growth patterns among seminomadic pastoralists (datoga) of tanzania

Growth Patterns Among Seminomadic Pastoralists(Datoga) of Tanzania

DANIEL W. SELLEN*Department of Anthropology, Emory University, Atlanta, Georgia 30322

KEY WORDS Africa; herders; children; anthropometry; delayedmaturation; catch-up growth; stunting; wasting; undernutrition;nutrition

ABSTRACT Anthropometric measurements made on 470 individual chil-dren (age 0–18 years) from a seminomadic population of Datoga pastoralistsliving in northern Tanzania were used to describe patterns of child growth.Comparisons with reference growth curves derived from American samplessuggest that pastoral Datoga children grow poorly in this region. Bodycompositional changes with age differed markedly from the reference popula-tion. There were negligible fat gains through childhood, even among females.Comparison with data on other East African pastoralists showed thatpopulation growth performance is intermediate between that of nomadic andsettled pastoralists. Little catch-up growth occurs during childhood, andadolescence appears to be delayed among males. The results contribute to thegrowing database on health indicators for African pastoralists and suggest aneed for further research to investigate mechanisms for growth stunting inthese populations.Am J PhysAnthropol 109:187–209, 1999. r 1999 Wiley-Liss, Inc.

Clinicians and anthropologists have longbeen interested in how environment influ-ences patterns of child growth, but associa-tions with subsistence practices remainpoorly investigated. It has been hypoth-esized that much of the variation in bodysize among rural African populations maybe attributable to differences in dietary ad-equacy, energy requirements, and infectionrates among populations engaged in differ-ent subsistence practices (Wheeler, 1980).While there have been a number of recentsurveys of nutritional status and food sup-ply in sub-Saharan African pastoral popula-tions (Benefice et al., 1984; Loutan andLamotte, 1984; Loutan, 1985; Brainard,1986, 1990; Nestel and Geissler, 1986; Ber-nus, 1988; Nestel, 1989; White, 1991; Gal-vin, 1992; Lindtjørn et al., 1992, 1993; Littleet al., 1992; Hansen et al., 1993; Galvin etal., 1994; Gray, 1994; Shell-Duncan, 1995;Nathan et al., 1996), relatively few pub-lished studies have estimated patterns of

child growth (Little et al., 1983, 1993; Dowleret al., 1986; Little and Johnson, 1987; Littleand Gray, 1990b; Cameron, 1991; Sellen,1996; Little, 1998).

The Eyasi Datoga are seminomadic pasto-ralists who keep cattle, sheep, and goats formilk, meat, and trade for grain (Klima,1965; Borgerhoff Mulder, 1991; Sellen, 1995).This paper examines data from cross-sec-tional surveys of child anthropometry amongthe Eyasi Datoga living at three settlementareas. Objectives were to examine the distri-butions of anthropometric scores of childrenin relation to seasonality, settlement area,home environment, age-related work activi-ties, and sex-biased parental investment

Grant sponsor: Wenner-Gren Foundation for AnthropologicalResearch; Grant sponsor: Royal Anthropological Institute ofGreat Britain; Grant sponsor: Leverhulme Trust.

*Correspondence to: Daniel W. Sellen, Department of Anthro-pology, Emory University, 1557 Pierce Dr., NE, Atlanta, GA30322. E-mail: [email protected]

Received 29 April 1998; accepted 7 March 1999.

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 109:187–209 (1999)

r 1999 WILEY-LISS, INC.

strategies, to establish the prevalence ofindicators of undernutrition in the popula-tion, and to examine patterns of growth.Here we assess the overall growth pattern ofthe population by constructing mixed-longi-tudinal growth curves and comparing theseto appropriate growth reference data.

MATERIALS AND METHODSSubjects

The Datoga are Kalenjin-speaking pasto-ralists known to have occupied large areas ofTanzania and southern Kenya for much ofthe last millennium (Borgerhoff Mulder etal., 1989; Sellen, 1995). They have a recenthistory of territorial losses due to wars withthe Maasai and Sukuma, aggressive Ger-man and British colonial policies, and postin-dependence encroachment by agriculturistsand government projects (Kjaerby andBaynit, 1979; Lane and Pretty, 1990). Theirpresent range is restricted to some of themore arid and least accessible areas of northand central Tanzania. Previous anthropologi-cal research focused on the Barabaig clansubsection that inhabits the relatively wet

areas surrounding Mount Hanang (Klima,1965; Blystad, 1992).

A cross-sectional survey approach wasused to sample Datoga children living in theLake Eyasi basin (Fig. 1). The Eyasi Datogadefine themselves as people who herd cattleand subsist on herds of cattle, sheep, andgoats, and all families had herds. Partici-pant observation and household food sur-veys confirmed that few bush foods wereconsumed, and dietary studies showed thatmost calories consumed are derived fromgrain obtained through trade (Sellen et al.,1993). No adequate census data exist for theDatoga, and population estimates vary sub-stantially from 30,000–200,000 (BorgerhoffMulder, 1992). They are ‘‘seminomadic’’(Umesao, 1968; Tomikawa, 1979), and havelargely avoided economic, social, and politi-cal involvement in the state. It is not clearwhether this is a cause or an effect of theirpoor political representation and strong dis-crimination within present-day Tanzania.Despite the availability of primary schoolsat villages in the area, few children are sentto school. Few men (approximately 60%) and

Fig. 1. Map showing location of the Eyasi area.

188 D.W. SELLEN

fewer women (30%) can speak KiSwahili,the official language and regional linguafranca. Illiteracy is almost universal.

Families base their activities at semiper-manent family homesteads ( ghed). Eachghed consists of a cluster of timber and earthhuts, sheds for goats and calves, maizestores, and compounds for the larger live-stock, all enclosed within a thorn brushstockade for protection against predatorsand human raiders. One or more (usuallyagnatically related) men, some or all of theirwives and children, a few collateral kin, anda variable number of livestock occupy home-steads. All household members participatein herding tasks. Women collect water andfuel wood by hand. The diet consists of maizepurchased from neighboring agriculturalpopulations and animal products, supple-mented by a few wild foods.

Demographic parameters for the Datogapopulation in the Eyasi area have beenestimated for a sample that includes house-holds from the present study (BorgerhoffMulder, 1992). No modern forms of contra-ception are used, and total fertility is high inrelation to other pastoral groups (Lane andPretty, 1990; Roth, 1994). However, birthintervals are long, reflecting the interplaybetween prolonged breast-feeding practices(Sellen, 1998b), work outputs (Sieff, n.d.)and seasonal factors (Borgerhoff Mulder,1992). Infant mortality approaches 20% andis high by national and international stan-dards; mortality remains relatively highthroughout life. The major causes of mortal-ity are not well-investigated to date, buthave been observed to include tetanus of thenewborn, and dehydration and respiratorytract infections among young children. Ma-laria, diarrhea, gut parasites, and tuberculo-sis are prevalent among adults; the illnessesmost commonly treated by local flying doc-tors are scabies, eye infections, and infected

leg injuries sustained while walking in thebush. The diseases of cattle are many, andinclude several transmissible to humans:brucellosis, tuberculosis, tick-borne dis-eases, and anthrax. Physicians at one hospi-tal near the study site reported in 1989 thatseveral Datoga patients had presented withsymptoms of AIDS or tested HIV-positive.

Data collected in both cross-sectional andlongitudinal studies were used to describegrowth patterns for children in the popula-tion. A census and a round of anthropomet-ric measurements were carried out for chil-dren of all ages during two cross-sectionalsurveys between April–June 1989 and Janu-ary–March 1991. These surveys were de-signed to achieve maximum coverage ofhouseholds in the area and were 80% suc-cessful (Sellen, 1995). A total of 444 childrenwas measured (Table 1). In 27 cases, mainlyolder adolescents, the age estimate obtainedfrom informants at the time of measurementwas deemed unreliable and therefore theirmeasurement series were excluded fromanalysis. Among the series retained foranalysis there was an overlap of 28 subjectsmeasured in both surveys. Thus, a total of389 subjects measured in at least one of thesurveys was included in this analysis. An-thropometric measures were also takenmonthly between the end of the long rains(May) and the beginning of the short rains(December) of 1992 for 78 children underage 3 years living in two Datoga settlementsas part of a prospective study of growth andfeeding practices (Sellen, 1998b).

Anthropometric measures used

Since the target population lives scatteredover a wide area, and individual womenhave little time available to walk or bringtheir children to central meeting points,each of the homesteads was visited in turnand the measurement equipment set up

TABLE 1. Summary of cross-sectional anthropometric samples1

Initial sample andexclusions Survey 1 Survey 2 Totals

Total number of children on which measurementswere made 286 [121, 165] 158 [74, 84] 444 [195, 249]

Age not satisfactorily determined from informants 6 [3, 3] 21 [11, 10] 27 [14, 13]Final sample size, 0–18 years 270 [116, 154] 131 [62, 69] 417 [181, 236]1 In brackets: males and females, respectively.

189GROWTH OF AFRICAN PASTORALISTS

within the compound or under a nearbyshade tree. On any single visit, not allsubjects would be home, and often repeatvisits were necessary at different times ofday, so as to include as many women andchildren of herding age as possible. Thesame observer (D.W.S.) made every measure-ment following standard procedures (Jelliffeand Jelliffe, 1989; Frisancho, 1990; Gibson,1990). Barefoot standing height was mea-sured to the nearest millimeter using aportable anthropometer (Model 101, Seri-tex, Inc., East Rutherford, NJ), attached to aflat metal platform which was dug level intothe ground using a hoe and a spirit-level.Subjects were encouraged to stand tall withheads level, and the chin-support methodwas used to raise the younger children to thecorrect height. Any child that could standwas encouraged to be measured, and chil-dren as small as 75 cm (and as young as 12months) were successfully measured in this

way. The need to carry all equipment on footprecluded the use of a board in the surveys,so that measures of recumbent length orstature were not taken for infants and chil-dren under 24 months (n 5 56, survey 1; n 533, survey 2). However, recumbent lengthwas measured for all 81 children in thelongitudinal study.

Weights of children were measured to thenearest 0.1 kg using a digital scales (survey1, 12-v battery-operated Weylux Model 850;survey 2, AA battery-operated SoehlnerModel 7701; both from CMS Weighing Ltd.,London, UK). If young children were veryfussy or sick, they would be weighed bydifference with the mother or caregiverstanding on the digital scales with andwithout the young child. Infants wereweighed directly with a spring balance tothe nearest 0.2 kg (Salter Industrial Mea-surement Ltd., West Bromwich, West Mid-lands, UK). Naked weight was measured for

Fig. 2.

190 D.W. SELLEN

all younger children. For older children,shoes were removed but clothing and jew-elry were worn at the time of weighing andeach item was tallied. Most clothing itemswere of a limited number of types of clothwrap (akin to a Roman toga) which aretraditionally sold and used in the area(KiSwahili: mashuka, vikoi) and are distin-guishable by material, color, and size. There-fore, the mean weight of a random sample ofeach type was calculated. These mean val-ues were then used to make standard sub-tractions from the gross weights of individu-als who wore particular garments atmeasurement, and the resulting estimatedunclothed weights were used in analysis.The midpoint of the brachium was locatedby measurement from the acromion of theshoulder to the olecranon process of theelbow, and the circumference at that point

measured to the nearest millimeter using asmall steel tape (Rabone Chesterman Ltd.,Birmingham, UK). All arm measurementswere taken on the right side so as to maxi-mize comparability to North American refer-ence data (Martorell et al., 1988). Two skinfolds were measured in each subject to thenearest 0.2 mm with a Harpenden skin-foldcaliper (Hemco Corporation, Holland, MI),taking the average of three separate read-ings. Triceps skin-fold thickness (TSF) wasmeasured at the previously marked mid-point of the right upper arm (except wherenoted above), and subscapular skin-foldthickness (SSF) was measured at the infe-rior angle of the right scapula.

No birth records exist for the population.Year and month of birth of children weretherefore obtained through interviews withparents or other family members (USAID,

Fig. 2. Average weight gains of young Datoga children plotted against multiethnic American referencedata (Department of Health, Education, and Welfare, 1977b): mixed-longitudinal data, 190 measures on78 children, means 6 SD. a: Girls. b: Boys.


1979). A standard cross-checking methodol-ogy developed by small population demogra-phers was applied (Howell, 1979; Cronk,1989; Leslie and Gage, 1989; Blurton Joneset al., 1992; Borgerhoff Mulder, 1992; Pen-nington and Harpending, 1993; Hill andHurtado, 1996). Informants were asked toplace the date of birth of each child on a localcalendar of events developed by previousresearchers and updated by the presentauthor (Sellen et al., 1993). The date of birthwas arrived at to the nearest month byconsensus in almost all instances. Infor-mants apparently had little difficulty nam-ing and agreeing upon dates for childrenunder 5 years, although there was moredifficulty in recalling, and more debate over,the dates of birth of children in their teens.Secondary sexual characteristics were notsystematically observed in adolescents be-cause of the constraints of the conditions ofmeasurement (out in the open) and difficultyin recruiting female research assistants.

Data for height, weight, age, and sex wereused to compare all individual children tothe appropriate CDC/NCHS/WHO interna-tional reference based on multiethnic USsamples collected by the Fels Research Insti-tute and the National Center for HealthStatistics (Department of Health, Educa-tion, and Welfare, 1977a,b). Upper armmuscle area (UMA without adjustment forestimated bone area) and arm fat index(AFI: the percentage of fat in the upper arm)were estimated from the measures of upperarm circumference (MUAC) and triceps skinfold (TSF) according to the method of Frisan-cho (1990, p.20). The distribution of each ofthese measures of body composition by ageand sex was then compared to that esti-mated forAfricanAmericans in the NHANESI and NHANES II surveys conducted by theUS National Center for Health Statistics(Frisancho, 1990). Statistical analyses wereperformed using the SAS package (SAS Insti-tute, 1989) on a personal computer. Paired

Fig. 3.

192 D.W. SELLEN

and unpaired t-tests, x2 tests, and analysesof variance were performed at the 5% level ofsignificance.

RESULTSMixed-longitudinal estimates of growth in

young children

Early growth faltering was examined us-ing the measures of weight and head circum-ference made on 78 individuals included inthe longitudinal study of children under 3years of age. The mixed cross-sectionalgrowth patterns observed in this samplewere compared to the cross-sectional pat-terns observed in the multiethnic NCHS/CDC/WHO reference population (Figs. 2, 3).Growth faltering of infants was clear afterage 3 months for girls and age 6 months forboys. The mean weights for age fell to the5th percentile by 9 months of age and belowthe 5th percentile after 18 months (Fig. 2).Lengths for age were also below reference

medians at all ages 0–3 years. Mean headcircumference remained close to the refer-ence median until 9 months for girls and 12months for boys, after which it fell at orbelow the 5th percentiles (Fig. 3).

Comparison of growth in weight andstature with US reference data

To facilitate comparison with other pasto-ral populations for which growth data arecommonly presented using 1-year intervals,Table 2 shows the mean anthropometricvalues for girls and boys measured in bothcross-sectional surveys grouped by age tothe nearest year, including repeated mea-sures on 28 children. Means were found tofall below the medians of the NCHS refer-ence curves at all ages. To provide a morerefined visual description given the con-straints of the small sample and to examinechanges in sampling error with age, mixed-longitudinal growth curves were constructed

Fig. 3. Average head circumference of young Datoga children plotted against multiethnic Americanreference data (Department of Health, Education, and Welfare, 1977b): mixed-longitudinal data, 190measures on 78 children, means 6 SD. a: Girls. b: Boys.


after pooling data from both surveys. Meansand standard deviations of weights andheights of boys and girls were calculated at6-month intervals for children younger than12 years and at annual intervals for children12–18 years (Figs. 4, 5). Estimates based onsample sizes less than three were not plot-ted.

Mean weights of girls were found to fall alittle above the 5th percentile of standardsuntil about the ninth year, after which therewas a drop in weights for age, and a markedincrease in the variance between individu-als, which remained through the teenage

years (Fig. 4a). The data suggest that themean weight of adult women in this popula-tion (approximately 47 kg) is achieved by 18years of age (Table 2), which is also themedian age at marriage. In contrast, meanweights of boys were found a little below the5th percentile of standards until about theninth year, after which mean weights for agefell increasingly below the 5th percentile. At16 years the mean weight was but 60% ofthe standard median (Fig. 4b).

Mean heights of girls were found to fallabove the 5th percentile until the ninth year(Fig. 5a). Between 5–9 years they fell around

TABLE 2. Means and standard deviations of anthropometric measures taken on a cross section of childrenfrom a seminomadic Datoga population1

Age(years) N

HT TRUWT WHI TRISF SUBSF SUMSF MUAC

Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD

Females

,1 21 * * 6.8 2.0 * * 7.9 2.2 5.9 2.0 13.7 3.8 12.9 0.81–1.99 19 76.9 5.2 8.4 1.4 16.1 2.4 8.5 1.8 5.6 2.0 14.0 2.5 14.0 1.12–2.99 17 89.5 7.0 11.2 1.9 14.6 2.1 9.2 2.1 5.1 1.0 14.3 2.4 14.6 1.03–3.99 20 94.6 9.9 13.1 2.4 14.6 1.2 7.4 2.2 4.8 1.1 12.2 2.5 14.4 0.84–4.99 19 97.5 8.6 13.8 2.3 14.6 1.4 7.4 1.7 4.7 1.2 12.2 2.6 14.5 0.95–5.99 24 107.6 9.7 15.9 3.2 13.8 1.0 5.9 1.7 4.5 1.2 10.4 2.4 14.8 1.16–6.99 10 111.5 8.1 16.8 3.2 13.4 1.1 6.0 2.5 4.1 0.6 10.1 3.0 14.9 1.37–7.99 14 120.2 6.2 19.9 2.4 13.8 1.0 4.7 1.3 4.0 0.7 8.7 1.9 15.4 1.18–8.99 6 125.7 5.1 22.1 1.3 14.0 0.6 5.7 1.4 4.7 0.7 10.3 1.6 16.3 0.89–9.99 16 125.1 8.2 21.5 3.9 13.6 1.3 5.9 1.3 5.0 0.8 10.8 1.7 15.7 1.3

10–10.99 12 131.9 10.2 23.7 4.2 13.3 1.3 5.3 1.6 4.9 1.3 10.2 2.4 16.2 1.511–11.99 12 135.1 7.0 27.0 4.2 14.7 1.5 6.0 1.7 4.8 0.7 10.8 2.1 17.0 1.812–12.99 12 137.4 7.1 28.6 6.6 15.1 2.3 6.9 2.0 6.0 2.7 13.0 4.3 17.9 2.213–13.99 7 149.2 10.6 34.2 6.5 15.7 2.2 7.1 2.9 5.0 1.1 12.1 3.6 18.9 1.214–14.99 10 149.1 6.3 35.5 5.3 16.0 2.4 8.1 3.7 5.6 2.7 13.7 5.1 19.5 1.815–15.99 9 152.4 8.1 38.0 8.2 16.3 2.1 7.9 3.0 4.4 2.3 12.3 2.6 20.7 2.516–16.99 4 156.7 5.8 38.3 7.4 15.5 2.5 5.6 1.9 6.8 2.7 12.5 4.6 20.1 2.917–17.99 2 166.8 5.6 46.2 1.4 16.6 0.6 5.9 0.0 6.7 0.4 12.6 0.4 20.1 0.518–18.99 2 149.3 6.7 41.0 9.2 18.3 2.5 6.9 2.3 6.6 2.1 13.4 4.4 20.0 1.3Total 236

Males

,1 24 * * 6.5 1.7 * * 8.1 2.1 6.2 1.9 14.0 3.5 13.4 1.11–1.99 11 76.8 5.0 9.8 1.1 15.4 0.0 9.2 1.9 5.4 1.7 14.5 3.2 14.2 1.52–2.99 16 84.7 4.7 10.9 1.4 15.6 1.0 9.2 2.5 5.1 1.3 14.3 3.4 13.8 0.83–3.99 22 92.7 6.1 12.8 2.5 15.4 1.5 8.3 2.3 4.9 1.0 13.2 3.1 14.7 1.44–4.99 10 99.1 5.7 15.6 2.6 15.3 0.9 7.5 1.3 4.5 1.1 12.0 1.5 14.7 1.35–5.99 14 104.0 8.9 15.7 2.3 14.5 1.4 7.6 2.7 4.6 0.8 12.3 3.3 14.7 1.16–6.99 12 112.4 5.9 17.6 2.7 13.8 1.3 5.8 2.1 3.9 0.6 9.7 2.6 14.9 1.47–7.99 9 118.2 9.6 20.2 4.0 14.3 1.1 4.8 0.8 4.4 0.6 9.3 1.2 15.0 1.38–8.99 5 124.2 3.9 21.6 1.9 14.0 0.7 5.0 1.2 4.6 0.9 9.6 2.0 14.9 1.09–9.99 12 126.3 2.9 23.2 2.0 14.6 1.0 5.1 0.9 4.6 1.0 9.6 1.7 15.8 1.2

10–10.99 9 132.2 9.4 24.5 3.8 13.9 1.1 4.2 1.0 3.9 0.2 8.1 1.1 15.2 1.011–11.99 10 136.1 5.8 27.6 2.5 14.9 1.3 5.3 0.9 4.5 0.7 9.8 1.6 15.7 2.012–12.99 9 142.6 9.2 29.1 4.3 14.3 0.4 5.1 1.1 5.0 1.8 10.1 1.9 15.8 1.713–13.99 5 139.0 8.7 29.7 5.0 15.3 0.7 5.0 1.5 5.0 1.5 10.0 2.5 18.9 0.914–14.99 8 141.4 9.4 30.1 4.8 15.0 1.0 5.7 1.8 4.8 1.4 10.4 3.2 17.6 2.315–15.99 3 145.4 2.6 35.1 2.7 16.6 0.7 6.0 0.3 4.8 0.6 10.8 0.4 18.9 0.816–16.99 2 159.1 2.8 36.5 5.9 14.4 1.8 3.4 0.9 3.6 0.6 6.9 1.6 17.8 3.3Total 1811 SD, standard deviation of the mean; HT, height (cm); * missing data; WT, weight (Kg); WHI, weight/height2 (Kg/m2); TRISF, tricepsskin fold (mm); SUBSF, subscapular skin fold (mm); SUMSF, sum of triceps and subscapular skin folds (mm); MUAC, mid upper armcircumference (cm).

194 D.W. SELLEN

the 25th percentile. Thereafter they were alittle below the 5th percentile until thesixteenth year. Growth in stature of boysappeared to be more strongly compromised.Mean heights of boys were found to fall nearthe 5th percentile of the reference popula-tion (approximately 90% of reference me-dian) until the tenth year and below it intothe teens (Fig. 5b).

Comparison of growth in weight andstature with Turkana pastoralists

Mean weights and heights by age in yearswere also compared for each sex with thoseavailable from similar studies of both no-madic and settled Turkana pastoralists(Little et al., 1983, 1993; Little and Gray,1990a) and with means for the AfricanAmerican subsample of the US referencepopulation (Figs. 6, 7). This approach waschosen because the slightly differing rates ofheight and weight gain with age amongethnic groups are obscured in the ethnicallymixed NCHS/CDC/WHO sample (Frisan-cho, 1990; Gibson, 1990). Although the Afri-can American curves are similar to theaggregate curves, because there are somedifferences among older children they aretherefore the most appropriate availablereference for the present population. Allthree of these ‘‘pastoral’’ populations fellbelow the US reference means. Datoga girlswere on average a little taller and heavierthan nomadic Turkana girls until 10 years ofage; after 10 years, heights became verysimilar, but Datoga girls tended to be heavierfor age as teenagers. Datoga boys were onaverage taller and heavier for age thannomadic Turkana boys until 13 years of age,after which there appeared to be little consis-tent difference. Datoga children of both sexeswere of similar weights for age as settledTurkana, at least over the age range forwhich data could be compared, but wereappreciably shorter.

Age-related changes in fat reserves

Children of both sexes showed a decreasein measures of adiposity between 2–7 yearsof age (Fig. 8). After 10 years of age, girlsshowed a gradual increase in summed skinfolds, whereas boys showed little change.Mean values of estimated arm fat and muscle

areas of children were found to be smallerthan those from the African American refer-ence population at all ages from 2–18 yearsfor both boys and girls (Fig. 9). Among girls,mean muscle areas, though consistentlylower than standards, showed rates of in-crease with age from 2–9 years similar tothose of standards (Fig. 9a). Upper-arm fatarea of girls increased very little, even in theteenage years, in marked contrast to stan-dards. At 17 years of age, mean areas of bothmuscle and fat were still much lower thanthe means found for adult married women,suggesting that some tissue growth contin-ues after marriage. Muscle areas of boyswere found to increase, on average, at a slowrate relative to standards (Fig. 9b). Boys inthe 8–12-year age range had very similarupper arm muscle areas in this sample,suggesting that perhaps rates of gain in leanbody mass were slowed in late childhood.Most notably, there was little appreciablearm muscle growth between 9–13 years. Bythe late teens, mean muscle areas were lessthan 50% of those in the US reference popu-lation. Mean arm fat areas decreased until 8years of age, as is the pattern in the refer-ence population, but remained very lowthereafter, with little appreciable preadoles-cent or adolescent fat gains.

DISCUSSIONQuality of the growth data

A strong attempt was made to obtain aslarge and representative a sample of childmeasures as possible under the logistic andtechnical constraints encountered in thefield. In spite of these efforts, the study wassubject to several of the potential samplingbiases typical of most published studies ofseminomadic African pastoralists (Sellen,1996). The sample was biased towards girls,and teenagers were almost certainly under-represented. Ages were difficult to ascertainreliably because of the imprecision of agedetermination. Even though birth dates werecollected to the nearest month, there wassome ‘‘heaping’’ of age estimates to the near-est year for teenagers. However, the smallproportion (15 cases) of height-for-age Z-scores (HAZ), greater or less than 2 stan-dard deviations from the mean for the popu-lation measured in each survey suggested


that most age estimates were reasonablyaccurate and not systematically biased foreither sex or any particular developmentalstage.

The results are unlikely to reflect biasestowards certain subsections of the popula-tion, such as poorer or less mobile house-holds. This is because of the relatively largesample sizes, the inclusion of virtually everyhousehold in a defined large area of theEyasi valley system, the careful use of ethno-graphic techniques of age estimation, andthe rigorous exclusion of potentially invalidor unrepresentative data. They are there-fore deemed adequate for drawing validinferences about the growth status of chil-dren within the population.

Early childhood growth faltering

The cross-sectional data from the twosurveys indicated that much of the deficit ingrowth relative to the reference was already

established by the second year of age. Themixed-longitudinal study of infants andweanlings in the Eyasi Datoga shows thatgrowth deficits occur in the first 3–6 monthsof life and occur earlier for girls (Fig. 2).There are likely to be a number of contribut-ing causes. First, adult women are of poornutritional status and are likely to givebirth to babies of low birth weight (Sellen,1995). Unfortunately, since only a smallproportion of Datoga infants are weighed atbirth in a clinic setting, no data on birthweights are available and this hypothesiscannot be directly tested. Second, earlygrowth faltering is likely to be linked withinadequate food intake. A proportion ofhouseholds are estimated to have inad-equate food supplies (Sellen, 1995). TheDatoga diet consists largely of maize gruelor stiff porridge, which is a low nutrientdensity food, only infrequently supplementedwith animal milks, leafy vegetables, and

Fig. 4.

196 D.W. SELLEN

meat. Observations of infant and youngchild feeding practices suggest that youngerchildren are buffered from the seasonal fluc-tuations in household food supply by contin-ued breast-feeding of long duration and bythe mother’s relinquishing her intrahouse-hold food allocations to her offspring. Al-though children’s nutritional status does notappear to be related to seasonal factors thatmight influence food availability, young childdiets remain inadequate in key respects(Sellen, 1998b). In comparison to standardweaning recommendations, children aresupplemented with animal milks at a rela-tively young age (median 2 months) andcomplemented with solid foods at a rela-tively late age (median 11 months in thecase of introduction of maize porridge). Thus,despite an almost universal initiation of

breast-feeding, exclusive breast-feeding israre and of short duration, while the grueland porridge commonly used as the princi-pal weaning foods are unlikely to satisfy thenutrient needs of weanlings. Young childfeeding practices are likely to have negativeeffects on growth.

Third, early growth faltering is likely to belinked with high rates of infection (Moy etal., 1994; Shell-Duncan, 1995; Nathan et al.,1996). Datoga children under 5 years showhigh mortality (Borgerhoff Mulder, 1992).The importance of young child morbidity inreducing young child food intakes and modi-fying maternal feeding practices was as-sessed in the longitudinal study of childrenunder 3 years from caregiver reports of thesubject child’s illnesses during the 24 hrprior to each visit. The symptoms were

Fig. 4. Age distribution of mean weights of Datoga children, 0–18 years, plotted against multiethnicAmerican reference data. Solid lines show mixed-longitudinal growth curves of Datoga children 6 1 SD.Dotted lines show 50th and 5th percentiles of the NCHS reference data (Hamill et al., 1979). a: Meanweights of Datoga girls, n 5 217 child measures, 0–16 years. b: Mean weights of Datoga boys, n 5 173child measures, 0–16 years.


described by the caregiver without leadingquestions from the interviewer. Symptomsof nondiarrhea illnesses affected childrenyounger than 3 years on over 40% of days,and usually occurred simultaneously withsymptoms of diarrhea (Table 3). Amongthese, symptoms of febrile diseases, princi-pally malaria, and respiratory infectionswere most prevalent. The most commonsymptom of illness was diarrhea, whichaffected children in this sample on almost 1out of 3 days. These patterns of illnessamong young children suggest that growthmay be compromised by frequent and ex-tended periods of fever and anorexia.

We have evidence that social factors alsostrongly influence the autecology of youngchild growth among the Datoga, not simplyby affecting food availability, food intakes,and susceptibility to infection, but by subtlyaffecting components of young child careand feeding behaviors. For example, mater-

nal work-related factors interfere with theability of mothers to frequently breast-feedtheir young children and result in earlyintroduction of contaminated liquid foods,reduced breast-milk intakes, and early ces-sation of breast-feeding (Sellen, 1998b). Thegrowth of young children is associated withthe different positions within polygynousmarriages occupied by their mothers (Sellen,1995, 1999). There is also indirect evidencethat both early and later child growth perfor-mance is associated with complex co-wifeeffects which derive from differential mater-nal workloads, such that senior wives do lessdemanding or time-consuming work, or con-trol more material resources within house-holds (Sellen et al., 1999). Finally, it ishighly likely that differences in workloadsamong women in households of different sizeand composition may also play a role. Womenin households with more adult laborers andfewer dependent children may do less de-

Fig. 5.

198 D.W. SELLEN

manding or time-consuming work (Sieff,1997).

Lack of catch-up growth and adolescentgrowth ‘‘faltering’’

Although mixed-longitudinal growthcurves do not necessarily reflect the growthtrajectories of individuals, we can infer thatthe average child follows an initial growthtrajectory that places her at around the 5thpercentile of the appropriate referenceweights and heights by 2–3 years of age.Rates of growth then appear to be similar tothose in the reference population until about10 years of age. Consequently, most childrennever overcome the initial deficits acquiredin early childhood. Anthropometric deficitsare even greater after about 10 years of age(before which most Western populations

show a prepubertal velocity slow-down) andgreatest after 12–14 years (the median agerange for puberty in girls and boys in thereference populations). The increased meandeficits among teens in all measures of bodysize relative to the international referencecoincide with increased variance in statureamong teenagers. Such a pattern is typicallyobserved in cross-sectional and mixed-longi-tudinal data such as those given here and isbest interpreted as due to the growth spurtin individuals coming at different ages ratherthan reflecting increased sampling errorsassociated with smaller sample sizes.

These observations generate several im-portant questions. First, why do survivingchildren in this population fail to catch upwith reference medians even by the lateteens? Second, given that childhood growth

Fig. 5. Age distribution of mean heights of Datoga children, 1–18 years, plotted against multiethnicAmerican reference data. Solid lines show mixed-longitudinal growth curves of Datoga children 6 1 SD.Dotted lines show 50th and 5th percentiles of the NCHS reference data (Hamill et al., 1979). a: Meanheights of Datoga girls, n 5 200 child measures, 1–16 years. b: Mean heights of Datoga boys, n 5 154 childmeasures, 1–16 years.


retardation has been recorded among sev-eral populations of African pastoralists andagropastoralists, how is it that adult statureoften falls within the median range of refer-ences? Third, are the increased deficits ob-served among teenagers in all measures ofbody size relative to the reference popula-tion the result of delayed maturation, acohort effect, or increased environmentalinsults in this age range? Fourth, how canwe account for the observed variation inmixed-longitudinal growth patterns amongpopulations of African pastoralists?

There is debate in the literature as towhether complete catch-up growth (Praderet al., 1963; Eveleth and Tanner, 1990, p.192) is physiologically possible in childrenwho suffer growth retardation at a youngage (Beaton, 1992; Dewey et al., 1996;Golden, 1996). Some observers have con-cluded that there is little evidence of catch-upgrowth in later childhood and adolescence(Martorell et al., 1979, 1994; Karlberg et al.,1988; Pelletier et al., 1991). They point out

that growth rates appear fairly uniformduring middle childhood and adolescenceacross a variety of settings, so that an earlyperiod of growth faltering is followed by, atbest, an otherwise normal growth trajectory,rather than an adaptively accelerated growthtrajectory. The implication is that humangrowth potential is ‘‘locked in’’ at an earlyage (Martorell et al., 1992; Karlberg et al.,1994). Certainly, the cross-sectional growthtrajectories reported here suggest thatamong the Datoga population as a whole,appreciable catch-up does not occur in middlechildhood or in the age range correspondingto adolescence in the reference population.

A number of studies have described appar-ently spontaneous catch-up without inter-vention in several populations of stuntedchildren (Alvear et al., 1886; Driezen et al.,1967; Keet et al., 1971; Graham and Adrian-zen, 1972; Satyanarayana et al., 1981, 1996;Graham et al., 1982; Kulin et al., 1982;Little et al., 1983). We must infer that theinsults suffered by the children in these

Fig. 6.

200 D.W. SELLEN

studies may have been qualitatively differ-ent from those suffered by Datoga childrenand other stunted populations in which afailure to catch up was reported (Golden,1996). Other studies have demonstratedcatch-up growth among stunted childrenmoved to conditions of better nutrition andlower disease exposure (Graham and Adrian-zen, 1971, 1972; Winick et al., 1975; Lien etal., 1977; Goel et al., 1981; King and Taitz,1985; Mjones, 1987; Schumacher et al., 1987;Steckel, 1987), supplemented with food (Su-per et al., 1990), or treated for disease(Tanner, 1981). Secular trends of increasedheight for age and earlier maturation havebeen reported for populations where im-proved conditions persist across generations(Eveleth and Tanner, 1990). If environmen-tal change in early childhood can increasegrowth velocities to allow partial or com-plete catch-up among those children, thenwe must infer that the conditions of olderDatoga children do not improve sufficiently

to allow catch-up. Thus, although Datogachildren may experience periods of higher-than-normal growth velocity when recover-ing from illness or undernutrition, thesemay not be of sufficient frequency or dura-tion to compensate for the deficits accrued.This hypothesis assumes full catch-up ispossible, but is not observed because theenvironment and diet remain the samethroughout the life span (Golden and Golden,1991). Further research is needed to deter-mine whether the lack of catch-up growth inlater childhood is attributable simply tocontinued inadequacy of food intakes andhigh infection rates among older children. Itis also possible that increased energy de-mands of herding work and arduous house-hold maintenance tasks such as collectingwater and fuel wood act as further stresseson older children and contribute to stunting(Satyanarayana et al., 1986; Spurr, 1987;Sellen, 1998a).

Fig. 6. Comparison of mixed-longitudinal estimates of growth in weight of east African pastoralchildren. Data on settled Turkana from Little and Gray (1990a), nomadic Turkana from Little et al.(1983), and African Americans from Frisancho (1990). a: Girls. b: Boys.


Despite the apparent lack of catch-up inchildhood and the early teen years, data onadult stature among Paranilotic pastoral-ists suggest that delayed initiation or prolon-gation of the adolescent growth period canrecuperate a proportion of early growth defi-cits. Apparent evidence of catch-up growthexists for some populations with demonstra-bly delayed maturation, notably Americanslaves (Steckel, 1987) and the Turkana pas-toralists described by Little et al. (1983).Continued growth beyond 17 years (whenreference populations approach an asymp-tote for stature) has been reported in anumber of (mostly rural) populations (Bowieet al., 1980; Kulin et al., 1982; Steckel,1987). Although the Datoga, Turkana (Gal-vin et al., 1994), Borana (Galvin et al., 1994),Maasai (McCabe et al., 1989), Bororo (Loutanand Lamotte, 1984), Fulani (Hilderbrand,1985), Kel Tamaheq (Wagenaar-Brouwer,1985), Rendille (Nathan et al., 1996), andother populations are stunted during child-hood and adolescence, cross-sectional stud-

ies indicate that populations move back tothe reference median range of stature byadulthood (Little et al., 1983; Sellen, 1996).For example, at 12 years of age, Datoga girlswere on average 17.1 cm shorter than Afri-can American girls. The observed meanheight for Datoga women (158.8 6 6.2 cm,n 5 216) is only 2.7 cm less than that ofAfrican American women 18–74.9 years ofage (Frisancho, 1990; Sellen, 1995). Simi-larly, although at 12 years of age Datogaboys are on average 8.7 cm shorter thanAfrican American boys, the observed meanheight for Datoga men (169.6 6 6.4 cm, n 520) is only 4.6 cm less than that of AfricanAmerican men 18–74.9 years of age. Thus,among the Datoga, delayed puberty mayfacilitate catch-up in stature by extendingthe time window for skeletal growth. Oneinterpretation of the increased deficits ob-served among teenagers in all measures ofbody size relative to the reference popula-tion is that they result from delayed matura-tion.

Fig. 7.

202 D.W. SELLEN

This interpretation is potentially flawedbecause it relies on US reference data tomake inferences about catch-up growth fromcross-sectional data, and takes no account ofpossible ethnic or genetic differences in keyaspects of adolescent growth (Martorell etal., 1994). In order to properly assess theextent to which catch-up is occurring, it isnecessary to know whether the ‘‘height po-tential’’ of these children is similar to that ofthe reference (Golden, 1994). It has beensuggested that Nilotic and Nilo-Hamiticadults may be genetically predisposed to betaller than standards due to differences inrates of growth, length of the growth period,and timing of puberty (Eveleth and Tanner,1990). The observation that achieved meanheights of adult African pastoralists arerather similar to those in the internationalstandards (Sellen, 1996) does not rule outthe possibility that environmental factorsconstrain expression of a differing geneticpotential. However, there is no direct evi-

dence that African populations are geneti-cally predisposed towards delayed matura-tion relative to other populations. Since thegrowth patterns ofAmerican black and whitepopulations are very similar during adoles-cence (Frisancho, 1990), it is plausible tointerpret the growth patterns of the Datogaas reflecting a failure to catch up on earlygrowth stunting during middle childhoodand possibly a delay in adolescent growthspurt.

It is unfortunate that reliable maturitymeasures could not be collected during thesurveys yielding this sample, so that we canonly speculate on the timing of puberty.Since current consensus is that skeletalmaturation is usually not delayed to any-where near the extent of linear growth, sothat the actual period of growth is notsufficiently extended to allow compensationfor growth deficits (Proos et al., 1991; Proos,1992; Martorell et al., 1994), this aspect ofDatoga growth warrants further investiga-

Fig. 7. Comparison of mixed-longitudinal estimates of growth in height of East African pastoralchildren. Data on settled Turkana from Little and Gray (1990a), nomadic Turkana from Little et al.(1983), and African Americans from Frisancho (1990). a: Girls. b: Boys.


tion. The present data suggest that muchgreater delays and adolescent deficits mayoccur among boys. The increases in upperarm fat observed after 8 years in girls and 11years in boys may correspond to the preado-lescent or adolescent increase in adiposityobserved in Western populations (Fig. 9).For girls, the increase in mean height andits variance at 13 years may result from agrowth spurt in height at 12–13 years, butsample sizes are small. The mean height foradult women in this population (158 cm)appeared to be achieved by about 18 years ofage (Table 2), the same age as in the multi-ethnic US reference. Among boys there islittle indication of an increase in heightvelocity between 13–16 years. Indeed, thevery low mean height at 16 years, whichfalls at only the 1st percentile (80% of stan-

dard median), may result from a signifi-cantly delayed growth spurt. For boys toreach adult heights, growth must continuefar beyond 18 years. The exceptionally lowmean weights among teenagers are alsoconsistent with the hypothesis that growthis further compromised during early adoles-cent years, adding to the weight deficitsalready established in early childhood.

It is possible that both a cohort effect andundersampling of larger older children con-founded the mixed-longitudinal presenta-tion of the data. A cohort effect might ac-count for the greater growth deficits amongchildren born before 1976, and particularlyamong boys born in the late 1970s. Ethno-graphic research failed to reveal any signifi-cant events that could be inferred to haveimproved the relative growth status of chil-

Fig. 8. Age distribution of adiposity in Datoga children.

204 D.W. SELLEN

dren born after that date and surviving tomeasurement, such as reduction in the fre-quency or severity of droughts or livestocklosses due to raiding or epidemics. The pat-terns might also be attributable to biasedsampling of more poorly growing children inthe community, perhaps because they weremore likely to be found in the vicinity of thehomestead rather than to be out workingwhen the researchers visited. This is un-

likely because, based on census data col-lected for all households included in thesurveys, anthropometric coverage of olderchildren was almost complete.

In many regards, the Eyasi Datoga maybe a good model for many other Africanpastoral populations, and inferences drawnfrom results of this study may be valid in awider context. However, children in the EyasiDatoga population appear to fall towardsthe lower end of the observed range ofvariation in anthropometric status amongAfrican pastoral populations (Galvin et al.,1994; Sellen, 1996). It is most parsimoniousto interpret variation in pastoral growthpatterns as the result of underlying physi-ological responses of individuals to poornutrition and/or disease stress rather thangenetic factors. It is not clear why the Da-toga, despite being taller and heavier for ageas children, become shorter than the Maa-sai, Turkana, Tutsi, and other nomadic pas-toral as adults. It is likely that a deficiency

Fig. 9. (See legend page 206.)

TABLE 3. Estimated point prevalence of illness amongchildren age 0–3 years

Primary symptom cluster (based onpooled monthly caregiver assessments

for the previous 24 hr)

Illnessprevalence(% of dayssampled,n 5 186)

Fever/malaria 14.5Respiratory (6fever) 11.3Other 15.3Diarrhea without other symptoms 1.0Total illness prevalence 42.1Total nondiarrheal illness prevalence 41.1Combined diarrhea with other symptoms 29.6


of type II micronutrients (Golden, 1988,1997; Brown, 1991; Hambidge, 1992) is lim-iting growth to a greater extent among theDatoga, who have a remarkably monotonousdiet based on maize with only infrequentconsumption of meat, vegetables, and rela-tively lower intakes of milk products. Thesex difference may indicate that zinc inparticular, available mainly from meat, lim-its growth, because the effects are alwaysgreater on males (Walravens et al., 1989).

CONCLUSIONS

Cross-sectional anthropometric observa-tions show that the growth status of Datogachildren is generally very poor relative toWestern reference data, but may be typicalof African pastoralists. Most of the growthdeficits are established in the first 2–3 yearsof life. This may be a critical period in whichthe behaviors of Datoga parents might moststrongly influence the survival of their off-spring. Catch-up growth during later child-

hood, if it occurs at all, is not sufficient toovercome the growth deficits established inthe early years, and there is a strong patternof increasing deficits with age relative toreference populations. Some unusual pat-terns of teenage growth may indicate matu-rational delays and an extended skeletalgrowth period. Alternatively, although we donot yet have data to assess the relativeimportance of energy balance, micronutri-ent supply, and disease factors in the etiol-ogy of growth retardation, increased stunt-ing among teenagers, particularly boys, maybe a specific result of the type of labordemands placed on them. Further work isneed to test the hypothesis that puberty isdelayed among the Datoga and to investi-gate the interactions of genetic and environ-mental factors. These observations have im-plications both for understanding the biologyof the pastoral adaptation in human evolu-tion and for nutrition and developmentpolicy. We predict stronger selection for pa-

Fig. 9. Upper arm composition of American and Datoga children. a: Girls. b: Boys.

206 D.W. SELLEN

rental investment in younger offspring insocieties following an arid pastoral subsis-tence strategy. We also predict that interven-tions to improve growth performance andnutritional status of children in pastoralpopulations would be most effective if tar-geted at the very young.

ACKNOWLEDGMENTS

The Tanzanian Research Council for Sci-ence and Technology and local village chair-men granted permission to carry out theresearch. My thanks go to the communitiesand families who participated. The Univer-sity of California at Davis provided institu-tional support during analysis. The authorthanks Momoye Bashgei Merus and DanielaSieff for assistance in the field, and NicholasB. Blurton Jones, Kathryn G. Dewey, Mo-nique Borgerhoff Muder, and two anony-mous reviewers for helpful comments onearlier drafts.

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growth patterns among seminomadic pastoralists (datoga) of tanzania

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