women were estimated using a South
Turkana event calendar developed by Rada
Dyson-Hudson, Paul Leslie, and Eliud Lowoto. More precise birth dates were provided
for nurslings, since mothers were often able
to recall the exact month of the birth. Estimated age structure of the sample is shown
in Table 1.
During a detailed preliminary interview,
each woman was asked to recall her
breastfeeding and activity schedule, her own
dietary intake, and intake of nonbreastmilk
foods by her nursling for the 24 h period
immediately preceding the interview. In addition, each woman and her husband assisted in reconstructing her reproductive
history. Husbands also provided information
on livestock resources and on size and composition of the herding unit (awi)as a whole,
as well as of their wives’ own households (a
woman’s household, her ekol, includes those
people whom she feeds with the milk from
her allotted milch animals). Finally, each of
the 101 women in the study was observed
at least once when she went to milk her livestock, either in the morning or the early evening of the day of the interview. At that time,
the number of her milch animals and the
quantity of milk produced by each species
were recorded. These data were used to verify information provided during the interview in order to estimate as precisely as possible the socioeconomic ranking of the awi.
The use of retrospective data of suckling
activity posed a number of methodological
problems, which have been discussed recently by Vitzthum (1994b). However, recall
data collected during the Turkana study differed somewhat from the type discussed in
that paper. Thus, additional-and
important-research questions in this study
pertain to the usefulness and reliability of
recall data of the type collected in Turkana
and to the adequacy of those data for identifying sources of variation in breastfeeding
structure among nomadic Turkana.
In the initial days of the study, mothers
were simply asked to report how many times
they had breastfed during the preceding 24
h and how long their nursling suckled during
each feed. As has been true of other studies
(Vitzthum, 1994b), these were completely
unrealistic questions and were considered
quite impossible by the women in the study
(who were always ready to express their attitude concerning the inquiry at hand), since
Turkana children were given the breast so
frequently. Although they could not provide
an actual count of individual suckling episodes, mothers were able to recall when during the day they experienced periods of frequent suckling activity. These periods were
punctuated by children’s naps or by mothers’
leaving their children for one or more hours
to go to the well, to town, or to visit a neighboring awi. Activities occupying less than an
hour included collectingfirewood or milking.
Mothers were able to recall the time and
duration of their activities with considerable
precision by referring to the position of the
sun or to some other event for which the
time could be reliably estimated. It became
clear that the best way to obtain recall data
on breastfeeding structure was for mothers
to reconstruct their activity schedules for the
TABLE 2. Actiuitv patterns of nomadic Thrkana women bv time of day
Time of day
Observation period
Early morning (before sunrise)
4:OO AM to 7:OO AM
7:OO AM to 11:OO AM
11:OO AM to 4:OO PM
Late afternoon
4:OO PM to 7:OO PM
9:00PM to 4:OO
to 9:00PM
Characteristic activity
Rising, building fire, milking animals; breastfeeding between
and during tasks
Prepare morning meal, make buttermilk and butterfat, look
after baby animals, assist men as they move herds from
kraals, domestic tasks; depart to herd or water animals,
travel to town or to neighboring camps; breastfeeding
between and during tasks
Domestic tasks, such as beadwork, making clothing, rest or
sleep in the cool of the ekol, visit with other women in the
awi; water or graze animals; nurslings often nap at this time
or visit the ekol of a female relative
Women gather firewood, other tasks near camp; animals
return to camp (camels and cattle first); women begin
milking; small stock return to camp, with herders; herding of
animals into kraals; young stock returned to mothers; very
busy; nurslings usually carried on their mothers’ backs
during these tasks
Milk small stock; cook evening meal; talk and storytelling,
visit neighbors; dancing and singing (wet season);
breastfeeding between and during tasks
Sleep with nursling a t breast; in the dry season, women may
depart with baby animals to take them to water
entire 24 h period. These schedules proved
to be consistent with the daily pattern of
breastfeeding and work observed during
the prospective component of the study
(Table 2). In addition to estimates of 24 h
breastfeeding frequency and of the number
of hours in which no breastfeeding occurred,
maternal recall of activities was used to determine labor demands of the pastoral system on mothers, the degree to which mothers
relied on alternative caretakers, and the pattern of weaning.
In order to determine whether there was
diurnal variation in suckling activity, the
day was divided into six periods derived from
maternal work and sleep patterns observed
during the prospective study: very early
morning, from approximately 4:OO AM until
sunrise, at about 7:OO AM; morning, from
sunrise to 11:OO AM; midday, from 11:OO AM
to 4:OO PM; late afternoon, from 4:OO PM until
sunset a t approximately 7:OO PM; evening,
from sunset until bedtime a t about 9:00 PM;
and night, from bedtime until early morning,
when mothers awoke (Table 2).
Other data obtained during interviews
were used to quantify biological, socioeconomic, and behavioral factors hypothesized
to influence breastfeeding behavior (Fig. 2).
Household and livestock data were used in
computing three socioeconomic indices: the
socioeconomicrank of the herding camp, the
depth of the woman’s social network, and
the number of her cowives. The ranking was
calculated from counts of adults and adolescents in residence, estimates of herd size and
composition, and counts of milch animals in
the herd. Since livestock resources and human resources in Turkana are linked, camps
which had more livestock also had more
adults and adolescents in residence (adolescents are responsible for watering and herding the livestock, relieving married women
from these tasks); hence, they were of higher
socioeconomic ranking. Lower-rank camps
might consist of one herder with one wife,
one older postreproductive woman, several
children under age 5 years, and a few animals, usually goats, sheep, and one or two
camels or cows. The ranking of the awi was
used as both a n indicator of the overall economic status and self-sufficiency of the herding unit and as a n estimate of its resilience
to the stresses ofthe dry season: food scarcity
and increased energetic demands on both
humans and livestock associated with longer
distances travelled between wells, grazing
areas, and camp sites. A detailed discussion
of socioeconomic differences in this sample
may be found in Gray (1994b).
The number of close family or friends not
in residence in the camp a t the time of the
study but with whom a woman reported frequent interactions (several visits over the
course of a year) was used a s a n index of the
depth of her social network. The number of
cowives includes only those who resided in
the same herding camp as the woman herself; otherwise, they are included as members of the external network. The depth of
the social network and the number of a woman’s resident cowives were used as measures
of human resources: specifically, the number
of people who were available to assist in child
care and herding responsibilities and to provide additional food, animals, or money
(Wienpahl, 1984; Gray, 1994b).
Anthropometric examinations of all mothers and their nurslings were conducted on
the same day as the interview. These data
were used to assess nutritional status, size,
and body composition of mothers and their
nurslings. Measurements included recumbent length, head and chest circumferences
(children only), height (of mothers), weight,
midcalf and upper arm circumferences, and
six skinfolds (triceps, suprailiac, subscapular, periumbilical, midaxillary, and midcalf).
Maternal stature was measured to the nearest millimeter using a standard anthropometer. Recumbent length was measured to
the nearest millimeter using a n infant measuring board. Children were weighed in a
basket suspended from a Salter metric scale.
If they were too big for the basket, they were
weighed on a Health-0-Meter floor scale. In
some cases, mothers of children who resisted
weighing were asked to step on the scale
holding the child, and the measurement was
recorded. The child was then taken from the
mother, who was weighed again. The difference in the two weights was recorded as the
weight of the child. Maternal weight was
measured using a Health-0-Meter floor
scale and was corrected for the weight of
clothing and adornment. All weights were
measured to the nearest 0.1 kg. All circumferences were measured to the nearest millimeter using a plastic-coated cloth measuring
tape. Skinfold measurements were taken to
the nearest mm using a Lange skinfold
Monthly rainfall data were obtained from
the meteorological station at the district capital in Lodwar and represented the monthly
average of five locations across Turkana (two
are in South Turkana). Rainfall influences
availability of forage and distances travelled
between forage and water; hence, it affects
labor and energetic demands on all members
of a herding unit.
Dependent variables, as used in this paper,
refer to reported frequencies of breastfeeding activity. For each motherlnursling pair,
these include individual counts for each time
of day described in Table 2 above a s well as
the summed count for the entire 24 h period.
Independent variables refer to factors hypothesized to influence breastfeeding behavior: rainfall, all maternal and infant characteristics, and all socioeconomic indices.
However, the designations dependent and independent as used here should not necessarily be assumed to suggest causality; they are
used rather to simplify discussion. The term
bouts, when used in this paper, refers to extended periods of on-demand breastfeeding
as reported by mothers during 24 h recall
interviews. It is used with the specific purpose of differentiating recalled breastfeeding
data from prospective data; since neither the
frequency nor duration of suckling episodes
during these bouts was known, it was felt
that the use of the suckling unit session (as
defined by Vitzthum, 1989) to describe such
activity was inappropriate.
Univariate analysis was run for all dependent and independent variables. Of these,
only anthropometric variables were normally distributed. Factor analysis (Bernstein e t al., 1988) was used to identify intercorrelations and underlying factors in
anthropometric data.
Most of the data collected for the study
were counts (with the exception of anthropometric data), but attempts to normalize
them using a square root transformation
(Sokal and Rohlf, 1981) were unsuccessful.
Failure of the data to satisfy the assumptions of parametric analysis clearly indicated that nonparametric analysis was more
appropriate for this study. Two measures of
rank-sum association were employed:
Spearman’s coefficient of rank-sum correlation and the Kruskal-Wallis X2-approximation to test for differences in location of
ranked data. Where only two classes were
considered, the Wilcoxon 2-sample rank sum
test of differences in central location (normal
4 5 6 7 8 9101112 1 2 3 4 5 6 7 8 9101112 1 2 3 4
Time of day
Fig. 3. Variation in frequency of breastfeeding bouts reported by nomadic Turkana women by time
of day.
approximation) was used (Sokal and Rohlf,
Statistical analyses were undertaken using SAS/STAT, Version 6.0, fourth edition.
PROC UNIVARIATE was used for univariate analysis; PROC PRINCOMP and PROC
FACTOR were used for exploratory analysis
of anthropometric data. PROC FREQ and
PROC CORR were used to identify associations between variables; PROC NPARlWAY
was used for nonparametrie analysis of
A total of 639 bouts of suckling activity
were reported by the 92 women. As is discussed in detail below, there was variation
in absolute frequencies of suckling activity
among the mothers in the study. Nonetheless, a clear diurnal pattern emerged which
was consistent across all women in the sample, regardless of the frequency with which
they nursed their infants (Fig. 3). Approximately 34% of all bouts were reported to
have occurred in the 7 h from 4:OO AM t o
11:OO AM. Nearly 16%occurred in the early
evening hours, between 7:OO PM and 9:00 PM.
Twenty-five percent occurred during the
night, and 25% of bouts occurred in the 8
midday and late afternoon hours, between
11:OO AM and 7:OO PM. Mothers were more
likely to report that they had experienced
more than one bout during morning or nighttime hours. The frequency of nighttime
bouts was certainly underestimated, since
mothers consistently reported that they did
not always wake when their children nursed
during the night (children slept a t their
mother’s breast). Furthermore, mothers
were more likely to report that they had not
nursed at all during midday or late afternoon
hours. The total number of feeds reported for
the 24 h period was most strongly correlated
with the frequency of breastfeeding activity
in morning and nighttime hours (Table 3).
Correlation analysis was run to identify
associations between bout frequency and the
independent variables described above. Statistically significant correlations are shown
in Tables 4 and 5. Correlations were gener-
TABLE 3. Spearman coeficients (r,) of correlations between the total number of breastfeeding bouts reported by Turkana
women for 24 h and breastfeeding bouts reported for each time of day
Total number of
breastfeeding bouts
TABLE 4. Spearman coeficients (rJ of correlations
between biological, socioeconomic, and behavioral
factors and 24 h breastfeeding frequency as recalled
bv Turkana women'
Number of
bouts (24h)
Maternal weight
Maternal sum of six skinfolds
Age of nurslings
Nursling head circumference
Nursling midaxillary skinfold
Depth of social network
Hours mothers and nurslings
were apart
Rainfall in month of interview
Hours with
no bouts
= 0 < 0.05
'Association is independent of maternal age or parity or infant age.
3Association is independent of infant age or growth.
'0.05 c P < 0.1.
TABLE 5. Spearman coefficients (r,) of correlations
between socioeconomic and behavioral uariables and
frequency of breastfeeding bouts by time of day as reported
bv nomadic Thrkana women
Wife number
Number of cowives in
Depth of social network
Number of hours apart
Rainfall in the month of
' P Ir,l = 0 < 0.05.
' P jr,I = 0 c 0.001.
'0.05 < P < 0.1.
ally weak but tended to be stronger for the
total number of bouts in the 24 h period (Table 4) than for the number of bouts during
a particular time of day. Exceptions were the
number of bouts during the morning and
midday periods with the number of hours
mothers spent apart from their infants
(r8= -0.37 and -0.44, respectively; P <
0.001) and the number of nighttime bouts
with several of the socioeconomic indices
(Table 5). The total number of bouts was
significantly correlated with several mea-
sures of child growth, but these associations
were not independent of nursling age, which
was itself only weakly associated with 24 h
bout frequency. The strongest association of
bout frequency with any growth variable
was with head circumference, but this association was independent of the age of the
child (partial r, = -0.26; P = 0.013). Interestingly, there was no significant relationship between bout frequency and fatness of
infants (which had been shown to be independent of age and growth in preliminary
factor analysis). Of maternal characteristics,
weight and the sum of six skinfolds showed
the strongest associations with the reported
frequency of breastfeeding bouts. Both associations were independent of any measures
of maternal or infant age. Indeed, preliminary principal components analysis had
shown that these two variables were the best
indicators of maternal size and fatness, respectively.
Of the other independent variables, only
the depth of the social network and the number of hours mothers spent away from their
infants were significantly correlated with
the 24 h frequency of breastfeeding bouts.
Rainfall showed a very slight association
with 24 h bout frequency (Table 41, most
probably an artifact of its slightly stronger
association with the frequency of nighttime
bouts (Table 5).
Given the nature of these data, it was impossible to obtain estimates of the duration
of suckling during bouts; however, estimates
of the number of hours individual mothers
went without breastfeeding could be calculated from periods of the day for which they
reported no bouts. Correlations between
these estimates and the set of independent
variables were run; those results are also
shown in Table 4. There were no significant
associations of the number of hours in which
mothers failed to breastfeed with nursling
age or growth. However, there was a correlation with the fatness of children, as measured by the midaxillary skinfold; as had
been suggested by the results of principal
components analysis, this association was
independent of nursling age. Of the maternal characteristics, maternal fatness (the
sum of six skinfolds) was significantly and
independently correlated with the number
of hours in which no breastfeeding occurred.
To summarize, bout frequency was positively correlated with the size and fatness
of mothers and the depth of their social network but negatively correlated with age
(growth) and head circumference (independent of age) of nurslings. There was a strong
negative correlation between bout frequency
and the number of hours mothers spent
apart from their nurslings and a slight negative association with rainfall in the month
of the interview. Failure to breastfeed during
part of the day, on the other hand, was negatively correlated with both maternal and
nursling fatness but positively correlated
with the number of hours mothers and nurslings were apart. All associations, although
statistically significant, were relatively
In a n effort to clarify associations suggested by the results of correlation analysis,
nonparametric analysis of variance in bout
frequency was undertaken. On the basis of
the results of univariate analysis, women in
the sample were assigned to one of three
groups: those mothers who recalled nine or
more bouts during 24 h (those above the seventy-fifth percentile; N = 20), those who recalled between six and eight bouts (N = 48),
and those who reported five or fewer bouts
(those below the twenty-fifth percentile;
N = 24). Although the three groups exhibited similar patterns of breastfeeding activity over the course of the day (see Fig. 3),
women in the low-frequency group were
more likely to report that they had failed to
breastfeed a t all during a given period of the
day (for 36.1% of all periods recalled, they
reported no suckling activity). Furthermore,
they tended to report only one bout per period in which they did breastfeed (Table 6).
Women in the high-frequency group recalled
very few periods in which they failed to
breastfeed (9.2%of periods recalled) but sev-
eral periods in which they experienced two
or more bouts (47.5% of periods). Women in
the median frequency group generally reported breastfeeding activity similar to that
of the high-frequency group but recalled very
few periods in which three or more bouts
occurred (3.5%of periods recalled).
All of the women in the low-frequency
group reported that they had failed to
breastfeed during a t least one period of the
day, and 71% (N = 17) reported failure to
breastfeed during two or more periods. Of
these, 50%(N = 10)experienced two or more
consecutive periods without breastfeeding.
Since the majority of nonnursing periods reported by these women were clustered into
two or more blocks of time in the morning,
daytime, and early evening hours, it is certain that they had experienced interbout intervals in the range of 5-10 h in the preceding 24 h period.
Among the other women in the study, the
percent not breastfeeding during at least one
period of the preceding 24 h was 50% and
63% for high-frequency and mediumfrequency feeders, respectively. Only one
woman from the high-frequency group failed
to nurse during two or more periods (5%);
these were consecutive blocks of time. Of the
women in the median-frequency group, 21%
(N = 10) failed to nurse during two or more
periods; of these, five women experienced
two consecutive periods with no suckling activity (10% of median group).
Nonparametric analysis of variance
(Kruskal-Wallis X2-approximation) was run
for each of the variables that were correlated
with bout frequency and failure to breastfeed
(in Tables 4, 5). The exception is infant
weight, which was included because of its
high correlation with growth. Results are
shown in Table 7. The analysis allows more
precise characterization of each of the three
groups of motherlnursling pairs. Mothers in
the low-frequency group weighed less and
tended to be shorter than the mothers in the
other two groups. Their social network was
more shallow, and they spent significantly
more hours away from their infants. The
nurslings in this group were slightly larger,
as indicated by differences of 2 cm in head
size and 1 kg in weight. They were also on
average 2.5-3 months older than the
TABLE 6. Percent of recalled periods' for which zero, one, two, or more than 2 breastfeeding bouts were reported by
Turkana women in the retrospectiue study
Number of bouts reported
0 bouts reported
1 bout
2 bouts
3 or more bouts
Total bouts reported
Total periods recalled
Ratio of boutdperiods
Likelihood Ratio Xz, testing for Row
Percent of recalled periods, by level of
breastfeeding frequency in 24 h
Column IndeDendence: 99.67. P
'Periods of the day, as described in Table 2.
TABLE 7. Results of analysis of variance between groups of Turkana women in breastfeeding activity and in biological,
socioeconomic, and behavioral factors' hypothesized to affect breastfeeding behavior: Retrospectiue study
Turkana women grouped by 24 h bout frequency
Mean number of feeds recalled (24 h )
Mean number of hours in which no bouts were
reported (24 h )
Mean number of hours in which mothers and
infants were apart
Mean infant age (months)
Mean infant weight (kg)
Mean infant head circumference (cm)
Mean infant midaxillary skinfold (mm)
Mean maternal height (cm)
Mean maternal weight (kg)
Mean infant midaxillary skinfold (mm)
Mean depth of mother's social network
Mean rainfall, month of interview
N = 24
N = 48
N = 20
P < 0.0001
P < 0.0001
P < 0.001
P < 0.0825
P < 0.029
P < 0.0546
P < 0.0796
P < 0.001
P < 0.0173
P < 0.0852
'Variables selected for analysis are those t h a t were significant in correlation analysis (Tables 5, 6). Standard errors are shown on the line
below the group mean in parentheses.
children in the other two groups, although
the age difference was not statistically significant. Children in the low-frequency
group were also slightly thinner, as indicated
by differences in midaxillary skinfold thickness. Differences between the highfrequency and median-frequency groups
were negligible and suggested that there
were in fact only two distinct groups of mothers in this study: those who reported five or
fewer breastfeeding bouts in the preceding
24 h and those who reported more than five.
In relation to variation in bout frequency
in the latter group, differences in rainfall,
although only of slight significance, are of
interest. There was an increase of approximately 8 mm rainfall in the month of the
interview for each group, moving from high
frequency to low. That is, the lowest rainfall
occurred during the months in which the
women in the high-frequency group were interviewed.
number of hours spent away from their nurslings
suggest that mothers were the princiBoth correlation analysis and nonparapal
That is to say, a mother's percepmetric analysis of variance suggested that
child's developmental progress
several variables from the set of factors idenappears
triggered changes in her
tified in the original research design were
behavior, such that she was more likely to
in fact associated with differences in
breastfeeding behavior among nomadic Tur- be separated from her child for a prolonged
period during the day. Mothers of older nurskana mothers and their nurslings. Clear patlings were observed to spend more time away
terns emerged, which were also consistent
from the herding camp in the performance
with the results of the prospective study
of tasks such as herding and watering ani(Gray, 1994a). Physical status of both mothmals or making purchases in town or in visers and children was associated with varia- iting neighbors. Such activities usually retion in bout frequency in this sample. quired that a woman depart from camp in
Among children, head circumference and the early morning and return after sunset
fatness showed stronger relationships with to avoid travel during the heat of midday,
breastfeeding than did age or any other indi- thus explaining the failure of several women
ces of growth, such as weight or recumbent to breastfeed during this part of the day.
length. The strong relationship between
For nurslings, on the other hand, probout frequency and head circumference is of longed maternal absences were stressful.
particular interest. The most likely explana- The oldest children in the study (older than
tion of this association is that changes in age 18 months) were observed to refuse food
breastfeeding frequency among nomadic during the day, preferring to wait until their
Turkana in the study were not tied as mothers returned. These children were genstrongly to chronological age or size of chil- erally more demanding of the breast when
dren as to behavioral changes which were, their mothers were in camp. In response to
in turn, linked to brain growth and cognitive the persistent nursing demands of older childevelopment. Ifthat was the case, then head dren, their mothers spent longer periods
circumference may be the best anatomical away. Finally, mothers in the sample recorrelate of key developmental milestones ported that the most effective weaning stratrecognized by mothers. Previous studies of egy was to simply leave their child in the
growth of nomadic Turkana children have care of another woman in the awi for several
focussed on weight, height, and fatness, with weeks, while the mother herself went to visit
particular attention to the falling off of friends or relatives.
growth in length and weight during infancy
The relationships between nighttime
(Little et al., 1993)and to patterns of growth bouts and rainfall, wife number, and the
in stature and changes in body composition number of cowives (Table 5) may be related
during childhood and adolescence (Little to another preweaning strategy practiced by
et al., 1984; Little and Johnson, 1987; Little mothers of older children: that of sending
and Gray, 1990). Given the falling-off of nurslings to sleep with another woman in
growth during infancy already established the awi rather than with their mother. The
in this population, it will now be most intri- mother will, on occasion, go to nurse her
guing to examine the pattern of growth in child if it wakes and cries, but it may also
head size, particularly if the latter does in- be fed animal's milk in its mother's absence.
deed trigger changes in care and feeding of Thus, the rainy season, when milk from the
very young children.
herds is more plentiful, is an appropriate
The relationship between breastfeeding time to initiate such a behavioral change. A
bout frequency and age and development of cowife is a logical choice for an alternate
Turkana children raises the question of nighttime caretaker, since an important facagency: did mothers or nurslings actively tor in selecting this strategy, in addition to
initiate changes in infant feeding behavior? the developmental stage of the child, is the
The very strong associations between bout resumption of sexual relations between the
frequency, failure to breastfeed, and the mother and her husband.
Both maternal size and fatness were associated with recalled bout frequency and/or
failure to breastfeed during a part of the day.
The logical explanation of these relationships, at least as they concern fatness or
weight, is that they are simply a reflection of
changes in maternal physical status postpartum: we would expect that mothers of older
nurslings would be thinner. However, the relationships identified here were independent
of the age of nurslings or of any other measures of nursling growth and development. In
other words, after controlling for the age of
their children, smaller and thinner mothers
did in fact breastfeed less frequently.
The peculiar association with maternal
size and body composition may be linked to
relationships between breastfeeding behavior and socioeconomic status. Both sets of
analysis suggested an association between
the depth of the social network and
breastfeeding frequency: the more shallow a
woman’s network was, the fewer the number
of breastfeeding bouts she reported. It is the
case among nomadic Turkana (and among
other groups in the Karimojong cluster) that
wealthier and more resilient herding units
tend to be members of larger networks (Dyson-Hudson, 1966; Johnson, 1990). Conversely, a shallow social network certainly
suggests a less wealthy herding unit. The
absence of any direct correlation between recalled bout frequency and the ranking of the
awi may imply that the social network was
a better indicator of socioeconomic status.
Since large herding units may be split into
satellite units, livestock and human resources of any given awi at the time of the
interview may not have reflected adequately
long-term social and economic stability of
the unit or its true size and composition.
As stated earlier in this paper, the network
is one measure of human resources available, as is the overall wealth of a herding
unit. A shallow network thus has important
implications for the size of the labor pool
of the awi. Gray (1992) demonstrated that
wives of poorer herders spent more time attending to herding duties outside of the
camp, since they had fewer children and cowives who could assist them in such tasks.
Thus, it was expected that poorer women
would spend more hours away from their
infants and hence that they would
breastfeed more infrequently. Table 7 shows
that women in the low-frequency group
spent, on average, 10.1 h out of 24 away from
their nurslings; that was 3.5 h and 5.5 h
more than women in the median- and highfrequency groups, respectively.
The thinness of mothers, coupled with the
thinness of their nurslings, may be an index
of socioeconomic status. Thinness may reflect poorer nutritional status in general.
Size is more problematic, but it is possible
that small size of a Turkana woman equates
in some way with either lower socioeconomic
status of her father’s awi or with lower fertility; if so, smaller, thinner women may be
less desirable marriage partners for wealthy
men and hence may be more likely to be
married to poor herders. This hypothesis
cannot be addressed in the present study, but
it is certainly of interest for future research.
Although of only slight significance, differences between the three groups of women in
rainfall during the month of the interview
were intriguing, since they ran counter to
what might be expected if the onset of the dry
season increased labor demands on mothers
andlor put them at risk of negative energy
balance. If that were indeed the case,
lower rainfall should have been associated
with longer maternal absences and lower
breastfeeding frequency. Instead, rainfall
appears to have been lowest in the months in
which mothers in the high-frequency group
were interviewed. A possible explanation is
that enhanced milk production of the herds
during periods of higher rainfall increased
availability of foods, other than breastmilk,
that were considered appropriate for infants.
Under such conditions, a mother may have
felt less constrained by the nursing demands
of her child and may have spent more time
away from camp, leaving her nursling with
an alternate caretaker and a plentiful supply
of animal’s milk (children are in fact introduced to goat’s and camel’s milk by age 4
months). Again, such behavior may have
been more characteristic of women from
camps of low socioeconomic status, in which
mothers contributed significantly in the
herding of livestock.
The weakness ofthe associations identified
here may be an artifact of the data them-
selves; as discussed earlier, the problems of
recalled breastfeeding data are legion. However, the results of this particular retrospective study are encouraging in that, unlike
other studies based on maternal recall, they
are in agreement with the findings ofthe prospective study (Gray, 1992, 1994a), particularly in relation to the overall frequency of
breastfeeding and changes in nursing behavior among older children. In fact, the
breastfeeding data appear to be more precise
and more reliable than was the case for some
independent variables used in the study: the
difficulty in determining the socioeconomic
rankingoftheawiis acaseinpoint. Nonetheless, the retrospective data were useful in
teasing out relationships suggested by the
much smaller set of prospective data. That
one of the strongest associations identified
was between breastfeeding activity and head
circumference,which may be the best indicator of the progress ofinfant growth and development in this population, increases the credibility of the results.
With regard to the larger study of reproductive ecology of nomadic Turkana of which
the breastfeeding study was but one part,
the long intervals Turkana mothers spent
away from their infants during the day may
have important implications for the timing
of the return to menses postpartum in this
population. It was not unusual, on the one
hand, for mothers of children as young as
8-10 months t o spend five or more hours at
a time away from their children during the
daytime. On the other hand, Turkana infants slept a t their mother’s breast until well
into their second year and nursed on demand
throughout the night. Thus, in this population, suckling patterns during the daytime
hours should prove to have a far more important effect on the duration of lactational
amenorrhea and the timing of the next conception than do nighttime patterns (cf.Jones
1988, 1990). It might also be hypothesized
that duration of amenorrhea is curtailed
among nomadic Turkana, relative to other
natural fertility populations practicing socalled on-demand breastfeeding, since
marked increases in the length of intervals
between breastfeeding bouts were evident
by the time infants reached 10 months (see
also Gray, 1994a).
Of the variables hypothesized to influence
breastfeeding structure among nomadic Turkana, nursling development, maternal size
and fatness, and the depth the maternal social network were most strongly linked to
variation in bout frequency in this sample.
All of these effects appear to have been mediated by the number of hours mothers spent
away from their children over the course of
24 h, behavior which itself was determined
largely by labor demands of the pastoral system. When considered in concert with the
results of the prospective study, the results
of the retrospective component substantially
increase our understanding not only of the
structure of breastfeeding in this population
but also of the ecological factors which introduce variation into that structure and of
their influence on fertility through their effects on breastfeeding structure.
Furthermore, the type of recall data employed here suggests a method of increasing
the precision and reliability of such data
which should be more carefully developed in
future research. As Vitzthum (199413) has
noted, collection of prospective data is timeconsuming and often invasive, and researchers must find more efficient methods of collecting recall data. It is clear from the results
of the Turkana study that future research
may be enhanced by using both methods.
However, the present study should be seen
only as a relatively raw effort; in the future,
it is hoped that refinement of data collection
methods employed here will increase the
range of analytic options available, resulting
in stronger associations between breastfeeding behavior and the full array of biological,
socioeconomic, and behavioral variables
which influence it. At present we have at best
faint hints; it is hoped, in the future, that we
will have a clearly delineated and more precisely modeled biobehavioral phenomenon.
Members of the Turkana households with
whom I worked were extraordinarily cooperative and hospitable, and I am much in their
debt. Turkana women in particular accepted
my presence most graciously and my questions with great patience and humor. Many
_ *
to Ravi Duggirala for his assistance in the
This research was funded by NSF
grant BNS-8718477.
Bernstein IH, Garbin CP, and Teng GK (1988) Applied
Multivariate Analysis. New York: Springer-Verlag
New York Inc.
Bongaarts J (1981) The impact on fertility of traditional
and changing child-spacing practices. In H J Page and
R Lesthaeghe (eds): Child-Spacing in Tropical Africa.
London: Academic Press, pp. 11-129.
Brainard JM (1981) Herders to farmers: The effects of
settlement on the demography of the Turkana population of Kenya. Ph.D. Dissertation, State University of
New York, Binghamton.
Campbell KL, and Wood JW (1988) Fertility in traditional societies. In P Diggory, M Potts, and S %per
(eds.): Natural Human Fertility: Social and Biological
Determinants. Houndmills, Basingstoke: MacMillan
Press, pp. 39-69.
Coughenour MB, Ellis JE, Swift DM, Coppock DL, Galvin K, McCabe JT, and Hart TC (1985) Energy extraction and use in a nomadic pastoral ecosystem. Science 230.519-625.
Dyson-Hudson N (1966) Karimojong Politics. Oxford:
Clarendon Press.
Dyson-Hudson R (1989) Ecological influences on systems of food production and social organization of
South Turkana pastoralists. In V Standen and RA
Foley (eds): Comparative Socioecology: The Behavioral Ecology ofHumans and Other Mammals. Oxford:
Blackwell Scientific Publications, pp. 165-193.
Dyson-Hudson R, and McCabe J T (1985) South Turkana
Nomadism: Coping with an Unpredictably Varying
Environment. HRAFLEX Books Ethnography Series.
New Haven: Human Relations Area Files, Inc.
Ellis JE, and Swift DM (1988) Stability ofAfrican pastoral ecosystems:Alternate paradigms and implications
for development. J . Range Management 4:450-459.
Galvin K (1985) Food Procurement, Diet, Activities and
Nutrition of Ngisonyoka, Turkana Pastoralists in an
Ecological and Social Context. Ph.D. dissertation,
State University of New York, Binghamton.
Gray SJ (1992) Infant Care and Feeding Practices
among Nomadic Turkana Pastoralists of Northwest
Kenya: Implications for Fertility and for Child Survival. Ph.D. dissertation, State University of New
York, Binghamton.
Gray SJ (1994a) Comparison of the effects of breastfeeding practices on birth spacing in three societies: Nomadic Turkana, Gainj and Quechua. J . Biosoc. Sci.
Gray SJ (199413)Correlates of dietary intake of lactating
women in South Turkana. Am. J . Hum. Biol.
Jones RE (1988) Return-to menses postpartum in rural
Indonesian women. Hum. Biol. 60:853.
Jones RE (1990) The effect of initiation of child supplementation on resumption of postpartum menstruation. J . Biosoc. Sci. 22:173-189.
Lamphear J (1992) The Scattering Time: Turkana Responses to Colonial Rule. Oxford: Clarendon Press.
Leslie PW, and Fry PH (1989) Extreme seasonality of
births among nomadic Turkana Pastoralists. Am. J.
Phys. Anthropol. 79:103.
Leslie PW, Fry PH, Galvin K, and McCabe J T (1988)
Biological, behavioral and ecological influences on fertility in Turkana. In EE Whitehead, CF Hutchinson,
BN Timmerman and RG Varady (eds): Arid Lands
Today and Tomorrow: Proceedings of an International
Research and Development Conference. Boulder:
Westview Press, pp. 705-712.
Leslie PW, Campbell KA, and Little MA (1993) Pregnancy loss in nomadic and settled women in Turkana,
Kenya: A prospective study. Hum. Biol. 65:237-254.
Little MA (in press) Adaptability ofAfrican pastoralists.
In SF Ulijaszek and R Huss-Ashmore (eds): Human
Adaptability: Past, Present and Future.
Little MA, and Gray SJ (1990) Growth of young nomadic
and settled Turkana children. Med. Anthropol. Q.
Little MA, and Johnson BR (1987) Mixed-longitudinal
growth of nomadic Turkana pastoralists. Hum. Biol.
Little MA, Galvin K, and Mugambi M (1984) Crosssectional growth of nomadic Turkana pastoralists.
Hum. Biol. 55:811-830.
Little MA, Galvin K, and Leslie PW (1988) Human
growth, health and energy requirements in nomadic
Turkana pastoralists. In I deGarine and GA Harrison
(eds): Coping with Uncertainty in Food Supply. Oxford: Oxford University Press, pp. 288-315.
Little MA, Gray SJ, and Leslie PW (1993) Growth of
nomadic and settled Turkana infants of northwest Kenya. Am. J . Phys. Anthropol. 92:273-289.
McNeilly AS, Glasier A, and Howie PW (1985)Endocrine
control of lactational infertility. In J Dobbing (ed):
Maternal Nutrition and Lactational Infertility. New
York Raven Press, pp. 1-24.
McNeilly AS, Howie PW, and Glasier A (1988) Lactation
and the return of ovulation. In P Diggory, M Potts,
and S Teper (eds.): Natural Human Fertility: Social
and Biological Determinants, Houndmills, Basingstoke: MacMillan Press, pp. 102-117.
Mugambi M, and Little MA (1983) Blood pressure in
nomadic Turkana pastoralists. East Afr. Med. J.
Panter-Brick C (1991) Lactation, birth spacing and maternal workloads among two castes in rural Nepal. J .
Biosoc. Sci. 23:137-154.
Popkin BM, Laskey T, Litvin J , Spicer D, and Yamamoto
ME (1986) The Infant Feeding Triad. New York: Gordon and Breach Science Publishers.
Sokal RR, and Rohlf FJ (1981) Biometry, 2nd ed. New
York: W.H. Freeman and Co.
Vitzthum VJ (1988)Variation in infant feeding practices
in an Andean community. Michigan Studies in Andean
Anthropology, Michigan Discussions in Anthropology 8:137-156.
Vitzthum VJ (1989) Nursing behavior and its relation
to duration of postpartum amenorrhea in an Andean
community. J . Biosoc. Sci. 21:145-160.
Vitzthum VJ (1994a) Comparative study of breastfeeding structure and its relation to human reproductive
ecology. Yrbk. Phys. Anthropol. 37307-349.
Vitzthum VJ (1994b) Suckling patterns: Lack of concordance between maternal recall and observational
data. Am J. Hum. Biol. 6:551-562.
Vossen R (1982) The Eastern Nilotes: Linguistic and
Historical Reconstructions. Berlin: Deitrich Reimer
Wienpahl J (1984) The Role of Women and Small Stock
Among the Turkana. Ph.D. dissertation, University of
Arizona, Tucson.
Lai D, Johnson PL, Campbell KL, and Maslar
Wood JW,
IA (1985)Lactation and birth spacing in highland New
Guinea. J . Biosoc. Sci. Suppl. 9:159.
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