Information transmission and the oral tradition: Evidence of a late-life service niche for Tsimane Amerindians

Abstract

Storytelling can affect wellbeing and fitness by transmitting information and reinforcing cultural codes of conduct. Despite their potential importance, the development and timing of storytelling skills, and the transmission of story knowledge have received minimal attention in studies of subsistence societies that more often focus on food production skills. Here we examine how storytelling and patterns of information transmission among Tsimane forager-horticulturalists are predicted by the changing age profiles of storytellers’ abilities and accumulated experience. We find that storytelling skills are most developed among older adults who demonstrate superior knowledge of traditional stories and who report telling stories most. We find that the important information transmitted via storytelling typically flows from older to younger generations, and stories are primarily learned from older same-sex relatives, especially grandparents. Our findings suggest that the oral tradition provides a specialized late-life service niche for Tsimane adults who have accumulated important experience and knowledge relevant to foraging and sociality, but have lost comparative advantage in other productive domains. These findings may help extend our understanding of the evolved human life history by illustrating how changes in embodied capital predict the development of information transmission services in a forager-horticulturalist economy.

Introduction

Before written language, mass printing, and electronic broadcast, cumulative traditional ecological knowledge (TEK) “about the relation of living beings (including humans) with one another and with their environment” was largely transmitted across generations using oral traditions (Berkes, Colding, & Folke, 2000: 1252). Across cultures, storytelling and music continue to play central roles in traditional education (Scalise Sugiyama, 2001). Stories and songs often encode fitness-relevant information about hazards, subsistence, morality, mythology, norms, marriage and relationships (Scalise Sugiyama, 1996). For example, most human subsistence skills require cumulative knowledge that is often transmitted from older to younger generations. Without effective information transmission, complex skill development using only individual learning and effort would be very difficult or impossible (Boyd & Richerson, 1985). Skilled communicators in the oral tradition can make difficult-to-acquire information salient, memorable, and amenable to re-transmission, helping individuals develop the complex skills they will need in adulthood (Rubin, 1997). Stories also provide listeners opportunity to engage in low-cost “cognitive play” as they imagine beliefs and desires of other minds, and simulate problems (Boyd, 2009). For example, traditional stories often feature solutions to unpredictable or rare events and potentially deadly problems (e.g. natural hazards, predators, adversarial conspecifics) that are of great importance but can be costly to discover through first-hand experience (Coe et al., 2005a, Coe and Palmer, 2008). Independent of information value, stories and music are entertaining – providing a social lubricant among kin that can reinforce ties, mitigate conflicts, and improve gains from cooperation (Boyd, 2009, Coe and Palmer, 2008, Steadman and Palmer, 1997).

Social and ecological context may affect who tells stories and performs music and who learns from performances. Ethnographic accounts of subsistence societies often portray skilled storytellers and musicians as older adults or grandparents (e.g. Biesele, 1993, Hallowell, 1992, Simmons, 1945). Describing Yakutat Tlingit hunter-gatherers, de Laguna (1997, p.839) writes, “when an informant indicated how he or she had learned myth or legend it was from a grandmother or grandfather, less often from a father or mother”. Though only a small percentage of the population, these “active bearers” are responsible for maintaining the oral tradition by intergenerational transmission (Acerbi et al., 2017, Coe and Palmer, 2008). While storytellers and musicians from traditional societies have been characterized as mostly older specialists (Archibald, 2008, Hale, 1998), little empirical evidence is available to support claims that oral tradition is learned from the oldest generations.

Much of what is known about narrative and musical skill development concerns economically advanced society, where a different pattern is described: according to Miller (1999), peak ages for popular music production (females 29, males 33 for rock; females 39, males 30 for jazz) and literature (females 50, males 43) coincide more with reproductive and parenting ages. Economically advanced society offers young adults more specialized career path options, while most people of the same age and sex have the same common skills and do the same work in traditional subsistence society. By performing a large repertoire of stories and songs in ways that lower-fitness competitors cannot, storytelling and music specialists can broadcast honest signals (e.g. of intelligence and experience, sensu Miller, 2011) that might attract mates and allies. Economically advanced societies are also faced with rapidly changing problem sets (i.e., each generation faces many novel problems previous generations did not) that are better served by novel cultural solutions. Cultural evolution theory (e.g. Boyd & Richerson, 1985) suggests that horizontal (learning from peers) transmission will be preferred where a premium is placed on new solutions; suggesting that the role of culture transmitter in economically advanced society need not be restricted to older adults.

Here we examine the life course trajectory of skill development in the Tsimane oral tradition and patterns of information transmission attributed to this developmental process. We consider whether Tsimane storytelling is better understood as a common or specialized skill. Schniter, Gurven, Kaplan, Wilcox, and Hooper (2015) showed that most traditional Tsimane skills are developed by most adults. As a common skill, we would expect storytelling to be developed by most adults and to be positively associated with ability and expertise across other common skills and forms of productivity. As a specialized skill, storytelling is only undertaken by those who are at a comparative advantage to do so, and who otherwise may be losing fitness-enhancing value to co-resident kin due to senescence-related declines in other domains of productivity (e.g. hunting, farming, food processing). Whether older adults are expert storytellers because of the long learning curve which they share with all others their age, or because they represent the select few in their age cohort who can realize a competitive advantage in the oral tradition over other skill domains, is of direct relevance to the idea of longevity evolving with selection against post-reproductive cognitive decline due to the value of older adults' accumulative knowledge (e.g. Schwarz et al., 2016).”

Among Tsimane forager-horticulturalists of Bolivia, the oral tradition has long served as a form of enjoyable cultural education tied to the important tradition of sobaqui, visitation with kin, neighbors and friends (Ellis, 1996). Tsimane storytelling occurs most often when it creates the fewest opportunity costs for transmitters and receivers: when people get together to visit, especially at small fireside family gatherings (de la De La Quintana & Daillant, 1999).¹ Prior to the introduction of formal schools and radios in the second half of the 20th century, the role of educator and entertainer fell on local experts, including cocojsi or shamans. Shamans have almost entirely disappeared from Tsimane culture. However, when vats of shocdye—a homebrewed manioc beer—are available, family and neighbors gather to drink communally. At family and community gatherings, older adults broadcast their knowledge by conveying details about memorable hunting trips, telling personal and traditional stories, interpreting dreams, and with jimacdye—instrumental music and song (Ellis, 1996, Iamele, 2001, Schniter, 2014). We further explain facets of Tsimane oral tradition in Section 1.1.

We consider how informants' age, story knowledge, abilities, and available audiences affect patterns of information transmission across the lifespan in a small-scale forager-horticulturalist society. Embodied Capital Theory (ECT) proposes that several unique features of the human life course are adapted responses to a skills-intensive, socio-ecological niche (Kaplan, Gurven, Winking, Hooper, & Stieglitz, 2010). Specifically, ECT hypothesizes that the life course of skill performance is shaped by characteristics of specific tasks (i.e. their difficulty, strength, motor dexterity, and knowledge requirements), the changing capabilities of individuals with age and experience, and the changing needs of the family budget (Bock, 2002a, Bock, 2002b, Crittenden et al., 2013, Gurven and Kaplan, 2006, Schniter et al., 2015). As adults become grandparents and advance through their post-reproductive years, physical declines in strength, endurance, and manual dexterity reduce the profitability of various types of food production. In response to these declines, older adults are expected to shift their efforts towards low-strength yet knowledge-intensive crafts and services. Schniter et al. (2015) showed that oral tradition skills (storytelling, music performance, and dream interpretation) increase with age (Fig. 1) and that older adults aged 60 through the mid-eighties are regarded by their peers as most expert in low-strength but knowledge-intensive skills, including those in the oral tradition (Table 1). Performances in the oral tradition (music and stories) bear characteristics making them optimal for a late-life service niche: they require extensive learning and support the childrearing, socialization, and subsistence goals distributed within and between multi-generational familial groups, yet do not require physical strength.

While oral tradition performance may benefit performers and audience members by transmitting TEK, cost-benefit tradeoffs may affect the likelihood of information transmission (de Backer & Gurven, 2006). Receivers show preference for transmitters they trust and information sources they consider more reliable, and in doing so develop preferences for specific performers, performance styles, and norms for who is allowed to perform (Pinker, 1997, Scalise Sugiyama, 1996). For example, audience members in traditional societies with sex-specific divisions of labor may have reasons to prefer performances by same-sex non-parental older kin. Tsimane demonstrate same-sex vertical transmission of ethnobotanical skills and knowledge attributed to their habit for same-sex socialization and a strong division of labor along sex lines (Reyes-García et al., 2009). In Australian, Melanesian, North American, Indian, and African societies, Radcliffe-Brown (1950) observed more egalitarian relations between older relatives (e.g. grandparents) and children than between parents and children. Others have since reported this pattern of privileged familiarity between “alternate generations” (e.g., Apple, 1956, Hewlett et al., 2011, Lee, 2002). Older kin may be preferred for their greater lifetime experience (making them more trustworthy as reliable providers of honest and useful traditional information) and fewer conflicts of interest (i.e., they share genetic interests, present little to no competition for mates or available alloparenting). Furthermore, same-sex older kin are often aware of youngsters' needs, making them well poised to enrich their narratives accordingly.

In this paper, we investigate story learning and storytelling among Tsimane forager-horticulturalists. After identifying 54 story-knowledgeable adults using the Skills Survey (Schniter et al., 2015), we surveyed them about their knowledge, telling and sourcing of 120 traditional Tsimane stories. We evaluate whether age patterns in reported knowledge and storytelling are consistent with predictions derived from ECT concerning the timing of skill maturation. We test whether storytelling is a common skill enabled by ability with other common skills, or whether storytelling is a specialized skill that people develop a comparative advantage in due to productivity declines with other skills. We also assess whether storytelling propensity is sensitive to the size and composition of potential audiences, consistent with a fitness-enhancing strategy. Finally, we evaluate whether reports of whom stories were learned from support a model of vertical, oblique, or horizontal oral tradition transmission.

Tsimane (population ~ 16,000) are forager-horticulturalists inhabiting the southern reaches of the Amazon Basin in Bolivia. Although Tsimane were exposed to Jesuit missionaries in the late 17th century, they were never successfully settled into missions and remain relatively isolated from the larger Bolivian society, speaking their own language and little Spanish. Tsimane assume semi-sedentary residence in 90 + kin-based villages (with between approximately 50–150 people) that vary in river and road access, surrounding game densities, recent local deforestation, and access to market goods. Over 90% of the Tsimane diet derives from nonmarket sources (Martin et al., 2012). Tsimane subsistence stems primarily from adults' gardening, gathering, hunting, and fishing– activities that entail risks and complex extraction challenges. To meet these challenges, Tsimane transmit a rich body of knowledge to inform youngsters who eventually will master the necessary extraction techniques after decades of practice (see Table 1). Tsimane use their stories, music, and dream interpretation to assist with traditional knowledge transmission.

Stories are typically broadcast in group settings and tailored to audiences. In contrast with other forms of information transmission targeting individuals, stories do not typically involve visual examples, direct instruction, correction, or encouragement associated with various forms of skill instruction and pedagogy.

Tsimane retell traditional stories and tell of dreams and hunts. Storytelling is much less common than the musical performance or dream interpretation that the majority of adults 60 and older report. While only 5% of adults 15–29 years old tell stories, the proportion of storytellers is higher with age: 44% of oldest adults (60 + years old) tell stories (Fig. 1). Tsimane traditional stories show the same thematic elements consistently noted across populations: they communicate information about society, spatial knowledge, hazard avoidance, and local subsistence knowledge. In Appendix A and B, Tsimane myths are detailed that explain the origin of people, plants and animals, astral phenomena, and special events (e.g. solar eclipse, wildfires, windstorms). Other traditional stories describe activities and ways of life important to Tsimane: horticulture (e.g., manioc, plantain, maize, tobacco, and cotton), making fire, obtaining salt, preparing and preserving meat, acquiring metal tools, marriage, sexual affairs, and murder.

The epigraph features a translation of a typical traditional Tsimane story, taken from a larger set of Dojity and Micha stories (see Appendix A for further translations). Dojity and Micha are Tsimane culture heroes responsible for creating the earth, and stories of their adventures fall into a large variety of recognized folktale categories including hero tales, explanatory tales, animal tales, local legends, and jests (see Appendix A). The epigraph is an example of a hero tale and an explanatory tale that features a local legend: Dojity, who had created people, turns some people into animals, others into plants (including those providing the woods and canes used by Tsimane for making bows and arrows), and yet others into recognizable features of the environment (salt and the springs feeding the Pachene river), giving them the identifiable characteristics that Tsimane now use. The story excerpt in the epigraph also has elements helpful for socialization: it describes a norm violation (absconding with a married woman) and the consequence of people's angry response (wanting to kill the norm violator).

Animal tales typically feature the travels, sexual pursuits, problems, and adventures of anthropomorphized characters, and may be used to socialize children by transmitting various social norms, morals, and respect for emotions (Coe, Aiken, & Palmer, 2005b). While wolves and foxes are prominent in European folklore, as coyote is in Native North American folklore, wild felines are commonly represented across Amazonian cultures. Tsimane oral tradition features many stories with wild feline characters (e.g. jaguar, puma, ocelot): unpredictable and dangerous predators that can silently stalk humans, perch in trees unnoticed, and that become increasingly active in low light conditions when they are harder to detect (Huanca, 2006). Some traditional stories address Tsimane beliefs that trees' amo (forest spirit guardians of plants and animals) have the power to transform into jaguars (especially when angered) and that clothes made from homespun cotton can transform into jaguars during a solar eclipse (Huanca, 2006), while other stories feature the jaguar character Toyei. Appendix B details 19 stories with felines, an additional 56 fables, and 5 stories about plant spirits (e.g., O'ojpona, Úju, Opoj, Papajnaqui).

Myths and songs about amo and their abodes correspond to knowledge about seasonality of and locations for hunting and fishing. For example, a specific alignment of the Milky Way (Noco) with respect to the Maniqui river as described in a myth, serves to indicate to Tsimane “the right time to use poison for fishing” (Huanca, 2006, p. 7). The traditional story survey includes three myths with Noco (detailed in Appendix B, described in Appendix A).

While the traditional stories have established core themes that are reliably transmitted from storytellers to listeners and ultimately from one generation to the next, other Tsimane stories are personal. Personal stories may include detail about one's dreams, personal relationships, and hunting adventures. For example, Tsimane hunters may “tell the hunt”, generating vicarious experiences for their audience, while displaying ability and knowledge.² While personal stories are not part of the oral tradition, their telling may be closely tied to it. Personal information transmission is sometimes evoked by performances of traditional songs and stories mentioning wild animals or forest deities. For example, experienced hunters may volunteer elaborations about odors associated with, foods eaten by, and behavioral habits of specific animals, and confidently produce calls and vocalizations used to identify, manipulate, or describe them while providing thrilling narratives of challenges, dilemmas, and solutions to problems that they experienced.

As with storytelling skills, Tsimane also develop musical skills that are useful for effective pedagogy, communication, and entertainment. Musical performance includes instrumental music, traditional song, and improvisation. About 20% of adults 15–29 years old perform music but the proportion is higher with age: 55% of oldest adults (60 + years old) perform music (Fig. 1). Transcribed and translated examples of traditional and improvisational Tsimane songs are provided in Appendix A. When traditional melodies are played on flutes or violins in the absence of lyrics, they may serve as surrogates for corresponding lyrical speech (Sebeok & Umiker-Sebeok, 1976) that listeners easily recognize. Instrumental music as a speech surrogate has been noted across Amazonian societies (Moore & Meyer, 2014). The following is a translated excerpt from a traditional song easily recognized by many Tsimane:

tail swishing tail swishing crocodile, scales scales on the tail

trail in sand, trail in sand, trail in sand, crocodile's tail

ha ha, swimming crocodile, o o, it says angry

there it goes in the water

crawling on the floor, scales scales on the tail

went to its house like a convent

Traditional Tsimane songs provide pedagogical benefits; their lyrics reference important animals, plants, fish, and trees, and their delicate relationships with humans (Antezana, 1983, Huanca, 1999, Riester and Roeckl, 1978). Tsimane often sing personal and melancholy improvisational songs to spouses and neighbors, disclosing candid details of love affairs, sexual exploits, complaints, lamentations, and confessions. Doing so may provide therapeutic benefits and help resolve conflict by bringing interpersonal problems out into the open so that others may calibrate their responses. The following is a translation of an improvised song:

“then I won't leave you,

together we will live”.

then I won't be with you.

I will then be with another beauty.

I will live with another man then I won't want you.

I won't want you.

I will get myself another.

I will get a good husband.

Across cultures, people are motivated to interpret dreams: a process of attributing important meaning that influences judgments and impacts daily life (Morewedge, Giblin, & Norton, 2014). Among Tsimane, skilled listeners offer personalized interpretations of dreams and suggest possible omens revealed. The interpreted content of dreams can affect a number of decisions, including when to hunt, and when to avoid long trips into the forest. About 22% of adults 15–29 years old interpret dreams but the proportion is higher with age: 70% of oldest adults (60 + years old) interpret dreams (Fig. 1).

We test predictions based on two hypotheses offering distinct views about the timing and circumstances affecting traditional information transmission. The first hypothesis proposes that storytelling is a common skill enabled by expertise across all skill domains. The second hypothesis proposes that, due to its high knowledge and low strength requirements, storytelling is a specialized skill more cultivated by adults with a comparative advantage in high knowledge skills and a comparative disadvantage in skills requiring substantial strength or agility.

• Age, knowledge, and storytelling: Of all cognitive abilities, the “crystallized” abilities for vocabulary (providing definitions of words), information (answering general knowledge questions), semantic memory (names and properties of things), and comprehension (explaining why things happen) peak latest in life – during the post-reproductive lifestage (Hartshorne & Germine, 2015). Relying on these cognitive abilities, we expect that story knowledge and storytelling should not show the greater age-related declines observed in skills involving strength and motor dexterity or “fluid” cognitive abilities (Gurven et al., 2017). As a result, those older adults who know and can tell the most traditional stories, are positioned best for the specialized skill of storytelling.

• P1.1: The number of stories known accumulates with age – even into late adulthood.

• P1.2: The number of stories told is positively associated with the number of stories known, adjusting for age.

• P1.3: Older adults have a greater propensity to tell known stories.

Alternatively, if storytelling is a common skill and informants' learning and telling of stories is predicted by their abilities across all skills, we expect the null for P1.1–P1.3: story knowledge and telling will peak in mid-adulthood before declining in later adulthood.

• Costs, benefits, comparative advantage, knowledge and storytelling: The ability to learn the oral tradition may be constrained for Tsimane who are more market acculturated and more exposed to non-traditional culture. Tsimane most frequently encounter non-traditional media (radio programs, television and movies, prerecorded music, printed news) near the San Borja marketplace. Market acculturation and formal school education may lead to reduced experience with the natural environment and traditional lifestyles. This loss of experience limits a person's available time and attention for learning traditional stories (Nabhan & St. Antoine, 1993). Tsimane who are frequently exposed to non-Tsimane narratives and music (e.g. from prerecorded videos and music) may be using their limited time and cognitive resources to better learn these, at the expense of learning their oral tradition.

• P2.1: More market exposed informants with shorter market travel distance and greater market acculturation report knowing fewer traditional stories.

Alternatively, more market acculturated storytellers may experience advantages. Market acculturated Tsimane (who tend to be more educated, with better Spanish reading and writing skills) intensely and broadly provision other Tsimane in their networks (Gurven, Jaeggi, von Rueden, Hooper, & Kaplan, 2015). With more developed verbal abilities and larger social networks, market acculturated Tsimane may have more opportunities to develop traditional story knowledge.

• P2.2: Informants with greater market acculturation report knowing more traditional stories.

Potential costs to telling traditional stories (e.g. social anxiety, poor audience reception, opportunity costs) may lead storytellers to avoid telling the stories they know. However, as a specialized skill, storytellers may offset age-related declines in fitness value by telling a greater proportion of the stories they know when at a comparative advantage to do so.

• P2.3: Storytellers with comparative disadvantage in production and service domains outside of the oral tradition, but with comparative advantage in the oral tradition, tell more known stories.

• Available audience and storytelling: As a common skill, storytelling will occur among competent individuals who might tell stories to any available audience that could generate benefits (e.g. coalitionary support, deference) in exchange for the entertainment and information they are provided. Village and residential audience availability could therefore incentivize storytelling: marginal benefits may increase with the size of these audiences.

• P3.1: Storytellers with larger available village or residential audiences are more likely to tell known stories.

Alternatively, if storytelling entails opportunity costs and storytellers benefit most from a close-kin audience– audience composition may affect the propensity to tell known stories. As a specialized skill, we hypothesize that storytelling could be used to benefit inclusive fitness of the transmitter. We expect Tsimane storytelling to be biased towards the storyteller's descendants and kin, rather than indiscriminately towards any grouping of villagers able to listen.

• P3.2: Storytellers with larger available residential kin audiences are more likely to tell known stories.

• Nomination of same-sex older kin and non-parental story sources: If storytelling is a specialized skill, informants are likely to have learned their stories from select storytelling specialists. Ceteris paribus, close kin are more reliable as story sources due to shared genetic interests, and older adults may be more reliable due to cumulative knowledge and experience. Tsimane demonstrate a strong sexual division of social space and labor making same sex information transmission more convenient and appropriate for skill development. The friendliness and egalitarian power relations between children and their same-sex non-parental older relatives (e.g. grandparents) are expected to further affect story-source nomination by informants.

• P4.1: Targets who are closer in kinship, older than, and the same sex as informants are more likely to be nominated as story sources.

• P4.2: Holding kinship, older age, and same-sex constant, targets who are non-parents to informants are more likely to be nominated as story sources.

Alternatively, if storytelling is a common skill and informants learn from targets who have high ability across all skill domains, we should expect the null for P4.1 and P4.2: