Who teaches children to forage among Hadza and BaYaka Hunter-Gatherers of Tanzania and Congo? Child-to-child teaching was more frequent than adult-child teaching; and children taught more with age

Who teaches children to forage? Exploring the primacy of child-to-child teaching among Hadza and BaYaka Hunter-Gatherers of Tanzania and Congo. Sheina Lew-Levy et al. Evolution and Human Behavior, Volume 41, Issue 1, January 2020, Pages 12-22. https://doi.org/10.1016/j.evolhumbehav.2019.07.003

Abstract: Teaching is cross-culturally widespread but few studies have considered children as teachers as well as learners. This is surprising, since forager children spend much of their time playing and foraging in child-only groups, and thus, have access to many potential child teachers. Using the Social Relations Model, we examined the prevalence of child-to-child teaching using focal follow data from 35 Hadza and 38 BaYaka 3- to 18-year-olds. We investigated the effect of age, sex and kinship on the teaching of subsistence skills. We found that child-to-child teaching was more frequent than adult-child teaching. Additionally, children taught more with age, teaching was more likely to occur within same-sex versus opposite-sex dyads, and close kin were more likely to teach than non-kin. The Hadza and BaYaka also showed distinct learning patterns; teaching was more likely to occur between sibling dyads among the Hadza than among the BaYaka, and a multistage learning model where younger children learn from peers, and older children from adults, was evident for the BaYaka, but not for the Hadza. We attribute these differences to subsistence and settlement patterns. These findings highlight the role of children in the intergenerational transmission of subsistence skills.

6. Discussion

The present study aimed to investigate how age, sex, and kinship influenced the teaching of subsistence skills in BaYaka and Hadza forager 3- to 18-year-olds. Our findings suggest that Hadza and BaYaka children participated in teaching, either as a teacher or as a learner, between 6 and 8 times an hour. A majority of these teaching events occurred within child dyads. Alongside research among the Aka and Ngandu (Boyette & Hewlett, 2017a; Hewlett & Roulette, 2016), Baka (Gallois, Duda, Hewlett, & Reyes-garcía, 2015), Maya (Maynard, 2002; Zarger, 2002), and Fijians (Kline, 2016), our results highlight the central role Hadza and BaYaka children play as teachers, and not just acquirers, of cultural knowledge.

Children in both populations taught more with age, with overall teaching directed to children peaking in adulthood. Teaching likely develops with age because children's teaching abilities continue to increase, and because they have more knowledge to share with others (Strauss & Ziv, 2012). Though the development of children's teaching abilities have been documented in multiple societies in the industrialized west (see Strauss & Ziv, 2012 for review), our findings lend support to a growing body of evidence demonstrating that in non-western societies, this development occurs independently of intensive formal schooling (Boyette & Hewlett, 2017a; Maynard & Tovote, 2009). Interestingly, after approximately 30, the teaching of children actually decreased with age. Since, by 30, most adults have children who are old enough to teach their younger siblings, our findings may reflect children's participation in offsetting their cost of care. Children's participation in economic activities among the Maya likely increases mother's reproductive success (Lee & Kramer, 2002). By accelerating other children's subsistence knowledge acquisition through teaching, children may be increasing their inclusive fitness by promoting sibling self-sufficiency and shortening parental inter-birth interval. Children may also be improving their individual fitness by increasing their share of parental provisioning. Furthermore, children may liberate parents to teach more complex skills to adolescents and other adults, thus reducing the cost of cumulative cultural transmission.

Consistent with kin selection theory, teaching was more likely to occur between related dyads than unrelated dyads in both groups. However, when compared to non-kin and other-kin, sibling teaching was more common among the Hadza than among the BaYaka. We interpret these findings as indicating that teaching was more likely to occur within nuclear families among the Hadza compared to the BaYaka. We propose that these findings are related to camp structure. As noted earlier, BaYaka camps are typically more compact than Hadza camps (Hewlett et al., 2019) partially because of the constraints imposed by living in a forested environment rather than in the savannah. As a result, BaYaka children are invariably in closer proximity to all other camp members while in camp, while Hadza children can more easily assort with more closely related individuals, including siblings and parents. This may result in different teaching patterns, where other-kin and non-kin play a greater role in knowledge transmission for the BaYaka, whereas for the Hadza, the nuclear family may play a greater role in knowledge transmission. An alternative explanation may be simply that, because the Hadza have more siblings than the BaYaka, the former experienced more sibling teaching than the latter. However, Blurton Jones (2016) states that the total fertility rate for the Hadza is 5.3, while, for the BaYaka, total fertility rate is reported by Hewlett (1991) as 6.2, with similar infant mortality rates (~20% Blurton Jones, Hawkes, & O'Connell, 2002; Hewlett, 1991). Furthermore, as Table 1 shows, the BaYaka had proportionally more siblings in camp than the Hadza (5% vs. 3%), making it unlikely that number of siblings in camp explains the observed difference in Hadza and BaYaka sibling teaching. Thus, our results suggest that intra-site variation in settlement structure may influence the distribution of kin teaching. Future studies should further investigate this claim.

For the BaYaka only, younger children were more likely to be taught by other children while BaYaka adolescents were more likely to be taught by adults. This finding is consistent with the multistage model of knowledge acquisition, which suggests that children develop basic skills from other children before seeking skilled adults from whom they can update their knowledge, and who might also be more willing to teach individuals with the necessary baseline competence (Henrich & Henrich, 2010; Reyes-García et al., 2016). While our data support a multistage model of learning among the BaYaka, we found little difference in teacher's age for younger and older learners among the Hadza. While unexpected, this finding may be explained by examining foraging participation. Hadza children collect between 25 and 50% and sometimes even 100% of their daily caloric needs from an early age (Crittenden et al., 2013; Hawkes et al., 1995). Although children tend to target easier to access resources such as berries and baobab when they are younger, they are provided with opportunities to practice more complex resource acquisition throughout childhood; for example, boys as young as two are made small, functional bows and arrows, and girls are provided with small, appropriately sized digging sticks (Crittenden, 2016). Unlike among the BaYaka, children are fully expected to collect food with these tools. Thus, for the Hadza, teaching by adults may primarily occur through stimulus enhancement in early life, after which children are more likely to learn complex skills through participation in foraging with other children than through teaching by adults. Though a multistage learning model where children learn with other children when younger, and by adults when older may be more common, it may nonetheless depend on the foraging niche in which learning occurs. Future studies should thus take seriously the role of ecological context when investigating the distribution of learning processes across the lifespan.

Mathematical models investigating optimal learning strategies suggest that individual learning should occur only after children have acquired knowledge socially (Aoki, Wakano, & Lehmann, 2012; Borenstein, Feldman, & Aoki, 2008; Lehmann et al., 2013). Although previous studies of play (Bock & Johnson, 2004), observation (Greenfield, 2004), and teaching (Boyette & Hewlett, 2017a) found that social learning declined with age, presumably because older individuals have begun to refine learned behavior through individual practice, our final model found only a weak negative relationship between learner's age and teaching. However, we note that learner's age was a strong negative predictor in additional models which omitted this interaction (see supplementary materials). This suggests that what might first appear to be a decreasing likelihood for older individuals to be learners is actually better explained by (a) a decrease in teaching by older individuals, due to the declining latter portion of the quadratic ‘teacher age’ curve (Fig. 1), and (b) a tendency for teachers and learners to be of similar ages, as indicated by the positive teacher/learner age interactions. In other words, the decline in teaching by older individuals is sufficient to explain the decline in learning by older individuals as well.

As in other aspects of forager life (Allen-Arave et al., 2008; Crittenden & Zes, 2015; Peterson, 1993), we found evidence for high dyadic reciprocity, and a large effect of the dyad, in teaching. Researchers working with highly stratified cultures have found collaboration to enhance children's knowledge acquisition in experimental settings (Dean, Kendal, Schapiro, Thierry, & Laland, 2012; Dunn, 1983; Laland, 2004; Tomasello, 1999; Tomasello et al., 1993; Wood, Wood, Ainsworth, & Malley, 1995). When comparing collaborative problem solving across cultures, Nielsen, Mushin, Tomaselli, and Whiten (2016) found that Australian Indigenous children collaborated significantly more than Brisbane pre-schoolers (see also Rogoff, 1998). Since collaborative learning generates new knowledge forms (Tomasello, 1999; Tomasello et al., 1993), it may be especially adaptive to foragers relying on unpredictable resources. One limitation of our study is that we examined short-term reciprocity. A long term examination of teaching may show a different, and more unidirectional, pattern. Nonetheless, future studies should examine the advantages conferred by reciprocal knowledge sharing during daily interactions in childhood.

Finally, same-sex teaching was hypothesized to increase the likelihood that children would learn sex-specific skills (Henrich & Gil-White, 2001). Same-sex bias in learning has been noted among foragers the world over (Boyette & Hewlett, 2017a; Draper, 1975; Hewlett & Cavalli-Sforza, 1986; Lew-Levy, Lavi, Reckin, Cristóbal-Azkarate, & Ellis-Davies, 2018; MacDonald, 2007b). Here, we also found strong evidence for same-sex teaching among both the BaYaka and the Hadza.

7. Implications

Taken together, this paper sheds light on the evolutionary importance of, and cross-cultural variation in, child-to-child teaching. Most studies investigating the evolution of childhood have assumed that children require provisioning until at least adolescence (Kaplan et al., 2000), yet recent studies have challenged this claim, showing that children can be, and often are, producers (Bird & Bliege Bird, 2005; Crittenden et al., 2013; Tucker & Young, 2005), that children sometimes produce a surplus of calories which can be shared with the parental generation (Crittenden et al., 2013), and that children's production contributes to parental reproduction (Kramer, 2014; Lee & Kramer, 2002). Similarly, many studies on the evolution of cumulative culture assume that transmission only or primarily occurs from parents to offspring (e.g. Shennan & Steele, 1999), and that childhood is a sensitive period for knowledge acquisition (Kaplan et al., 2000). The results of the present paper problematize these claims because they demonstrate that children are active teachers from an early age. Child-to-child teaching may be especially adaptive because it has the potential to increase children's inclusive and individual fitness by offsetting their own, and their siblings' cost of care (Konner, 1976; Lee & Kramer, 2002). Furthermore, because children can facilitate each other's knowledge acquisition in the zone of proximal development, child-to-child teaching may contribute to more rapid, and potentially less costly, knowledge transfers for basic skills (Hewlett & Cavalli-Sforza, 1986).

Our analysis was limited by the fact that dyadic proximity data proved too difficult to collect while also keeping track of children's teaching and foraging activities. Dyadic proximity is important because individuals may choose to assort with the intent to share knowledge with each other. At least among the BaYaka, adults report inviting children to forage alongside them with the specific intent to teach subsistence skills (Lew-Levy et al., 2019). Similarly, BaYaka children sometimes preferred to forage in the absence of adults so that they could learn with their peers (Boyette & Lew-Levy, Under review). Alternatively, teaching may occur opportunistically while individuals are participating in other cooperative behaviors. For example, parents who forage with their children because they require assistants may also use a foraging trip as an opportunity to teach. Thus, future studies should examine whether teaching is independent from, or a by-product of, other social and cooperative relationships. Future studies should also examine whether cross-cultural differences in associative patterns translates to differences in teaching.

The present paper brings to light several areas for future research. Since fieldwork was only conducted during part of the year, we were unable to observe every foraging activity (e.g. kombi fishing for the BaYaka, weaver-bird collecting for the Hadza); future studies will examine how seasonal variation in child and adult foraging and diet influences how and from whom children learn (Crittenden & Schnorr, 2017; Gallois et al., 2015). In addition, as demonstrated in Table S3, we observed little teaching in especially complex domains, such as hunting and trapping. This may be because these skills are acquired later in life (Gurven, Kaplan, & Gutierrez, 2006; Ohtsuka, 1989; Walker et al., 2002). Since the age cut-off for the present study was approximately eighteen, more longitudinal studies on the distribution of knowledge acquisition across seasons, and in late adolescence and adulthood are needed. Studies comparing teaching to other social learning forms, such as observation and imitation, are also needed. Next, while the present paper considered teaching generally, future studies will examine whether different teaching types covary with the specific domain of subsistence being transmitted. Finally, the foragers with whom we worked had limited exposure to schooling. Future studies will examine how teaching patterns change with increased exposure to schools.