The costs and benefits of kin

THE COSTS A N D B E N E F I T S OF KIN

Kin Networks and Children's Health among the Pimbwe of Tanzania

Craig H a d l e y University of California, Davis

In this paper data from a Tanzanian horticultural population are used to assess whether mother's kin network size predicts several measures of children's health and well-being, and whether any kin effects are modified by household socioeconomic status. This hypothesis is further tested with a questionnaire on maternal attitudes towards kin. Results show small associations between measures of maternal kin network size and child mortality and children's growth performance. Together these results suggest that kin positively influence child health, but the effects are small and it is unlikely that the high prevalence of undernutrition observed in this setting is influenced by the availability of kin.

KEY WOt~OS: Africa; Child care; Nutritional status; Social support; Tanzania; Underweight

Assumptions about the relationship between kin networks and children's health and well-being underlie numerous models in human behavioral ecology. This is because the theory of kin selection suggests that, ceteris paribus, individuals will preferentially assist their relatives since by doing so they place more of their own gene copies into future generations (Hamilton 1964). It is assumed, therefore, that women should prefer to remain in their natal villages, near their natal kin, because by leaving, especially "for social species such as humans, dispersers may directly suffer due to lack of mutual support provided by kin in the new locale" (Fix 1999). Following this logic, it has recently been hypothesized that assistance from kin may underlie the unique life history of humans. In

Received September 29, 2003; accepted December 15, 2003; revised version received January 28, 2004.

Address all correspondence to Craig Hadley, Population Studies and Training Center, Box 1836, Brown University, Providence, R! 02912-1836. Ernail: Craig_Hadley @ brown, edu

Copyright �9 2004 by Aldine Transaction, New Jersey Human Nature, Vol. 15, No. 4, pp. 377-395. 1045-6767/98/56.00 + .15

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378 Human Nature, Vol. 15, No. 4, 2004

particular, it has been argued that the relatively (compared to animals of similar body size) short interbirth intervals and "early" age of weaning that typify the human life history are the result of maternal kin subsidizing the cost of reproduction (Hawkes et al. 1998; Sear et al. 2000). Much of the focus has been on the role maternal grandmothers might play in influencing children's health and well-being. However, as originally proposed, the influence of grandmothers was hypothesized to be important only in situations where resources were difficult for juveniles to acquire (Hawkes et al. 1998). This condition is likely not met among many agr icul tural is t and hort icul tural is t peoples . Indeed, e thnographic observations from non-foraging peoples in sub-Saharan Africa repeatedly stress the important caregiving roles of other, younger female kin, especially children (Borgerhoff Mulder 1985; LeVine 1994; Weisner and Gallimore 1977).

A second consideration, and one that has been examined less, is that in resource-scarce areas having too many kin may be detrimental to reproductive fitness. This is because in communities where kin relationships create obligations, having too many kin may result in excessive demands on resources, thereby breeding competition, not cooperation. This intro- duces the possibility that living near closely related kin may in fact be costly, not beneficial, to reproductive fitness because kin may be able to make demands on food and other resources critical to children's health and well being. When this is the case, kin selection will be relatively unimportant relative to competition over scarce resources. Indeed, empirical and theoretical studies from the animal behavior literature suggest that the conditions under which kin selection is favorable are far more limited than previously thought (Armitage and Schwartz 2000; West et al. 2001).

In this article, data from a Tanzanian horticultural population, the Pimbwe, are used in a preliminary attempt to clarify the issues raised above. The objective of this study was to explore the association between various measures of a woman's kin network and her children's health from cross-sectional and longitudinal perspectives, and to assess whether any relationship was modified by household wealth. A secondary objective was to test whether or not Pimbwe women recognized the costs or benefits of living near their kin group.

Evolutionary anthropologists have shared with anthropological demog- raphers a keen interest in contextualizing demographic outcomes (Kertzer and Fricke 1997). Indeed, a major theme in anthropological demography is the relationship between kin networks and reproductive behaviors (Das Gupta 1997), and evolutionary anthropologists have made significant con-

The Costs and Benefits of Kin 379

tributions to this area by drawing on evolutionary theory to make specific predictions about which kin are expected to be more productive in promoting the social and biological reproduction of the family. A key predic- tion that has been tested is the differential influence of male and female kin on demographic and health outcomes. For example, using historical data and rigorous statistical methods, Sear and colleagues (2000, 2002) showed that Gambian children with living maternal grandmothers faced lower odds of dying and had better nutritional status than children without living maternal grandmothers. Female kin were also associated with greater reproductive success among Kenyan Kipsigis. In that case, men with relatively more sisters had more children surviving to age five. Borgerhoff Mulder (1998) points out, however, that using survival to age five as an outcome obscures the mechanism that may ultimately promote child survival. In their study of Ache demography, Hill and Hurtado (I 996) also tested for the hypothesized kin effects on child mortality and found little evidence of an effect from extended kin. They rightly point out the difficulties of identifying kin effects with an observational study design precisely because if a child's health begins to falter, kin should assist that child, thereby obscuring any kin effect. In addition to measurement issues, these studies and others (see, for instance, Chert et al. 2000) suggest that the influence of different kin groups may vary with local ecology and culturally specific gender roles. The limited number of studies, however, makes it difficult to test hypotheses about the socioecological conditions in which specific kin are likely to be influential in improvising child health.

Despite difficulties in measurement, the available studies also highlight the potential role of extended kin networks as an important set of variables to explain variation in demographic and health outcomes within populations. In the present study, the influence of kin was hypothesized to be an important determinant of demographic and health outcomes within a small East Africa rural community. It was also hoped that multiple measures of the relationship between kin and demographic and health outcomes would be helpful in revealing any interaction between them.

STUDY POPULATION

The study site sits in southwest Tanzania's Rukwa valley (Figure 1). The area is topographically flat and characterized by dry, sparse woodland. The Rukwa region is one of the least developed in terms of state infrastructure and is among the poorest in all of Tanzania (World Bank 2000). Throughout the region, roads are dirt and the vast majority of


villages have no electricity or running water. Paradoxically, the Rukwa region is one of the largest producers of corn in the country and is considered by some to be Tanzania's granary, but because of the distance to the railway and the largest city (Dar es Salaam), the selling of crops brings little profit to local farmers (World Bank 2000). There are a few small stores, a health clinic, and some government offices for the district. A larger health clinic is located approximately i I km away and more substantial hospitals are located in the larger towns of Mpanda and Sumbawanga--a

Figure 1. Map of Study Area

$HINYANGA ARUSHA

KIGOMA

TANGA ~ PEMBA

Study a r e a MBEYA

LINDI

RI.WUMA

0 100 km


4- to 6-hour road trip by car. In this area of Rukwa, rainfall begins in November and continues until March or April. Malaria is endemic to the area.

Until the 1970s, the Pimbwe, a Bantu group with the longest known history of residence in the area, were mixed hunter-horticulturalists and goat herders living in widely scattered settlements (Willis 1966). In the 1950s, a large block of land was set aside for a game reserve, which was expanded into Katavi National Park in the 1970s. Because of this expan- sion, hunting is now illegal and therefore no longer plays a dominant role in Pimbwe culture, although it is still actively practiced. The Pimbwe now live in approximately ten densely settled villages ranging from 240 to 700 households. Houses are constructed of mud bricks and thatched roofs or, more rarely, fire-burned bricks and tin roofs. Marriages are monogamous and residence patterns are neolocal--upon marriage husband and wife move into a new house, although in such small villages it is difficult to move very far from one's relatives. Households are generally quite small, with a modal size of four people--although they can be as large as thirteen.

All households practice subsistence horticulture on land that is typically passed on through the paternal line. Agricultural life follows the rains, and farms are typically planted in November, weeded in January and February, and tended in March. They produce maize by late March. The primary harvest occurs around July, and food stocks are steadily de- pleted until the following March. Maize is by far the most prominent crop. Peanuts and some variable cash crops are also farmed by a majority of the households. Fields are on average 1-3 acres, although there is re- portedly marked variability in productivity across the landscape and farming is most often done with hoes. Off-farm income-generating activities in- clude the sale of homemade beer, the sale of honey (March), and the harvesting and sale of timber. A small pilot time allocation study during the dry season confirms ethnographic suspicions that women engage in considerably more activities that could be broadly construed as "work," such as fetching water, carrying firewood, and doing household chores, than men (Hadley, unpublished data).

METHODS

Fieldwork was carried out in three periods between September 2000 and February 2002. All interviews were conducted in the presence of a local assistant and were always in Swahili. A census of three neighborhood blocks was made in September 2000, and the primary reproductively active

382 Human Nature, Voi. 15, No. 4, 2004

woman (n = 132; all monogamous, all parous) in each house participated in a life history interview. Data on place of birth, kin networks, presence of parents in the study area, and household wealth holdings were gathered. These data were cross-checked and updated in two additional surveys in 2001 and 2002. From these data measures of fertility and child mortality were calculated. Measures of kin network size are also taken from these data. For each mother the following information was used as predictor variables: (I) number of brothers and sisters living in the study area (defined as living in the village of Kibaoni, or one of three other nearby villages), (2) presence of mother in the study area, (3) presence of father in the study area, and (4) whether she was born in the study area or not. Place of birth was used a proxy for number of kin in the network in the analysis regarding reproductive outcomes. For analyses of current nutritional status (i.e., weight-for-age), kin network was defined as the number of full brothers and number of sisters a mother had living in the study area. Household socioeconomic status was defined on the basis of the amount of land currently under cultivation, the number of material items owned (bike, radio, drum for brewing beer, and a watch), and the amount of livestock. Because these were all highly intercorrelated, principal components analysis was used to extract a single factor; this is termed socioeconomic status (SES) in the analyses below.

A cross-sectional anthropometric survey was conducted in September 2000 (dry season) in the village of Kibaoni to collect baseline data on children's nutritional status. Nearly all households visited to obtain demographic information participated in the survey. Households that did not participate differ in the average age of household members; most non-participating households had no young children in their household. Children's height and weight were measured using standard procedures (Shorr 1986); very young children were often not measured for length because of mothers' reluctance to allow their children to be measured. Children were minimally clothed, and always shoeless. Height measure- ments were made using a standard height board and were taken to the nearest 0.1 cm, and weight was measured to the nearest 0.1 kg using a Seca electronic scale. All participants received a meal following the weigh- ing.

The children's anthropometric data were converted to z-scores using a computer program (Epi-Info) and the following measures of nutritional status were created: height-for-age z-score (HAZ), weight-for-age z-score (WAZ), and weight-for-height z-score (WHZ). Children were then classi- fied on the basis of whether or not they were stunted (defined as having a HAZ less than -2), underweight (defined as a WAZ less than -2), or


wasted (defined as a WHZ less than -2). The z-scores represent standard- ized deviations from a reference median, which is constructed by measur- ing healthy age- and sex-matched children whose growth has been largely unaffected by undernutrition and frequent bouts of illness. In this paper, WAZ is used as the primary outcome measure because a low weight-for- age value, or underweight, has been consistently shown to predict risk of mortality (Pelletier 1994; Schroeder and Brown 1994) and is one of the greatest contributors to the global burden of disease (Ezzati et al. 2002) since malnutrition increases susceptibility to infectious diseases.

Following the initial cross-sectional survey, a sample of 55 households was chosen through a nonrandom sampling strategy to participate in a longitudinal study of children's growth. These households were chosen because they had at least one child under age five; later analyses showed that they encompassed the village's range of variation in wealth and kin network size. The children from these households were measured in the September 2000 survey and again in February 2002, a 16-month period. Unfortunately, length was measured in only a very small sample of children in the first survey and therefore I was unable to calculate change in children's height. Children's weight gain was calculated as the difference in weight between the two anthropometric surveys.

Lastly, in 2001 a survey instrument was administered to a sample of 81 mothers selected randomly from a household census list using a random number table (Bernard 1994). These mothers were living in three of the four neighborhood blocks and were questioned about their attitudes regarding health care, feeding strategies during illness, and their thoughts on kin. Specifically, mothers were asked to choose whether they thought it was "good" or "bad" to live in the same village as their kin. This was followed by an open-ended question asking women to expand on their answer.

Multivariate models were used to assess the association between women's place of birth and their fertility, and child mortality. T-tests and multivariate regression were used to test for associations between children's WAZ and the measures of kin network, and logistic regression was used to assess the variables associated with mothers' attitudes toward living near their kin. Probabilities less than 0.05 are considered statistically significant, and values between 0.05 and 0.10 are considered marginally significant.

RESULTS

The best strategy to assess whether women with larger kin networks experience lower child mortality would be to have time-varying covariates


and age-specific fertility and mortality data (see, for example, Sear et al. 2000). Unfor tunate ly , these data are incredibly diff icul t to obtain retrospectively. Here an alternative strategy is used, which carries with it certain limitations. Mother's place of birth is used as a proxy for her kin support network. Indeed, women born in the study area had significantly more adult brothers and sisters as well as siblings younger than 18 (subadults) available to them. This suggests that place of birth is an appropriate proxy measure of kin network. Thus, for the analysis of reproductive outcomes the proxy is used because time-varying measures of kin networks were not collected.

Women who had not yet given birth to a child or whose youngest child was under five years were excluded, thereby reducing the sample to 101 women, because a primary outcome measure for this research was survi- vorship to five years. Of these 101 women, 47% were born in the study area, and there was no difference in age between mothers born in the study area or elsewhere. Mothers born in the study area reported a slightly greater number of total live births and a slightly smaller number of children who had died before age five. A multivariate regression analysis (Table 1) revealed that the cumulative effect of these slight differences was small, but a statistically significantly greater number of children of women born in the study area lived past the age of five (p = 0.04). This effect held even after controlling for the obvious influence of the number of live births reported (p < 0.001).

To further explore the possible influence of kin on children's health, the cross-sectional data were analyzed to test for possible associations between children's weight-for-age z-score (WAZ) and kin network size. One hundred fifty-eight children from 132 mothers were included in the analysis. Children younger than three years of age were excluded from this analysis because most of those measured were part of the cohort dis- cussed below. As is typical for children in rural Tanzania, anthropometric indices were quite low and showed a marked departure from the reference median. For the children in the middle childhood group (3-10 years old) mean values of WAZ, HAZ, and WHZ were -1.29 (_+ 0.97), -1.49 (__. 1.06),

Table 1. Multivariate Regression Model of the Factors Associated with the Number of Children Living Past Age Five (r 2 = 0.80, n = I01 mothers)

Variable Estimate Std. Error p

Intercept 1.32 0.28 0.01 Mother born outside study area? -0.45 0.22 0.04

Number of live births 0.81 0.04 <0.0001


and -0 .32 (_ 0.93). The prevalence of stunting was 30% and underweight , 27%. Approximately 4% of children were categorized as wasted. There were no differences between the sexes in the prevalence of any indicator.

The association between chi ldren 's weight-for-age z-score and the kin variables was inconsistent, suggesting that not all kin are equally beneficial. For chi ldren three and older , there was no associa t ion be tween chi ldren 's WAZ and their mother ' s place of birth (mother born in study area [ -1 .34 _ 0.95] vs. born e lsewhere [-1.27 __. 0.95], t = -0 .47 , p = 0.63). Neither was there an association between the presence of maternal grandmother (grandmother here [-1.29 _+ 0.95] vs. grandmother not here [-1.30 _+ 0.95], t = 0.09, p = 0.95) or maternal grandfather (grandfather here [ -1 .40 _ 1.03] vs. grandfather not here [-1.18 a: 0.86], t = -1 .44 , p = 0.15). A multivariate model, however, showed positive effects of both household socioeconomic status and total number of mother ' s brothers

Figure 2. Interaction between household SES and kin network size on model predicted children's weight-for-age z-score. WAZ as predicted by the regression equation is used to more clearly show the relationship between the variables. For ease of interpretation continuous variables are represented here as categorical variables following the procedure outlined by Aiken and colleagues (1991). The 25 ~h, 50'", and 75 th percentiles of SES have been plotted here to represent low, medium, and high levels of SES. The 25'h and 75'" percentiles for kin network size are presented here as "few" and "many" kin.

n

-2

, j .

t '

4r

~ ~ Low SES

- ~ - - - M e d S E S

O . ~ - - Hiah SES

Few kin Many kin


Table 2. Variables Associated with Children's (3-10 year of age) WAZ in the 2000 Cross-sectional Survey. Sister refers to the number of sisters a child's mother reports as currently living in the study area (r a = 0.14, p = 0.002, n = 158 children).

Variable Estimate Std. Error

Intercept -0.99 0.24 0.0001 Sex (F) -0.098 0.13 0.47 Child's age (months) -0.007 0.0026 0.005 SES 0.0053 0.0020 0.01 Sister 0.10 0.044 0.02 SES * sister -0.0009 0.0004 0.04

and sisters on children 's WAZ. Interestingly, a very weak, but statistically significant, interaction term between household SES and kin network size suggested that the relationship between WAZ and kin network size varies across household economic status (p = 0.04; Figure 2). To achieve a better understanding of this interaction, the continuous variables are represented in Figure 2 as categorical variables following the procedure outlined by Aiken and colleagues (1991). The 25 th, 50 th, and 75 'h percenti les o f SES have been plotted here to represent low, medium, and high levels of SES. The 25 th and 75 th percentiles for kin network size are presented here as " few" and "many" kin.

Further disaggregating the kin network term revealed that the number of mother ' s sisters, but not brothers, was significantly associated with the positive effect of the kin network term. The SES and the interaction term were also significant predictors (Table 2). Disaggregating the data to com- pare the association between mother ' s adult and subadult sisters and chi ldren 's WAZ scores showed that the parameter estimates for adult and subadult sisters were each positive but alone they were no longer statistically significant.

Broadly similar results were obtained from the longitudinal data set. Preliminary analyses revealed no effect o f household SES on chi ldren 's weight gain so this term was not added to any of the models (p >> 0.50). In a multivariate regression model controlling for baseline age and child sex (F = 2.92, r 2 = 0.17, p = 0.04), children with mothers who had more kin in the study area gained more weight across the 16-month study period than children with fewer kin in the village (partial p = 0.02; Figure 3). Disaggregating the kin term and estimating three additional models showed


Figure 3. Children's (<36 months) gain in weight (kg) across 16 months against their total number of maternal aunts and uncles. Children with more aunts and uncles gained more weight across the period (r 2 = 0.17 p = 0.04).

6

bO 4"

r

r

3

0

0

0

O

0 0

0 O 0 O

0 0 O ~

o o

0 6 0

0 0 0 0 0 0

o o (3

, , , , 1 , , , , i , , , , i , , , , i , , , , I , , , , i , , , , I , , , ' 1 ' , , , 1 ' ' ' ' 1 ' ' ' ' 1 ' ' ' '

0 1 2 3 4 5 6 7 8 9 10

Mother 's number of brothers and sisters

11 12

Table 3. Regression Model Showing That Children with More Subadult (<18 years of age) Maternal Kin Gained More Weight across the 16-Month Period (r 2 = 0.14, p = 0.02, n = 58)

Variable Estimate Std. Error p

Intercept 3.24 0.32 <.0001

Sex (F) --0.19 0.28 0.51

Child' s age (months) -0.01 0.14 0.26

Subadult female kin 0.35 0.02 0.02


that the first model including only brothers was not significant (F = 1.67, r 2 = 0.08 p = 0.19). The second model including the term for sisters was significant (F = 3.49, r2= 0.16, p = 0.02), and a third model investigating the effect of subadult female kin showed that the female kin effect was driven almost entirely by the number of sisters a mother had that were under 18 years of age (F = 3.17, r2= 0.14, p = 0.02; Table 3).

DO PIMBWE WOMEN RECOGNIZE THE BENEFITS OF KIN?

These data suggest that, for the majority of mothers, having kin living in the study area is associated with increasing numbers of children surviving to age five, having greater relative weight, and having greater weight gain. Further, the data from the cross-sectional study suggested that this effect was modified by household wealth: wealthy households benefit the least from kin and poor households the most. To assess whether Pimbwe women recognized these beneficial effects of kin and the tradeoff that may occur with increasing SES, women's responses to the question of whether they thought it was "good" or "bad" to live in the same village as one's kin were analyzed.

Answers to this question were nearly split and highlight the conflicting feelings toward kin. Fifty-seven percent of women said that they thought it was "good" to live near kin and mentioned the resources that kin could provide. For example, they cited general help, "Food, money, and help during times of illness," "Food, money, and [help] during harvest," "Help without any problems," and "If you're hit by your husband, you can go to your parents' house." The other group replied that living in the same village as one's kin was "bad," and women almost unanimously cited "conflict" or "problems will arise all the time" as to why this was so. These responses highlight that women see kin as individuals who can provide goods and services, but also recognize that such behavior can promote conflict.

To test whether women's responses to this question conformed to ex- pectations derived from the above results, the number of children each woman currently had living in their house and their household SES were entered into ~i stepwise logistic regression. The number of children in the household and the household's SES were predictors of women's response to this question (Table 4). As expected, women with more children in their household (and presumably able to gain greater benefits from kin) were more likely to respond that having kin in the village was "good." Women from households with high SES were slightly more likely to respond that having kin in the same village was "bad," and alternatively,


Table 4. Results of Logistic Regression on Whether Mothers Thought It Was "Good" or "Bad" To Have Kin Living in the Same Village (r 2 = 0.1 l ,p = 0.01,n=81)

Variable Exp(B) Estimate Std. Error Z 2 p

Intercept -0.17 0.52 0.11 0.73

No. of children in 0.25 0.12 4.95 0.02 household

SES -0.02 0.011 3.7 0.05

women from lower SES households were slightly more likely to report having kin in the same village was "good." These Pimbwe women appear to be cognizant of both the costs and benefits of living near one's kin.

DISCUSSION

The results of this study show statistically significant relationships between mother's female kin network size (defined as the number of full brothers and sisters) and children's relative weight and young children's weight gain. Women born in the study area, who are therefore more likely to have kin present in the village, also had more of their children survive to age five. Results from the survey on women's attitudes towards kin showed that women are apparently cognizant of the benefits that kin bring, as well as the possible tradeoff that comes with relatively high SES. Women with more children in their houses were more likely to respond that having kin in the village was "good" whereas women with high SES were more likely to say that having kin in the village was "bad.'" Together these results are consistent with the hypothesis that kin, primarily mother's sisters, are influential in increasing the health of children within this study population.

These results are also consistent with broader cross-cultural findings showing that female kin are apparently more important in affecting children's health than male kin (Sear et al. 2002; Wilson 1998). They are also consistent with findings that young females, often kin, are the primary caretakers in many societies (Bove et al. 2002; Turke 1988; Weisner and Gallimore 1977). A similar sister-effect to that shown in this study was found among Hungarian Gypsies. Here, a mother's own sibship size influenced her fertility, mainly owing to the effect of sisters: women with more sisters had greater fertility, but brothers had no effect (Bereczkei 1998). The results from a time allocation study also showed that women,


much more so than men, engaged in substantial amounts of child caretaking. These results suggest that it may be young women who are assisting in increasing women's fertility through subsidizing childcare. Unfortu- nately, time allocation data were not collected for young children in this Pimbwe sample. Based on field observations, however, it is impossible not to arrive at the conclusion that young girls engage in extraordinary amounts of childcare, whether for their mothers or others. Children were routinely observed being left at the homes of kin while mothers went to the field, to collect fuel wood, or to fetch water from the well.

The relationship between mother's place of birth and number of children surviving to age five is also consistent with the literature on dispersal and women's power and autonomy as well as empirical results from the sociological literature (Dyson and Moore 1983). Smuts (1995), drawing on the nonhuman primate literature, argues that female dispersal un- dermines women's power and autonomy because it dislocates women from a supportive kin group. What aspect of support is missing for women who marry into a new village remains to be identified, but some clues emerge from a small questionnaire about help and assistance administered to the 55 mothers from the longitudinal study as part of a pilot study on helping behavior (Hadley, unpublished data). Women who were born in the study area were significantly less likely to report having difficulty borrowing money during times of need (Z 2 = 6.42, p = 0.01). Mothers also stated that borrowing money was the most important form of assistance because it was crucial for purchasing medicines for severely ill children. In this cash-poor area the ability to borrow money for medicines during bouts of illness may be particularly important.

The results also suggested a weak interaction between household SES and female kin network size. Given the small effect size caution should be used when interpreting this term. It does, however, suggest that per- haps the relationship between number of sisters and children's WAZ is contingent upon household socioeconomic status. With such a small sample, it is difficult to interpret the substantive meaning of this interaction. Does having many female kin raise the health of poorer children, or bring the health of the wealthy down? That is, do kin networks ameliorate the negative effects of poverty or increase demands on "wealthy" women, which in turn lower children's WAZ? It is difficult to identify which of these hypotheses is correct given the observational nature of the study (see chapter 13 in Hill and Hurtado 1996 for an excellent discussion of the difficulty in detecting kin effects with observational data). Similar results have been reported among the Datoga, a pastoralist group in northern Tanzania (Sellen 2003). Based on a study of wealth and children's


nutritional status, Sellen concludes that greater levels of wealth may in fact be costly to health, rather than being beneficial to women and their children, and he likens the excessive demands of kin to "tolerated theft." Under conditions of tolerated theft, defending resources from competi- tors is more costly than the benefits gained from those resources (Blurton Jones 1984). In many cases, demands made by poorer kin on wealthier kin may be too costly to deny--costs that may play out in poor child health or social costs brought on by gossip. It is important to reiterate that the effect size of the interaction in the current study was very small.

It is also of interest to highlight two categories of kin that were not associated with greater nutritional status: brothers and maternal grandmothers. There are several possible reasons for the lack of a brother effect, although the two that are most plausible are that men generally engage in little direct childcare and they may use resources at their disposal towards ends other than promoting child growth. Men could provide resources other than childcare, such as purchasing medicine, but the evidence suggests that this is rare. Indeed, some evidence suggests that men, more so than women, use resources to purchase luxury goods and that this may negatively influence children's anthropometric outcomes (Haddad et al. 1997).

The presence of maternal grandmothers was not associated with their grandchildren's nutritional status. There are several possible reasons for this result. First, in this study no data were available on the reproductive status of the maternal grandmother. This is a potentially important limita- tion because theory would suggest that grandmothers who are still reproductively active may be more interested in allocating their time and effort toward their own children, and should not be expected to shunt their energy towards grandchildren until they have stopped reproducing. Sear and colleagues (2000) have provided data which support this suggestion by showing that at three and five years of age, Gambian children with reproductively active grandmothers were shorter than children with non- reproductive grandmothers. However, no clear difference was found between these groups with regard to child mortality. More likely, and consistent with Hawkes's original formulation of the "grandmother hypothesis," is the possibility that, in this Pimbwe population, grandmothers truly have no effect on children's health because resources are n o t

difficult to extract, the critical condition proposed by Hawkes. Ethno- graphic observations of Pimbwe grandmothers suggest that they engage in only very limited childcare, and indeed very little economic activity.

It is difficult to say precisely what mechanisms might underlie these small kin effects. A distinct possibility is that simple counts of kin are


poor predictors of care received, and that a more precise measure indicat- ing both kin size and support received would perform much better at identifying the relationship between kin support and child health. Simple counts of kin, like those used in this study, presume that all potential caretakers have the same influence on child health, although this assumes the quality of care delivered by alternative caretakers is similar (which is not necessarily the case; see Lamontagne et al. 1998). Unfortunately, in the absence of time allocation data, identifying possible caretakers and the amount they invest is incredibly difficult. In this study, all kin were assumed to be equally adept at providing care--a simplistic classification scheme that likely performs poorly in correctly distinguishing those who help from those who do not. One obvious threat to the validity of my coding scheme is that some, if not most, of the children older than eight years spend a substantial portion of their day in school and are therefore unavailable to partake in childcare duties.

In conclusion, the children in this population, like many children in developing countries, suffer from high levels of nutritional stunting and underweight. This study identified small, but statistically significant, associations between mother's kin network size and several measures of child health. Given the small magnitude of these effects, it is unlikely that kin network size makes a significant contribution to the high prevalence of undernutrition in this community or explains much of the variation between children within this community. Moreover, very little data are available from this study to hone in on the mechanisms that may fuel these relatively small associations. Future studies on kin effects would benefit from collecting retrospective data on the presence of various kin throughout the life course. Such data would facilitate more rigorous statistical testing and could probably be fairly easily collected with the use of recently developed event history calendars (Axinn et al. 1999). Future studies should also rely on time allocation data to correctly identify ac- tual caregivers from potential caregivers and to pinpoint the pathways through which kin actually assist. Such data would allow for much stron- ger hypothesis testing about the relationship between kin networks and children's health.

I wish to thank Monique Borgerhoff Mulder, Dan Sellen, Kay Dewey, and three anony- mous reviewers for their thoughtful comments and suggestions on the manuscript. Funding was generously provided by NSF (Grant No. 0001901), the Gifford Center for Population Issues, and University of California, Davis.

Craig Hadley (Ph.D. Anthropology and D.E. International Nutrition, University of California, Davis, 2003) is a postdoctoral fellow in Population Studies and Training


Center at Brown University. His research interests are in children's well-being and nutrition, with a geographic focus in East Africa,

REFERENCES

Aiken, L., S. West, and R. Reno 1991 Multiple Regression: Testing and Interpreting Interactions. Newbury Park,

California: Sage. Armitage, K., and O. Schwartz

2000 Social Enhancement of Fitness in Yellow-Bellied Marmots. Proceedings of the National Academy of Sciences (USA) 97:12149-12152.

Axinn, W., L. Pearce, and D. Ghimire 1999 Innovations in Life History Calendar Applications. Social Science Research

28:243-264. Bereczkei, T.

1998 Kinship Network, Direct Childcare, and Fertility among Hungarians and Gypsies. Evolution and Human Behavior 19:283-298.

Bernard, H. 1994 Research Methods in Anthropology: Qualitative and Quantitative Ap-

proaches. Thousand Oaks, California: Sage. Blurton Jones, N.

1984 A Selfish Origin for Human Food Sharing: Tolerated Theft. Ethology and Sociobiology 5:1-3.

Borgerhoff Mulder, M. 1985 Factors Affecting Infant Care in the Kipsigis. Journal of Anthropological

Research 41:231-262. 1998 Brothers and Sisters: How Sibling Interactions Affect Optimal Parental Al-

locations, Human Nature 9:119-162. Bove, R., C. Valeggia, and P. Ellison

2002 Girl Helpers and Time Allocation of Nursing Women among the Toba of Argentina. Human Nature 13:457--472.

Chen, F., S. Short, and B. Entwisle 2000 The Impact of Grandparental Proximity on Maternal Childcare in China.

Population Research and Policy Review 19:571-590. Das Gupta, M.

1997 Kinship Systems and Demographic Regimes. In Anthropological Demog- raphy: Toward a New Synthesis, D. Kertzer and T. Fricke, eds. Pp. 36-53. Chicago: University of Chicago Press.

Dyson, T., and M. Moore 1983 On Kinship Structure, Female Autonomy, and Demographic Behavior in

India. Population and Development Review 9:35-60. Ezzati, M., A. Lopez, A. Rodgers, S. Hoorn, and C. Murray

2002 Selected Major Risk Factors and Global and Regional Burden of Disease. The Lancet 360:1347-1360.

Fix, A. 1999 Migration and Colonization in Human Microevolution. Cambridge:

Cambridge University Press. Haddad, L., J. Hoddinott, and H. Alderman

1997 Intrahousehold Resource Allocation in Developing Countries: Models, Methods, and Policy. Baltimore: Johns Hopkins University Press.


Hamilton, W. 1964 The Genetical Evolution of Social Behaviour, I & II. Journal of Theoretical

Biology 7:1-52. Hawkes, K., J. O'Connell, N. Blurton Jones, H. Alvarez, and E. Charnov

1998 Grandmothering, Menopause, and the Evolution of Human Life Histories. Proceedings of the National Academy of Sciences (USA) 95:1336-1339.

Hill, K., and M. Hurtado 1996 Achd Life History: The Ecology and Demography of a Foraging People.

New York: Aldine de Gruyter. Kertzer, D., and T. Fricke

1997 Anthropological Demography: Toward a New Synthesis. Chicago: University of Chicago Press.

Lamontagne, J., P. Engle, and M. ZeiZlin 1998 Maternal Employment, Child Care, and Nutritional Status of 12- to 18-

Month-Old Children in Managua, Nicaragua. Social Science & Medicine 46:403- 414.

LeVine, R. 1994 Child Care and Culture: Lessons from Africa. New York: Cambridge

University Press. Pelletier, D.

1994 The Relationship between Child Anthropometry and Mortality in Developing Countries: Implications for Policy, Programs and Future Research. Journal of Nutrition 124: s2047-s2081.

Schroeder, D., and K. Brown 1994 Nutritional Status as a Predictor of Child Survival: Summarizing the

Association and Quantifying Its Global Impact. Bulletin of the World Health Organization 72:569-579.

Sear, R., R. Mace, and I. McGregor 2000 Maternal Grandmothers Improve Nutritional Status and Survival of Children

in Rural Gambia. Proceedings of the Royal Society of London, Series B: Biological Sciences 267:1641 - 1647.

Sear, R, F. Steele, I. McGregor, and R. Mace 2002 The Effects of Kin on Child Mortality in Rural Gambia. Demography 39:43-

63. Sellen, D.

2003 Nutritional Consequences of Wealth Differentials in East African Pastoralists: The Case of the Datoga of Northern Tanzania. Human Ecology 31:529-570.

Shorr, I. 1986 How to Weigh and Measure Children: Assessing the Nutritional Status of

Young Children in Household Surveys. New York: United Nations Department of Technical Cooperation for Development and Statistical Office.

Smuts, B. 1995 The Evolutionary Origins of Patriarchy. Human Nature 6:1-32.

Turke, P. 1988 Helpers at the Nest: Childcare Networks on Ifaluk. In Human Reproductive

Behavior, L. Betzig, M. Borgerhoff Mulder, and P. Turke, eds. Pp. 173-188. Cambridge: Cambridge University Press.

Weisner, T., and R. Gallimore 1977 My Brother's Keeper: Child and Sibling Caretaking. Current Anthropology

18:169-190.


West, S., M. Murray, C. Machado, A. Griffin, and E. Herre 2001 Testing Hamilton's Rule with Competition between Relatives. Nature

409:510-513. Willis, R.

1966 The Fipa and Related Peoples of South-West Tanzania and North-East Zambia. London: International African Institute.

Wilson, A. 1998 The Paradox of Polygyny among the Mamprusi. Ph.D. dissertation, University

of California, Davis. World Bank

2000 Agriculture in Tanzania since 1986: Follower or Leader of Growth? Washington, D.C.: International Food Policy Research Institute.

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