Future Discounting Explanation for the Persistence of a Mixed Foraging Horticulture Strategy among the Mikea of Madagascar

Bram Tucker

This chapter pursues dual goals. The first goal is to argue in favor of the use of future-discounting concepts when modeling choices among subsistence activities with dissimilar delay to reward, such as the choice to practice foraging versus farming. While foraging theory makes the value of all options commensurate by expressing them as a rate of gain per unit time, people may subjectively devalue options with long waiting times, such as agricultural harvests. A literature review and guide to discount rates are presented for readers unfamiliar with these concepts. The second goal is to demonstrate the applicability of future discounting models by presenting a simple dynamic model explaining why Mikea of Madagascar prefer labor-extensive cultivation despite the high risk and low mean payoff, and despite their familiarity with the techniques and benefits of intensive farming. Mikea cultivate because the rewards are high compared with foraging, but they refrain from intensification because immediate needs limit their capacity for future investment.

Low-investment extensive horticulture, the planting of cultigens with minimal labor invest ment in patches of wilderness that remain more-or-less untended until harvest time, seems a curious strategy. Payoffs tend to be low on average, for the cultigens compete with wild plants for soil and solar resources. Returns are also highly variable, for the crop is left vulnerable to pests, predators, and unpredictable climatic conditions. Extensive horticulturalists compensate for low and variable harvests by hunting and gathering wild foods, which constitute the bulk of the diet in some years. Given this heavy reliance on foraging, one may well ask why plant cultigens at all? Conversely, why refrain from intensifying agricultural inputs to produce a more dependable and satisfying agricultural payoff?

As curious as the foraging/low investment horticulture strategy may appear, archaeological evidence suggests this was a persistent strategy for millennia in many parts of the world. Some of the first cultigens may have been domesticated rather rapidly, in the span of 20 or so plant generations (Hillman and Davies 1990a, b; Hillman and Davies 1992). There followed a long period of time in which people continued to rely primarily on foraging while horticulture played an ancillary role. According to Bruce Smith (2001a), this middle ground between plant domestication and intensive farming lasted 3000 years in the Near East, 4000 years in some parts of North America and Europe, and 5500 years in central Mexico (see also Piperno and Pearsall 1998; Doolittle 2000).

Archaeologists interested in subsistence decisions have as a guide the behavior of living peoples, observed and documented with ethnographic and experimental methods and informed by evolutionary theories of human behavior (O'Connell 1995). This chapter describes Mikea of southwestern Madagascar, a contemporary ethnographic population who combine low-investment maize and manioc horticulture with foraging for wild tubers, honey, and small game.

The most important subsistence and cash crop for Mikea was, until recently, maize grown in slash-and-burn fields called hatsake (the "ethnographic present" for this chapter is before the government effectively banned hatsake cultivation in 2002). Mikea invest little labor and no other inputs into their maize fields. New fields are cleared by felling and burning trees. Old fields are reused for several years and then abandoned. They are usually cleared of weeds and saplings before planting, although some farmers reduce labor costs even further by planting among the weeds. After planting, no additional labor is invested until harvest time. The fields are exposed to severe sunlight, unpredictable rainfall, poor soil nutrition, weedy competition, and predation by grasshoppers and unsupervised herds of cattle and goats. Mikea are aware of a variety of intensification techniques that could increase maize yields and reduce risk of failure, such as tillage, irrigation, manure fertilizers, weeding, enclosure, and field guarding, but they rarely practice these. Instead, they return to their fields three months after planting and harvest whatever happens to be there.

Most Mikea households in the study area also grow manioc in permanent fields in the savanna, alongside their Masikoro agropastoral neighbors. Masikoro cultivate manioc semi-intensively on a 12-to 15-month schedule. Some farmers plant in plowed furrows or mounds, and dig drainage ditches to avert flood damage; and they weed their fields three to four times a year. Fields are enclosed with fences and guarded with talismans to protect them from animal, human, and supernatural predators. Forest-dwelling Mikea rarely practice these techniques. Because they only check their fields during periodic visits, they often neglect to drain or weed in a timely fashion, if at all. Loss to livestock and thieves is common. Even when alerted that their field was being plundered by thieves in the night, two brothers in 1998 refused to save their crop, insisting that the wild tubers and honey in the forest were sufficiently plentiful.

Are Mikea cultivation decisions irrational? As foragers, Mikea are viewed as primitives who have yet to discover the intensive farming techniques of their more "advanced" Masikoro neighbors. Their horticulture would appear to be a transitional stage between foraging and farming. But such unilinear-evolutionary assertions are contradicted by Mikea ethnohistory and oral history, which indicate that Mikea and Masikoro are historically the same people. Mikea are descended from Masikoro who sought refuge in the forest to escape the slave raids and tribute demands of the Andrevola kings, and during the French colonial era, to avoid mandatory resettlement and taxation (Yount et al. 2001; Tucker 2003). Foraging is not just an occupation; it is symbolically significant to Mikea identity as refugees from An-drevola hegemony. Mikea have probably always planted some cultigens in combination with foraging. Fanony (1986, 139) reported Mikea cultivating crops in the late 1970s. Twenty years earlier, Molet (1958) documented maize and butter beans in swidden patches deep in the Mikea Forest. Mikea oral histories from the nineteenth century are replete with references to forest fields of maize, manioc, sweet potatoes, rice, sorghum, and taro (Tucker 2003). Shipwrecked sailor Robert Drury, circa

1710, observed that foragers of southern Madagascar "content themselves with small plantations" in addition to "the products of nature" (Drury 1826 [1729], 139). Mikea are active participants in Masikoro society, and indeed, all Mikea self-identify as being either Masikoro or Vezo in addition to Mikea. Mikea and Masikoro belong to the same clans, intermarry freely, and participate in the same family ceremonies. Mikea often labor in their neighbors' fields for wage payments. So Mikea and Masikoro share the same knowledge of agricultural intensification techniques. Masikoro choose to intensify; Mikea do not. Nor do Mikea choose to specialize on foraging. For centuries many have chosen a middle path.

Which is most profitable: foraging or cultivation? This depends on how one defines "profitable." Agricultural profitability is usually measured as yield per unit of land. But because mobile foragers' harvest is not land-limited, it makes little sense to quantify wild tuber production as kilograms per hectare.

Alternatively, we can compare foraging and farming with the logic of foraging theory. Foraging theory calculates rewards as a net rate of energy gain, or net acquisition rate (Pyke et al. 1977; Stephens and Krebs 1986, 9). When digging wild ovy tubers (Dioscorea acuminata), Mikea children average 500 net kcal/hr, while adults gain 1200-2700 kcal/hr (Tucker and Young 2005). If cultivated rewards are calculated in the same manner, then foraging is clearly an inferior choice. The most extensive form of Mikea cultivation is planting maize in an unweeded hatsake field, for which the only required investment is 11 person-hours of planting labor per hectare. The net acquisition rate is approximately 165,215 kcal/hr.1 In a survey of 247 hatsake in 1998 and 1999, only 6.5% of fields were cultivated in this manner. In the majority (57%) people cleared weeds before planting, adding an extra 24.7 person-hours of labor investment to the venture. This increases average yield from 500 kg/ha to 910 kg/ha. But the net acquisition rate is actually lower: 92,469 kcal/hr.2 Net acquisition rate does not adequately describe the value of foraging and farming, nor does it explain the costs and benefits of intensification.

I argue that the best way to model the choice between foraging versus cultivation is with a future-discounting model. When offered a choice between a small reward available now versus a larger reward after a delay, decision-makers often prefer immediate gratification, indicating that they subjectively devalue rewards for which they must wait (Samuelson 1937; Mazur 1984, 1987; Rachlin et al. 1991; Myerson and Green 1995; Green and Myerson 1996; Frederick et al. 2002). To borrow Wood-burn's (1980) terms, foraging is an "immediate return" economic system while farming is a "delayed return" economic system. The reward for a few hours' foraging is a certain catch of food: small in comparison to an agricultural harvest, but available for immediate consumption. A day spent cultivating is rewarded with sweat, blisters, and an empty stomach, along with the promise of a large quantity of food some time in the future. Exogenous factors such as high risk of crop loss may make agriculture an empty promise. Factors endogenous to the household, such as food supply adequacy, may limit a household's ability to survive on promises alone. Mikea cultivate because the rewards are high compared with foraging, but they refrain from intensification because immediate needs limit their capacity for future investment.

This chapter has two goals. The first is to present a theoretic argument for the use of a future discounting framework when modeling the choice to forage or to farm. I begin with a critical evaluation of the way foraging theory deals with time. Then I present a brief review of descriptive models, methods, and explanations from future discounting studies in economics, psychology, and anthropology. I follow with a guide for modelers to choosing discount rates. The second goal of this chapter is to illustrate the applicability of future discounting to modeling subsistence decisions. To this end I return to the Mikea example provided above, and present a future-discounting model to explain why Mikea practice a mixed foraging-horticulture strategy.

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