Why pigs are important in Papua? Wealth, height and reproductive success among the Yali tribe of West Papua

Economics and Human Biology 11 (2013) 382–390

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Why pigs are important in Papua? Wealth, height and reproductive success among the Yali tribe of West Papua Piotr Sorokowski a,*, Agnieszka Sorokowska a, Dariusz P. Danel b a b

Institute of Psychology, University of Wroclaw, ul. Dawida 1, 50-527 Wroclaw, Poland Polish Academy of Sciences, Institute of Anthropology, ul. Kuznicza 35, 50-951 Wroclaw, Poland

A R T I C L E I N F O

A B S T R A C T

Article history: Received 6 June 2011 Received in revised form 25 February 2012 Accepted 28 February 2012 Available online 7 March 2012

Many studies have investigated how different variables influence the reproductive success (RS) in the populations of natural birth control. Here, we tested hypotheses about positive relationship between wealth, height and several measures of RS in an indigenous, traditional society from West Papua. The study was conducted among the Yali tribe in a few small, isolated mountain villages. In this tribe, a man’s wealth is measured by the number of pigs he possesses. We found that wealth was related to fertility and number of living children, but not to child mortality in both men and women. Additionally, child mortality increased with the number of children in a family. Finally, we did not observe any relationship between height and reproductive success measures or wealth. We provide several possible explanations of our results and also put forward hypothetical background for further studies of indigenous populations. ß 2012 Elsevier B.V. All rights reserved.

Keywords: Yali Pigs Wealth Height Fertility Mortality

1. Introduction Many studies have investigated how different variables influence the reproductive success (RS) in the populations of natural birth control (e.g., Apicella et al., 2007; Hill and Hurtado, 1996; Mace, 1996a; Smith, 2004). It has been suggested that one of the most important elements related to male RS can be his status and wealth (Trivers, 1972); economically and socially successful individuals outreproduce less successful individuals (Daly and Wilson, 1983; Fisher, 1930; Wilson, 1975). Wealth and status covary with lifetime RS in preindustrial human populations (e.g., Clarke and Low, 1992; Dribe, 2004; Lycett et al., 2000; Pettay et al., 2007; Røskaft et al., 1992; Skjærvø et al., 2011). Additionally, a lot of data confirm the presence of such relationship, at least for males (but not always for females) in indigenous, traditional societies existing

* Corresponding author. Tel.: +48 71 367 20 01/131; fax: +48 71 367 18 14. E-mail addresses: [email protected] (P. Sorokowski), [email protected] (A. Sorokowska), [email protected] (D.P. Danel). 1570-677X/$ – see front matter ß 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ehb.2012.02.008

nowadays (in chronological order: Yomut Turkmen of Iran – Irons, 1979; Ifaluk of Caroline Islands – Turke and Betzig, 1985; Caribbean farmers – Flinn, 1986; Kipsigis of Kenya – Borgerhoff Mulder, 1987; Efe of Zaire – Bailey, 1991; Bakkarwal of India – Casimir and Rao, 1995; Gabbra of Kenya – Mace, 1996a; Mukogodo of Kenya – Cronk, 1991; Dogon of Mali – Strassmann, 1997). Although the relationship between wealth and RS is rather hard to observe in industrialized societies (because of common usage of contraceptives), recent studies have attempted to analyze this phenomenon also in such societies, and some preliminary data demonstrate its existence in males (e.g., Hopcroft, 2006). Another element related to RS is height of an individual. In the context of traditional societies, the majority of studies regarding this relationship concerns women. In !Kung San people (Northern Namibia), shorter women had more children (Kirchengast, 2000). Devi et al. (1985) showed a similar correlation for women from lower casts in India. This result was an effect of both lower fertility and higher mortality of children of taller women. On the other hand, Fielding et al. (2008) did not find any relationship

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between height and RS of Chinese women. At the same time, Sear et al. (2004) showed that although shorter women in Gambia have children earlier, their reproductive success is lower than of taller women, whose children survive more frequently. A similar relationship was observed in Guatemala (between 1977 and 1979) by Martorell et al. (1981). Also Pollet and Nettle (2008) observed that very short women in Guatemala more frequently give birth to a dead fetus, and therefore height is positively correlated with biological fitness of women in this population. Baqui et al. (1994) obtained similar results in Bangladesh. Additionally, height in women is known to correlate with other reproductive outcomes, for example, taller women’s babies tend to have higher birthweight (Kirchengast et al., 1998). What is more, a recent comparative study using Demographic and Health Survey data from 42 developing countries has also effectively demonstrated a positive relationship between maternal height and child survival that holds across varying levels of development in these countries (Monden and Smits, 2008), which is one of the most convincing comparative studies indicating a clear advantage for height, at least for women in high mortality populations. Human male height is associated with mate choice and intra-sexual competition, and therefore is only indirectly correlated with RS (Pawlowski et al., 2000). However, the results regarding males from native societies exhibit a considerable variation, sometimes even in the same study Kirchengast and Winkler (1995) observed that in Namibian Kavango males from Urban area of Rundu, and Kavango males from the rural areas around Rundu the relationship between height and RS was different. Generally, as summarized by Sear (2010), the findings regarding height and RS in both men and women should be interpreted with caution (also because they vary in terms of ages and control variables) and there seem to be no unambiguous conclusions. The discrepancies in these results suggest that the relationship between height and RS is heavily dependent on the environmental context (review: Sear, 2010). The present study tries to extend the generalizability of the previous results by conducting research in a native tribe of very limited contact with Western culture, the Yali (West Papua). In the context of the previously examined populations, this is a very specific and culturally different tribe, for example, because Yali men and women live separately (even if they are married), cohabiting only when they want to have a child. Since only a few accessible sources (Boissiere, 2002, 2009; Koch, 1974; Milliken, 1994; Sorokowski and Sorokowska, in press; Zoellner, 1988) have described the Yali and they are often very specific, describing only one, narrow problem, such as conflicts, agriculture, or beauty preferences, we present a detailed description of the Yali tribe, their economy and customs. 1.1. Yali population The research was conducted among the Yali tribe (Papua, semi-independent Indonesian province previously known as a Irian Jaya). The Yali inhabit the mountainous terrain east of the Baliem valley (3.92 S, 138.73 E for

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Wamena – central part of Baliem valley) known as Yalimo. It is a region of tropical climate. The Yali are one of many indigenous ethnic groups in West Papua. Because of difficult accessibility, Papua mountain terrains had not been explored until about 50 years ago (Koch, 1974; Milliken, 1994). The present study was conducted north of the summit of Mount Elit (also known as Gunung Elit; about 4000 m.a.s.l.) in a few small, isolated, mountain villages (e.g., Pui, Hiklahin, Ohomtongo, Sali, Fik-Fak, Mogobie, Penyam) and a larger village (Piliam). The villages were rarely visited by tourists (about 1–3 times in the last five years for small villages; 10–15 times a year for Piliam according to the inhabitants). Even though Christianity is present in this region, Yali have still preserved their traditional lifestyle including polygyny or clothing (some men wear only traditional koteka covering their penis; for information about koteka in other Papuan tribes see: Howard, 2000). Yali villages either have a doctor or are sometimes visited by a ‘‘mobile’’ nurse, traveling around the area, but none of the participants had access to any modern contraceptives. The Yali villages consist of one or more of the large men’s houses (yowa), and a cluster of smaller family huts (homea) (Boissiere, 2002). The men’s house is inhabited by all initiated males from the unit, and the house is a communal property. It has a ritual status, and uninitiated boys and females are not allowed inside. A family hut, constructed for a woman by her husband or sons, is where a married woman, her uninitiated sons and unmarried daughters live. Her own or her husband’s widowed or divorced mother might also live with her. In polygynous marriages the wives might share a household, but more frequently each of them has her own hut (Koch, 1974). After marriage, a woman lives in her husband’s village (personal observation by PS and AS). Yali are probably one of a few cultures such as Trobrianders and Marind Anim of Papua New Guinea (Oliver-Miller, 2004; Weiner, 1988) where men and women live separately (even if they are married). Yali inheritance rules are clearly defined and are described thoroughly by Koch (1974). They are very detailed and described inheritance practices in virtually all possible cases of someone’s death. Because of that as well as abundant land resources, and rather limited movable property of Yali, conflicts over property are infrequent. The tribe members’ sexual life is limited by certain traditional restrictions (taboos), both before and after the marriage. Girls and boys are discouraged from copulation before they reach sexual maturity. Boys are threatened that this might damage their vitality; most of girls are married before they have menarche but they are supposed to wait until they are ready to have children with their husband. However, pre-marital sexual intercourses also take place (personal observation). After marriage, a man should sleep in the men’s house at least every other night (otherwise he might be laughed at – Koch, 1974). Also, when a woman finds out that she is pregnant, the husband ceases to sleep in the family hut. Sexual intercourse should not take place for about four years after birth, so until the child is relatively independent (Koch, 1974). However, it is possible that some people do not comply with these rules (personal observation).

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1.2. Economy of Yali and the role of pigs Villages subsistence centers on horticulture. As described in detail by Koch (1974) and Milliken (1994), Yali practice shifting cultivation, relying primarily on sweet potato and taro as their staples. They also grow yams, pandanus, pitpit, sugar cane, bananas and a variety of leafy vegetables. Some crops, such as bananas, sugarcane, and cash crops (such as coffee and cocoa) are planted and tended by men. While women often help to pick the cash crops, most of the income goes to men. Men clear forests and bush, build houses and fences, while cultivation and harvesting are mainly done by the women. Also women do the daily cooking, while men butcher pigs for feasts. Men sometimes hunt for birds, bats and arboreal or terrestrial mammals found in the forest, such as tree kangaroos or giant rats. The only domesticated animals found everywhere are the pigs and the dogs (Koch, 1974). Children are also involved in subsistence of the household. Beginning from their first initiation, which happens when they are between eleven and thirteen, boys are gradually acquiring all the skills necessary to work individually. First they help their fathers and brothers, and later they cultivate plots by themselves. When boys are between seventeen and eighteen, they are thought to be sexually mature and ready for marriage (Koch, 1974). However, they do not usually marry before they are 20–25 years old (personal observation). Most girls have their first menarche relatively late – when they are between seventeen and nineteen (similarly to other tribes inhabiting New Guinea Highlands; Malcolm, 1966). At this age they are often married women (they get married between 15 and 19; personal observation). After menarche girls are thought to be able to pursue all the garden and housekeeping tasks (child-rearing, preparation of meals, tending the pigs, planting, weeding and harvesting) (Koch, 1974). Members of the other tribes have generally been considered as potential enemies: invaders or victims of aggression (for general situation in Papua see: Howard, 2000). Therefore, trade in Yalimo is limited to a few important goods and usually does not involve long-distance travelling. Small-scale trading takes place between Yali villages. Occasionally, some Yali cross the Gunung Elit to Wamena to sell some string bags or arrows at the city market. They also sell other items which are no longer available in the valley because of deforestation. Yali use the money to buy goods, however, they often use barter-like methods in trade. Salt or piglets, highly prized commodities, have often been traded in return for the goods sold by Yali (Matthiessen, 1989; Milliken, 1994). Presently Yali accept also money and use it to buy the tools and food accessible in Wamena shops (personal observation). Many previous studies have shown (e.g., Boyd, 1985; Kimber, 1972; Minnegal and Dwyer, 1997) that in the indigenous cultures of New Guinea, pigs carry significant social and cultural, as well as financial, value. All the abovementioned authors concordantly show that the number of possessed pigs is thought to have a significant effect on wealth and prestige in the cultures of the peoples who adopted it as their staple meat product (e.g., Kimber, 1972). In Papua New Guinea, pigs are even more valuable,

since they have a very slow growth rate there (because of lack of protein in the pig diet) – it commonly takes about 3–5 years to bring the pigs to maturity of 80–90 kg in Papua (compared with 4–5 months in Vietnam, for example) (Peters, 2002). Pigs in Yali tribe are used in purchases of more valuable commodities, wives (personal observation), and acquiring title to land (Koch, 1974). Apart from constituting a nutritional resource and a trade object, they are also used in social life. Virtually all social relationships have to be validated by pig exchanges. Also the settlements of bigger disputes or ratification of a peace agreement require the transfer of pigs (Koch, 1974). The same happens during all major events of a person’s life. For example, when someone dies, neighbors and relatives help the family to prepare the funeral and cremation. Although nobody expects any reward per se, the relative who is responsible for the cremation of the body must give a pig to the kinsman who carried the body to the pyre (a ‘‘corpse’’ pig). The recipient of the pig must return a ‘‘wood’’ pig (Koch, 1974). Also during a marriage, which is thought to be a union between two families, specially named pigs are exchanged. The husband gives ‘‘marriage’’ pigs to his wife’s family, and they give him the ‘‘dowry’’ pigs. The Yali word for the ‘‘marriage’’ pig signifies the ‘‘handing over’’ of a woman, and the dowry pig expresses ‘‘securing’’ the arrangement. The number of the exchanged pigs is not officially set, and depends on many factors. Exchanges of pigs and gifts continue throughout the marriage – although these are the sons, not the husband, who maintain such relationship with their mother’s family (Koch, 1974). It is also very interesting that although in the Yali tribe there is no official leadership, they have a term describing a man whose opinion is valued more than views of others. Such person is generally physically fit, eloquent and assertive, and – which is especially important for our topic – has a superior ability to provide pigs (for marriages, initiations, and situations when indemnity payments are necessary). In such a way, this person creates debt relationships with his relatives and neighbors. He may provide pigs either directly to his relatives or friends, or indirectly, by giving them the pigs for distribution among their families and friends. These contributions can give him ‘‘political’’ advantage (Koch, 1974), because people who owe him pigs are supposed to support him at all occasions. Koch (1974) wrote that ‘‘political status derives from the prestige he gains in his role as a pig broker’’ (p. 66). Therefore, we could summarize after Milliken (1994) that in the Yali tribe ‘‘man’s wealth is measured by the number of pigs and wives he possesses’’. 1.3. Aims of the study and hypotheses On the basis of presented theoretical background, the following hypotheses might be stated: Hypothesis 1. There exists a positive correlation between wealth (measured as the number of pigs), fertility, and number of children surviving until the reproductive age, and a negative correlation between wealth and child mortality in the Yali males/females.

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Hypothesis 2. Height of women should be negatively correlated with child mortality. It is hard to predict the relationship between female height and fertility. Similarly in males, such relationship is hard to predict, particularly because the previous study (Sorokowski and Sorokowska, in press) demonstrated that tall men are not preferred in that population. Based on the collected data, it is also possible to answer the following questions: Question 1. Does the higher number of children increase the child mortality in the Yali family? Negative correlation between family size and child survival have been successfully demonstrated in a few of contemporary African agriculturalist societies (review: Lawson and Mace, 2011) however the repeatability of such findings is not obvious (e.g., Borgerhoff Mulder, 1998). Question 2. Is height related to wealth in the Yali tribe? The previous studies conducted in Western societies demonstrated a strong correlation of this type (e.g., Frieze et al., 1990; Jackson and Ervin, 1992; Melamed, 1994), however the universality of such findings is not obvious. Godoy et al. (2010) have shown that among the Tsimane’, a native Amazonian society of foragers and farmers in Bolivia, adult height bore no significant association with, among others, income, or wealth.

2. Methods We tested 106 Yali participants of which 54 were female and 52 male. The female participants were aged between 19 and 50 years (M = 35.6, SD = 7.6) and male participants were aged between 25 and 59 years (M = 38.4, SD = 8.7). The age of each participant was self-estimated – majority of the participants did not know exactly how old they were. For this reason we did not ask about the age they got married – the question was too hard for majority of the participants. Although it is a polygynous society, only 25% of men had more than one wife. Descriptive statistics of the sample can be found in Table 1. All adults present in the villages at the time of the visit were invited to participate in the study. The participants were interviewed by Papuan assistant (from the Dani tribe) fluent in local dialects. Percentage of people who refused to participate was about 30–50%, depending on the village. The participants were asked how old they were, how many pigs their family had, how many children they have

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ever had (fertility), how many of them died. Men were also asked about the number of wives. The height of all the participants was measured by one of the authors (PS), experienced in such measurements. Height is considered an important variable as many previous studies demonstrated a relationship between height and various markers of reproductive success. All participants were reimbursed for their participation by receiving about 3USD. 3. Results 3.1. Fertility To assess the effects of ‘‘wealth’’ (here and thereafter: number of possessed pigs), ‘‘height’’ and ‘‘age’’ on ‘‘fertility’’ (number of all born children) standard multiple regression was used. The model was computed separately for men and women. Since the Yali tribe is polygynous, in the case of men, number of wives was additionally included into the regression model. Both for women and men, standard regression models were statistically significant (for women: adjusted R2 = .43, F(3,50) = 14.24, p < .0001; for men: adjusted R2 = .49, F(3,46) = 12.90, p < .0001). ‘‘Age’’ (for women: b = .60, t = 5.81, p < .0001; for men: b = .36, t = 3.30, p < .01), ‘‘wealth’’ (for women: b = .22, t = 2.09, p = .041; for men: b = .41, t = 3.94, p < .001) and, only for men, ‘‘number of wives’’ (b = .41, t = 3.88, p < .001) were significant predictors of ‘‘fertility’’, whereas ‘‘height’’ was a non-significant predictor of Yali fertility (for women: b = .16, t = 1.46, p = .15; for men: b = 0.05, t = 0.52, p = .60). A summary of the regression results is presented in Table 2. 3.2. Living children To assess the effects of ‘‘wealth’’, ‘‘height’’, ‘‘age’’ and ‘‘number of wives’’ (only for men) on the number of ‘‘living children’’ (or children surviving at least until reproductive age, which was defined as 14 years) standard multiple regression was used. The model was computed separately for men and women. Both models were statistically significant (for women: adjusted R2 = .38, F(3,50) = 12.02, p < .0001; for men: adjusted R2 = .55, F(4,46) = 16.33, p < .0001). Both for women and men, ‘‘age’’ (for women: b = .54, t = 4.97 p < .0001; for men: b = .38, t = 3.63, p < .001), ‘‘wealth’’ (for women: b = .27, t = 2.36 p = .02; for men: b = .42, t = 4.35, p < .0001) and, only for men, ‘‘number of wives’’ (b = .45, t = 4.52, p < .0001) were significant predictors of ‘‘number of living children’’. The

Table 1 Descriptive statistics of the Yali. Age Yali men (n = 52) Mean 38.4 SD 8.66 Yali women (n = 54) Mean 35.9 SD 7.62 a

Number of all children

Proportion [%] of dead childrena

Number of wives

Height [cm]

Number of pigs

3.9 2.48

15.0 17.82

1.3 .78

151.2 6.15

2.4 3.3

3.8 1.84

19.5 19.41

142.9 4.24

1.8 1.6

Only for participants with at least one child (females: n = 53, males: n = 49).

P. Sorokowski et al. / Economics and Human Biology 11 (2013) 382–390

386 Table 2 A summary of the regressions results. Fertility

,

Living children

2

Age Height ‘‘Wealth’’ TNOCHa <

Age Height ‘‘Wealth’’ No. of wives TNOCHa a

Children’s mortality

Adj. R = .43, F(3,50) = 14.24, p < .0001

Adj. R =. 38, F(3,50) = 12.02, p < .0001

Adj. R2 = .34, F(4,48) = 7.67, p<.0001

b

b

b

t

.60 .16 .23 –

p 5.81 1.46 2.09 –

<.0001 .15 .04

2

t .54 .18 .27

p 4.97 1.61 2.36

t

p

.07 .09 .13 .70

<.0001 .11 .02

.49 .76 1.05 4.64

.63 .45 .30 .0001

Fertility

Living children

Children’s mortality

Adj. R2 = .49, F(4,46) = 12.90, p < .0001

Adj. R2 = .55, F(4,46) = 16.33, p < .0001

Adj. R2 = .35, F(5,42) = 6.05, p < .001

b

t

p

b

b

.37 .05 .41 .41 –

3.30 .52 3.94 3.88 –

<.01 .60 <.001 <.001

t 0.38 0.04 0.42 0.45

p 3.63 0.40 4.35 4.53

<.001 .69 <.001 <.0001

t .18 .001 .22 .27 .84

p 1.33 .01 1.57 1.98 5.27

.19 .99 .12 .05 <.0001

Total number of children.

individual’s height did not predict the number of living children both for women (b = .18, t = 1.61, p = .11) and for men (b = .04, t = .40, p = .69). A summary of the regression results is presented in Table 2. 3.3. Child mortality To assess the effects of ‘‘wealth’’, ‘‘height’’, ‘‘age’’ and ‘‘number of wives’’ (only for men) on ‘‘child mortality’’, standard multiple regression was used. Additionally, we tested if the total number of children was related to the ‘‘child mortality’’. Therefore, ‘‘number of children’’ was added as another predictor. The model was computed separately for men and women. We excluded the participants without children (3 males and 1 female) from this analysis. Both models were statistically significant (for women: adjusted R2 = 34, F(4,48) = 7.67, p < .0001; for men: adjusted R2 = .35, F(5,42) = 6.05, p < .001), however, only one predictor i.e. the ‘‘total number of children’’ was significantly related to the ‘‘child mortality’’ (for women: b = .70, t = 4.64 p < .0001; for men: b = .84, t = 5.27, p < .0001). The ‘‘number of wives’’ (only for men) was marginally significant (b = .27, t = 1.98, p = .05). Other predictors such as ‘‘age’’ (for women: b = .07, t = .49 p = .63; for men: b = .18, t = 1.33, p = .19), ‘‘wealth’’ (for women: b = .13, t = 1.05 p = .30; for men: b = .22, t = 1.57, p = .12), ‘‘height’’ (for women: b = .09, t = .76 p = .45; for men: b = .001, t = .006, p = .99) did not relate to the ‘‘child mortality’’. A summary of the regression results is presented in Table 2. To test how exactly the number of children influenced ‘‘child mortality’’, we also interpreted unstandardized regression coefficient B. The analysis revealed that, for women, along with the increase of the total number of children by 1, the predicted number of children who died increased by B = .35 (SE = .08) similarly, a one unit increase in the total number of men’s children enlarged the predicted number of children who died by B = .3 (SE = .06).

Table 3 Additional comparisons (Mann–Whitney U-test) between currently monogamous and polygynous men.

Age Height No. of pigs

One wife (mean)

More than 1 wife (mean)

38.7 (n = 36) 150.1 (n = 35) 2.4 (n = 36)

39.8 (n = 13) 152.5 (n = 13) 2.8 (n = 13)

p

Z .45 1.17 .32

.65 .24 .75

3.4. Additional analyses In order to interpret the abovementioned analysis in greater details, we ran additional tests. Possible differences in ‘‘age’’, ‘‘height’’ and ‘‘wealth’’ between Yali men who had only one wife vs. those who had more than one wife were analyzed with a series of U Mann–Whitney tests. Both groups did not differ in terms of all three analyzed variables (Table 3). Additionally, body height was not correlated with the number of possessed pigs (for women: Spearman r = .22, n = 54, p = .11; for men: Spearman r = .04, n = 51, p = .78). 4. Discussion Our study extends the generalizability of the results of previous studies on the wealth-reproductive success relationship. Similarly to many pre-industrial human populations (historical and contemporary; e.g., Borgerhoff Mulder, 1987; Clarke and Low, 1992; Mace, 1996a; Skjærvø et al., 2011) in Yali tribe wealth covaried with reproductive success. Richer individuals, i.e. those who had more pigs had more children and higher reproductive success measured as the number of offspring that survive to reproductive age, i.e. 14 years of age. The obtained results highlight the importance of pigs in Papuan culture (Boyd, 1985; Kimber, 1972; Koch, 1974; Minnegal and Dwyer, 1997). We showed that the wealth measured in

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such a way might be related to the reproductive success of an individual. The ‘‘number-of pigs’’–RS relationship may be explained indirectly. Particularly, it is be possible that the differences in a diet of the wealthy and not-wealthy women, which, as it was shown in the previous studies, might strongly influence the fertility (Mabel, 2000), also in ‘‘native’’ populations (Marlowe, 2001; Wilmsen, 1982). Similarly, in Yali the ‘‘wealth’’ increased the total number of children and the number of living children. However it was not related to the ‘‘child mortality’’. This suggest that ‘‘wealth’’ or, more precisely, ‘‘lack of wealth’’ (in contrast to the poverty) may not be a cross-culturally universal negative factor limiting individual’s reproductive success. The observed extremely high child mortality in the harsh environmental conditions of Yalimo region came to almost 20% of children (81 out of 411) who did not survive until reproductive age. This result is comparable to the statistics in sub-Saharan Africa (e.g., Adjuik et al., 2006). However, contrary to the hypotheses, the ‘‘wealth’’ of participants did not influence the child mortality rate in Yali and this result differs from the outcomes obtained, for example, for developing, African countries (Anyamele, 2011). However, it might be possible that in Africa the wealthy individuals, contrary to poorer ones, have access to modern hospitals, better doctors, etc. At the same time, in Yali, even the relative wealth is not a guarantee of proper medical care (see Section 1). Our study also revealed that the individual’s body height in the Yali did not correlate with fertility, number of wives, number of living children or child mortality. The majority of conducted studies show that tall maternal height brings benefits in terms of better children survival, including populations in Gambia (Sear et al., 2004), Guatemala (Pollet and Nettle, 2008), and Bangladesh (Baqui et al., 1994). However, contradictory results have also been obtained – e.g., in a study conducted in Peru shorter women’s children had higher survival rate (Frisancho et al., 1973). In our study, neither paternal, nor maternal stature (which is even more surprising) correlated with child mortality. However in the Yali the relationship between the height and various reproductive measures may be diluted by the sexual taboos which introduce a few years period between possible attempts to have another child. No relationship between the total number of children and Yali stature is not, however, an unexpected result. Admittedly, it is different than previous outcomes in Western societies, which have shown that greater height among men but shorter among women can be linked to greater reproductive success (e.g., Mueller and Mazur, 2001; Nettle, 2002; Pawlowski et al., 2000). However, until now the results of studies conducted in populations of natural birth control have been highly inconclusive. For both women and men every possible relationship between height and number of children was obtained – positive, negative, non-linear and none at all (Sear, 2010). What is more, human male height is associated with reproductive success in the indirect context of mate choice and intrasexual competition, and recent studies indicate that preferences for taller men are not cross-culturally universal (Sear and Marlowe, 2009; Sorokowski et al., 2012). Also the

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study conducted among the Yali tribe (Sorokowski and Sorokowska, in press) suggests that the participants either do not have specific partner height preferences (in fact their choices were random) or that they are very diverse and equally divided between each possible combination of male and female stature (from a man being much taller than a woman to a woman being taller than a man). In any case, such preferences differed from several dozen previous studies showing strong ‘‘male-taller norm’’ in Western populations (e.g., Fink et al., 2007; Pawlowski, 2003). Therefore, no relationship between the height and number of children may be a relatively justified result. To verify the universality of the ‘‘male-taller norm’’ further studies should investigate if similar results would be obtained in different populations where tall stature may not be an advantage (for example, living in the jungle, like in the case of Yali people). In some environments, being shorter might facilitate hunting, climbing the trees or moving around. We also did not observe any relationship between the height and number of pigs in Yali population. On a contrary, in modern Western populations, the strong correlation between height and professional success was demonstrated in a number of studies (Sorokowski, 2010) and consequently it comes as no surprise that taller people appear to earn more (Frieze et al., 1990; Jackson and Ervin, 1992; Melamed, 1994). The positive height-wealth correlation was not a case in Yali. The described phenomenon may have its roots in the stereotypical view of personality traits and abilities of tall people. Numerous studies suggest that taller people are perceived as, for example, more talented and competent (Hensley and Cooper, 1987), more efficient (Kurtz, 1969), disciplined and with higher morale (Lester and Sheehan, 1980). As we concluded before, tall height might not be adaptive in a population living in environmental conditions like the Yali. In such case, the traits associated with being tall might be less positive, and consequently, taller people might be not preferred as partners (Sorokowski and Sorokowska, in press) and are not wealthier than shorter people, as we presented in this study. On the other hand, particularly in the developing countries, wealth might influence the height of people. It is known that childhood socioeconomic conditions influence stature in childhood and adulthood (Beard and Blaser, 2002; Bogin and MacVean, 1983; Leitch, 1951; Mitchell, 1962). The most important non-genetic factors affecting body height are nutrition and disease, both of which are socially patterned (Silventoinen, 2003). The influence of socioeconomic factors on height is so strong that it can be observed even on historical (Komlos et al., 2003; Steckel, 1995) or the country level of analyses (Batty et al., 2009; Komlos and Kriwy, 2002; Peck and Vagero, 1987). In such sense, the fact that wealthy Yali are not taller is puzzling. However, a similar outcome was obtained by Godoy et al. (2010) in the Tsimane. The authors discussed their results in the context of, among others, a ‘‘small-buthealthy’’ hypothesis (Seckler, 1982); it states that in many areas of low-income nations, being a short or stunted child (but not a wasted or a thin child) might be healthy and adaptive. However, this hypothesis is rather highly criticized (e.g., Beaton, 1989). Nevertheless, even if Seckler

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(1982) hypothesis is erroneous, our outcome and the results of Godoy et al. (2010) suggest that positive correlation between stature and wealth is not universal across populations and environmental conditions. Studies of a few native populations (Draper and Hames, 2000; Hill and Hurtado, 1996; Pennington and Harpending, 1988) showed strong positive correlation between fertility and number of grandchildren. However in the Dogon of Mali, Strassmann and Gillespie (2002) found that family size could have a negative effect on child survival rates. Additionally, traditional, indigenous populations might intend to maximize their reproductive success through planning the number of children (review: Lawson and Mace, 2011). For example, the decision to have another baby in Gabbra African tribes depends on household wealth and the number of children the family already has (Mace, 1996b). Strassmann (2000) showed that among Dogon of Mali, the chance of death of a child was 26% higher as the number of children (aged 10 years or under) increased by one. Since we also observed that the predicted number of children who died increased with the increase in the total number of children in family, we hypothesize that Yali’s families might limit their fertility to enhance survival rate of already born children. This suggestion corresponds with the Kaplan (1996) and Hrdy (1999) who showed that behavioural pathways of fertility regulation may often be institutionalized in social institutions and cultural practices, such as rules regulating marriage, inheritance, celibacy, contraception, infanticide and abandonment. The non-cohabiting of Yali population might be used to optimize the number of children depending on the family wealth. It might help the Yali babies to avoid starving (they do not have to share the food, such as mother’s milk, with siblings). It also helps the babies to survive – until they are about 4 years old they are constantly taken care of by their mother. Unfortunately, our data do not enable us to determine if such presumptions are true. We do not know if our participants actually ceased to cohabit every time the woman was pregnant and such variable can be controlled in the followup following studies. Our study has a few limitations. First of all, reproductive success should be measured in the long-term, and number of grandchildren would be helpful to determine that. Unfortunately, we did not collect such data during our research. Secondly, except for Skjærvø et al. (2011), the previous studies have not examined the possible local ecological impact on the association between status and reproductive success in humans. We also did not collect data about the ecology of visited villages (e.g., access to the plot, and meters above the sea level). However, in our opinion, they were not very significant. Nonetheless, further studies should include such variables in the analyses. Another variable we did not control was the sexual health of the female participants. Generally the level of sexually transmitted diseases (STDs) in West Papua is high (Simonin et al., 2011), which could definitely increase the infertility rate (Germain et al., 1992). We do not have detailed data regarding the Yali population, but according to our information, STDs are not a serious problem in this tribe.

Also, relatively high percentage of drop-out rates (30– 50%) could lead to a selection bias in our group. We hypothesize that the psychological variables (such as an interest in stranger visitors) determined the agreement to participate. However, it is also possible that poor people more likely took part in the survey, what could have lowered the average RS in our study. Finally, our data do ˜ o hurricane in 1997 not determine the effect the El Nin (Boissiere, 2002) had on the presented child mortality rates. All these limitations should be addressed in further studies of the Yali tribe. Acknowledgements We would like to thank the Editor, the anonymous reviewers and Anna Matysiak for their valuable comments and Aleksandra Gomuła for technical assistance in the preparation of this paper. Piotr Sorokowski was supported by a National Geographic scholarship (Polish ed.) and scholarship programme (2011–2014) funded by Polish Ministry of Science and Higher Education. References Adjuik, M., Smith, T., Clark, S., Todd, J., Garrib, A., Kinfu, Y., et al., 2006. Cause-specific mortality rates in sub-Saharan Africa and Bangladesh. Bulletin of the World Health Organization 84, 181–188. Anyamele, O.D., 2011. The role of wealth in infant mortality in subSaharan Africa within urban and between urban and rural areas. International Journal of Ecological Research 2, 73–81. Apicella, C.L., Feinberg, D.R., Marlowe, F.W., 2007. Voice pitch predicts reproductive success in male hunter-gatherers. Biology Letters 3, 682–684. Bailey, R., 1991. The Behavioral Ecology of Efe Pygmy Men in the Ituri Forest, Zaire. University of Michigan Museum of Anthropology, Ann Arbor. Baqui, A.H., Arifeen, S.E., Amin, S., Black, R.E., 1994. Levels and correlates of maternal nutritional-status in urban Bangladesh. European Journal of Clinical Nutrition 48, 349–357. Batty, G.D., Shipley, M.J., Gunnell, D., Huxley, R., Kivimaki, M., Woodward, M., et al., 2009. Height, wealth, and health: an overview with new data from three longitudinal studies. Economics and Human Biology 7, 137–152. Beard, A.S., Blaser, M.J., 2002. The ecology of height. Perspectives in Biology and Medicine 45, 475–498. Beaton, G.H., 1989. Small but healthy? Are we asking the right question?. Human Organization 48, 30–39. Bogin, B., MacVean, R.B., 1983. The relationship of socioeconomic status and sex to body size, skeletal maturation, and cognitive status of Guatemala City schoolchildren. Child Development 54, 115–128. Boissiere, M., 2002. The impact of drought and humanitarian aid on a Yali village on the West Papua, Indonesia. Asia Pacific Viewpoint 43, 293– 309. Boissiere, M., 2009. How does migration affect ethnobotanical knowledge and social organizations in a West Papuan village. In: Heckler, S. (Ed.), Landscapes, Process and Power. Berghan, pp. 183–204. Borgerhoff Mulder, M., 1987. On cultural and biological success: Kipsigis evidence. American Anthropologist 89, 619–634. Borgerhoff Mulder, M., 1998. Brothers and sisters. How sibling interactions affect optimal parental allocations. Human Nature 9, 119–162. Boyd, D.J., 1985. We must follow the Fore: pig husbandry intensification and ritual diffusion among the Irakia Awa, Papua New Guinea. American Ethnologist 12, 119–136. Casimir, M., Rao, A., 1995. Prestige, possessions and progeny: cultural goals and reproductive success among the Bakkarwal. Human Nature 6, 241–272. Clarke, A.L., Low, B.S., 1992. Ecological correlates of human dispersal in 19th-century Sweden. Animal Behaviour 44, 677–693. Cronk, L., 1991. Wealth, status and reproductive success among the Mukogodo of Kenya. American Anthropologist 93, 345–360. Daly, M., Wilson, M., 1983. Sex, Evolution, and Behavior. Duxbury Press, Boston.

P. Sorokowski et al. / Economics and Human Biology 11 (2013) 382–390 Devi, M.R., Kumari, J.R., Srikumari, C.R., 1985. Fertility and mortality differences in relation to maternal body size. Annals of Human Biology 12, 479–484. Draper, P., Hames, R., 2000. Birth order, sibling investment, and fertility among Ju/’Hoansi (!Kung) Human Nature 11, 116–156. Dribe, M., 2004. Long-term effects of childbearing on mortality: evidence from pre-industrial Sweden. Population Studies: A Journal of Demography 58, 297–310. Fielding, R., Schooling, C.M., Adab, P., Cheng, K.K., Lao, X.Q., Jiang, C.Q., Lam, T.H., 2008. Are longer legs associated with enhanced fertility in Chinese women? Evolution and Human Behavior 29, 434–443. Fink, B., Neave, N., Brewer, G., Pawlowski, B., 2007. Variable preferences for sexual dimorphism in stature (SDS): further evidence for an adjustment in relation to own height. Personality and Individual Differences 43, 2249–2257. Fisher, R.A., 1930. The Genetical Theory of Natural Selection. Clarendon Press, Oxford. Flinn, M., 1986. Correlates of reproductive success in a Caribbean village. Human Ecology 14, 225–243. Frieze, I.H., Olson, J.E., Good, D.C., 1990. Perceived and actual discrimination in the salaries of male and female managers. Journal of Applied Social Psychology 20, 46–67. Frisancho, A.R., Sanchez, J., Pallarde, D., Yanez, L., 1973. Adaptive significance of small body size under poor socioeconomic conditions in Southern Peru. American Journal of Physical Anthropology 39, 255– 261. Germain, A., Holmes, K.K., Piot, P., Wasserheit, J.N., 1992. Reproductive Tract Infections: Global Impact and Priorities for Women’s Reproductive Health. Plenum Press, New York. Godoy, R.A., Magvanjav, O., Nyberg, C., Eisenberg, D.T.A., McDade, T.W., Leonard, W.R., et al., 2010. Why no adults stunting penalty or height premium? Estimates from native Amazonians in Bolivia. Economics and Human Biology 8, 88–89. Hensley, W.E., Cooper, R., 1987. Height and occupational success: a review and critique. Psychological Reports 60, 843–849. Hill, K., Hurtado, A.M., 1996. Ache Life History: The Ecology and Demography of a Foraging People. Aldine de Gruyter, New York, NY. Hopcroft, R.L., 2006. Sex, status, and reproductive success in the contemporary United States. Evolution and Human Behavior 27, 104– 120. Howard, M.C., 2000. Dress and ethnic identity in Irian Jaya. Journal of Social Issues in Southeast Asia 15, 1–29. Hrdy, S.B., 1999. Mother Nature: A History of Mothers, Infants and Natural Selection. Pantheon, New York, NY. Irons, W., 1979. Cultural and biological success. In: Chagnon, N., Irons, W. (Eds.), Evolutionary Biology and Human Social Behavior: An Anthropological Perspective. North Sci., Duxbury Press, pp. 257–272. Jackson, L.A., Ervin, K.S., 1992. Height stereotypes of women and men: the liabilities of shortness for both sexes. Journal of Social Psychology 132, 433–445. Kaplan, H., 1996. A theory of fertility and parental investment in traditional and modern human societies. Yearbook of Physical Anthropology 39, 91–135. Kimber, A.J., 1972. The sweet potato in subsistence agriculture. Papua New Guinea Agricultural Journal 23, 80–95. Kirchengast, S., 2000. Differential reproductive success and body size in !Kung San people from Northern Namibia Collegium Antropollogicum 24, 121–132. Kirchengast, S., Hartmann, B., Schweppe, K.W., Husslein, P., 1998. Impact of maternal body build characteristics on newborn size in two different European populations. Human Biology 70, 761–774. Kirchengast, S., Winkler, E.M., 1995. Differential reproductive success and body dimensions in Kavango males from urban and rural areas in Northern Namibia. Human Biology 67, 291–309. Koch, K.F., 1974. War and Peace in Jalemo. The Management of Conflict in Highland New Guinea. Harvard University Press, Cambridge, MA. Komlos, J., Hau, M., Bourginat, N., 2003. An anthropometric history of early-modern France. European Review of Economic History 7, 159– 189. Komlos, J., Kriwy, P., 2002. Social status and adult heights in the two Germanies. Annals of Human Biology 29, 641–648. Kurtz, D.L., 1969. Physical appearance and stature: important variables in sales recruiting. Personnel Journal 48, 981–983. Lawson, D.W., Mace, R., 2011. Parental investment and the optimization of human family size. Philosophical Transactions of the Royal Society B 366, 333–343. Leitch, I., 1951. Growth and health. British Journal of Nutrition 5, 142– 151. Lester, D., Sheehan, D., 1980. Attitudes of supervisor toward short police officers. Psychological Reports 47, 462.

389

Lycett, J.E., Dunbar, R.I.M., Voland, E., 2000. Longevity and the costs of reproduction in a historical human population. Proceedings of the Royal Society B 267, 31–33. Mabel, B., 2000. Diet and fertility. Nutrition and Food Science 30, 109– 111. Mace, R., 1996a. Biased parental investment and reproductive success in Gabbra pastoralists. Behavioral Ecology and Sociobiology 38, 75–81. Mace, R., 1996b. When to have another baby: a dynamic model of reproductive decision-making and evidence from Gabbra pastoralists. Ethology and Sociobiology 17, 263–273. Malcolm, L.A., 1966. The age of puberty in the Bundi People. Papua and New Guinea Medical Journal 9, 16–20. Marlowe, F., 2001. Male contribution to diet and female reproductive success among foragers. Current Anthropology 42, 755–760. Martorell, R., Delgado, H.L., Valverde, V., Klein, R.E., 1981. Maternal stature, fertility and infant mortality. Human Biology 53, 303–312. Matthiessen, P., 1989. Under the Mountain Wall. A Chronicle of Two Seasons in Stone Age. Collins Harvill, New Guinea/London. Melamed, T., 1994. Correlates of physical features: some gender differences. Personality and Individual Differences 17, 689–691. Milliken, W., 1994. Ethnobotany of the Yali of West Papua. Royal Botanic Garden, Edinburgh. Minnegal, M., Dwyer, P.D., 1997. Women, pigs, God and evolution: social and economic change among Kubo people of Papua New Guinea. Oceania 68, 47–60. Mitchell, H.S., 1962. Nutrition in relation to stature. Journal of American Dietetic Association 40, 521–524. Monden, C.W.S., Smits, J., 2008. Maternal height and child mortality in 42 developing countries. American Journal of Human Biology 21, 305–311. Mueller, U., Mazur, A., 2001. Evidence of unconstrained directional selection for male tallness. Behavioral Ecology and Sociobiology 50, 302– 311. Nettle, D., 2002. Women’s height, reproductive success and the evolution of sexual dimorphism in modern humans. Proceedings of the Royal Society B 269, 1919–2192. Oliver-Miller, S., 2004. Papua New Guinea. In: Francoeur, R.T., Noonan, R.J. (Eds.), International Encyclopedia of Sexuality. Continuum, New York. Pawlowski, B., 2003. Variable preferences for sexual dimorphism in height as a strategy for increasing the pool of potential partners in humans. Proceedings of the Royal Society B 270, 709–771. Pawlowski, B., Dunbar, R., Lipowicz, A., 2000. Tall men have more reproductive success. Nature 403, 156. Peck, A.M., Vagero, D.H., 1987. Adult body height and childhood socioeconomic group in the Swedish population. Journal of Epidemiology and Community Health 41, 333–337. Pennington, R., Harpending, H., 1988. Fitness and fertility among Kalahari !Kung American Journal of Physical Anthropology 77, 303–319. Peters, D., 2002. Poverty alleviation and food security through improving human–pig–sweet potato systems in Papua, Indonesia. Paper presented in CIP-Indonesia Research Review Workshop, Bogor, Indonesia, March 26–27, 2002. Pettay, J.E., Helle, S., Jokela, J., Lummaa, V., 2007. Natural selection on female life-history traits in relation to socio-economic class in preindustrial human populations. PLoS ONE 2 (7), e606. Pollet, T.V., Nettle, D., 2008. Taller women do better in a stressed environment: height and reproductive success in rural Guatemalan women. American Journal of Human Biology 20, 264–269. Røskaft, E., Wara, A.L., Viken, A˚., 1992. Reproductive success in relation to resource-access and parental age in a small Norwegian farming parish during the period 1700–1900. Ethology and Sociobiology 13, 443–461. Sear, R., 2010. Height and reproductive success: is bigger always better? In: Ulrich, F., Stoermer, C., Willfuehr, K. (Eds.), Homo Novus: A Human Without Illusions. Springer, Berlin, Heidelberg, pp. 127–143. Sear, R., Allal, N., Mace, R., 2004. Height, marriage and reproductive success in Gambian women. Research in Economic Anthropology 23, 203–224. Sear, R., Marlowe, F.W., 2009. How universal are human mate choices? Size does not matter when Hadza foragers are choosing a mate. Biology Letters 5, 606–609. Seckler, D., 1982. Small but healthy: a basic hypothesis in the theory, measurement and policy of malnutrition. In: Sukhatme, P.V. (Ed.), Newer Concepts in Nutrition and their Implications for Policy. Maharashtra Association for the Cultivation of Science Research Institute, Pune, India, pp. 127–137. Silventoinen, K., 2003. Determinants of variation in adult body height. Journal of Biosocial Science 35, 263–285. Simonin, A., Bushee, J., Courcaud, A., 2011. Social, cultural and political factors in the design of HIV programmes with Papuan highland communities. Culture, Health and Sexuality 13, 185–199.

390

P. Sorokowski et al. / Economics and Human Biology 11 (2013) 382–390

Steckel, R.H., 1995. Stature and the standard of living. Journal of Economic Literature 33, 1903–1940. Skjærvø, G.R., Bongard, T., Viken, A˚., Stokke, B.G., Røskaft, E., 2011. Wealth, status, and fitness: a historical study of Norwegians in variable environments. Evolution and Human Behavior 32, 305–314. Smith, E.A., 2004. Why do good hunters have higher reproductive success? Human Nature 15, 343–364. Sorokowski, P., 2010. Politicians’ estimated height as an indicator of their popularity. European Journal of Social Psychology 40, 1302–1309. Sorokowski, P., Sorokowska, A. Judgments of sexual attractiveness: a study of the Yali tribe in Papua. Archives of Sexual Behavior, in press, doi:10.1007/s10508-012-9906-x. Sorokowski, P., Sorokowska, A., Fink, B., Mberira, M., 2012. Variable preferences for sexual dimorphism in stature (SDS) might not be universal: data from a semi nomad population (Himba) in Namibia. Journal of Cross-Cultural Psychology 43, 32–37. Strassmann, B., 1997. Polygyny is a risk factor for child mortality among the Dogon. Current Anthropology 38, 688–695. Strassmann, B., 2000. Polygyny, family structure and child mortality: a prospective study among the Dogon of Mali. In: Cronk, L., Chagnon,

N., Irons, W. (Eds.), Adaptation and Human Behavior: An Anthropological Perspective. Aldine de Gruyter, New York, pp. 49–67. Strassmann, B., Gillespie, B., 2002. Life-history theory, fertility and reproductive success in human. Proceedings of Royal Society B Biological Sciences 269, 553–562. Trivers, R.L., 1972. Parental investment and sexual selection. In: Campbell, B. (Ed.), Sexual Selection and the Descent of Man. Aldine, Chicago, pp. 1871–1971. Turke, P., Betzig, L., 1985. Those who can do: wealth status and reproductive success on Ifaluk. Ethology and Sociobiology 6, 79–87. Weiner, A.B., 1988. The Trobrianders of Papua New Guinea. Holt, Rinehart and Winston, New York. Wilmsen, E.N., 1982. Studies in diet, nutrition, and fertility among a group of Kalahari Bushmen in Botswana. Social Science Information 21, 95– 125. Wilson, E.O., 1975. Sociobiology. Harvard University Press, Cambridge, MA. Zoellner, S., 1988. The Religion of the Yali in the Highlands of Irian Jaya. Melanesian Institute for Pastoral and Socio-economic Service, Goroka.