«By Nathan B. Goodale A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY WASHINGTON STATE ...»
women would have the equivalent of more than four hours of intensive exercise a week), intuitively it is not exercise intensity that is influencing fertility but instead the duration of their lives in which they engage in exercise. In this scenario, women would be most prone to infertility due to intensive exercise for the first nine years after menarche. Ethnographically, most females in societies practicing huntergatherer subsistence strategies do not extensively contribute to the economic means of the family until 20+ years of age (Kramer and Boone 2002). If this were the case preceding the Neolithic, it is possible that hunter-gatherer women living before the Neolithic may not have engaged in more than ten years of intensive exercise preceding the onset of typical child-birthing years. This likely changed with the transition to agriculture, where females ethnographically begin to make a significant economic contribution by the age of 13 (Kramer and Boone 2002), suggesting that they may have engaged in intensive exercise earlier in their lives than that of huntergatherer women. The implications of this are that there may be a significant link between exercise, fertility, and the TFR between women participating in huntinggathering versus agricultural subsistence modes; the later has the potential for significantly higher TFR.
Another issue somewhat related to the amount of exercise correlated to fertility is the amount of food an individual consumes. Related to the quantity of resources and the cyclical nature of the amount of food available throughout the year in a hunter-gatherer context, Van der Walt et al. (1978) found that San women in
was short. In general, seasonal short falls suppressed ovulation annually, which in hunter-gatherers could have been one mechanism that maintained small population sizes and densities with little dramatic change through time. However, under circumstances where agriculture and delayed return subsistence practices with the advent of storage technology were practiced, seasonal menstrual cycles could be maintained, although climatic variability and reduced crop productivity could have dramatically affected population levels. Logic would indicate that storage would permit more stable diets in terms of quantities; but even with agricultural practices, crop failure over the long-term or even short-term could result in catastrophe. This can be theoretically graphed in Figure 4.4. Note that once storage technology and cultivation are employed, when problems associated with crop failure, the effects may be of a much higher magnitude than when foraging strategies were employed (Figure 4.4).
A simple graph of diet stability before and after the invention of intensive storage technology. Note that peaks above and below the high diet stability line indicate seasonal use of different foods. After storage is in place, certain foods would have been available for a long-term basis providing much more stabilized diets.
fertility appears to show a correlation where the duration (both in terms of hours and years) could have provided a situation for better reproductive health in agricultural than hunter-gatherer societies. Additionally, seasonal short falls may have influenced ovulation suppression in forager societies, which resulted in maintaining overall population sizes small but overall more stable. In contrast, agricultural systems may have promoted the quantities of food needed for sustained ovulation, but in bad times, population crashes could have been more severe. While not directly measurable, these appear to be at least two influencing factors for why fertility increased during the transition to agriculture; however, what are the other factors of changing life ways should have promoted parents to invest in rearing more offspring?
Optimality, Child Rearing and Economic Systems “It is impossible to predict fertility on the basis of subsistence alone” Bentley et al. 1993b:779 There is a growing body of literature that links the relationship between optimality to different subsistence modes, population growth rates, and natural fertility rates (Bentley et al 1993a, b; Boone 2002; Campbell and Wood 1988;
Hewlett 1991; Kramer and Boone 2002; Munroe et al. 1984; Stecklov 1999; Sellen and Mace 1997) and to a lesser extent, the amount of work contributed by different sexes as well as different age groups (Kramer and Boone 2002). As noted in Chapter Two, evolutionary theory predicts that humans have a finite amount of energy, and
(procuring food and shelter) and reproductive interests in terms of time spent in the process of finding mates and child rearing. Because humans have a finite amount of energy to ensure their reproductive success (discussed in Chapter Two), the number of children they can support is directly proportional to their ability to provide for their dependents as well as themselves. However, it seems intuitively correct that population growth and expansion during the NDT had to incorporate some negotiating factor that allowed for larger families.
Work Loads, Age Structure, and Subsistence Mode When collecting or processing resources, the amount of time and energy invested is the labor cost of some defined unit of food. The time and energy increases in turning the resource into usable end products in relationship to the net return. This is referred to as subsistence intensification (Boserup 1972; Kramer and Boone 2002:512). The transition to agriculture fits this definition in most instances where there is decreased labor efficiency when the procurement is less energy-efficient than regular foraging (Kramer and Boone 2002; Bettinger 2006). This is generally argued to be due to factors related to not only increases in harvest and processing investments, but also to time spent maintaining fields and irrigation channels as well as planting.
Several studies related to subsistence mode and the gender/age groups that participate in the economic enterprise of harvesting food suggest that the addition of
in the time and resources devoted to raising a family (Bentley et al. 1993a, b;
Campbell and Wood 1988; Hewlett 1991; Kramer and Boone 2002). In terms of active work between subsistence modes, Sackett’s (1996) case study of 102 groups of agriculturalists, horticulturalists, and foragers focused on time spent engaged in active labor, and the study suggests major differences between hunter-gatherer and agricultural subsistence strategies. The results indicate that people practicing an agriculture subsistence mode spend many more hours a day engaged in food-related work than do foragers or horticulturalists.
Low (2000:144-145) notes the basic pattern that when offspring must compete for limited resources, parents shift their attention to investment in offspring rather than production of offspring, and unless there is a significant increase in resources, fertility rates will reflect this pattern. Additionally, Malthus (1970) argues that population size is restricted by the state of food production, or in other words, that technological improvements in combination with the amount of resources available control population growth.
Nonetheless, just because a woman can get pregnant does not necessarily mean that she will choose to raise more children. Agricultural groups around the world have significantly higher fertility rates than foragers and horticulturalists (Figure 4.5 and Table 4.1) (Bentley et al. 1993a; Boone 2002). It is important to explore the reasons to invest in those offspring that added to population growth witnessed during the early phase of the NDT. In other words, why was population
during the NDT?
Total Fertility Rates (TFR) of 57 ethnographic groups subdivided by subsistence mode. Redrawn after Bentley et al. (1983a) with data from Appendix I and Boone (2002:16).
There are many examples in the ethnographic record where infanticide is utilized as a means to negotiate the social pressures of bearing and raising children (Hill and Hurtado 1996; Hewlett 1991). A search of infanticide in the HRAF database yields 769 matches in 80 cultures around the world. While infant death is more often a consequence of predators or other humans that may be reproductive competitors (Low 2000:75), infanticide does occur among genetic parents and is usually a way to either manipulate mating strategies to provide equal opportunities for each sex or because one sex may have a higher reproductive value based on wealth
between 15-50 percent of infants died due to limited resources. Logically it can be argued that there is an evolutionary benefit for either having and raising more children or the opposite, for not investing in more children. Consequently, there should be social components in settled societies that would promote child bearing/rearing that were relatively absent in mobile hunter-gatherer societies.
Total Fertility Rates of 57 Forager, Horticultural, and Agricultural groups.
Data is after Bentley et al. (1998).
With this in mind, the NDT must have incorporated some restructuring of the socioeconomic system and potentially who could participate. Kramer and Boone (2002) suggest that data from Maya agricultural families indicate that children make economic contributions to food acquisition much earlier than horticultural and forager groups. Kaplan (1994, 1996) documents that among the foraging Machiguenga, Piro, and Ache that dependent offspring provided only around 20 percent of the total food that they consumed. Additionally, these dependents did not become net producers until their 20s, when they started having children of their own. In the case of Maya children, Kramer and Boone (2002) find that children become net producers as adolescents, five to seven years before they reproduce and while still living with their
large families selected for wealth and status (the wealth-flow hypothesis of Caldwell ), but instead to underwrite the cost of younger dependent siblings. In this circumstance the answer to the question of who keeps children alive may be predominantly themselves, in the case of non-dependent children, and predominantly their siblings, in the case of dependent children under an agricultural subsistence strategy (Kramer and Boone 2002). Additionally, it appears that “children’s work funds parents’ continued reproduction rather than wealth per se” (Kramer and Boone 2002:516). We could also expect that parents may benefit in other ways through this relationship where energy not invested in child rearing compensated for by nondependent offspring may be invested elsewhere.
Epipaleolithic through Neolithic: A Case Study from the Near East One potential place that parents may have been investing energy that has archaeological correlates in the early part of the NDT in the Near East is an expansion in the number of social roles among Early Neolithic versus Epipaleolithic communities as indicated by the development of more spatially defined communities, indicated by prepared activity area floors, formalized middens and much more investment in the scale of architecture (Kuijt and Goodale 2009). These elements are largely absent from Natufian communities (Hardy-Smith and Edwards 2004). The activities associated with these developments may be the social outcome that
adaptive systems by adding younger children to the work force.
If Kramer and Boone (2002) are correct, and this case study can be applied to other regions of the world, one explanation for the why the transition to agriculture and the NDT happened may then be significantly correlated to the introduction of younger non-dependent offspring into the work force. This likely enabled parents to explore other social niches, including investments in exploring new technologies such as food storage. The origins of agriculture may then be viewed both as an economic revolution but also as a means in which to engage children into the entire economic process. Kramer and Boone (2002:514) articulate very clearly at least in terms of the Puuc Maya community of agriculturalists that “parents’ work effort alone does not meet the family’s combined labor requirements” (emphasis in original). In other words, the parents alone were not producing enough food to meet the daily requirements of the family as a whole.
Summary In this chapter I have outlined several concepts associated with not only detecting a NDT in the Near East, but also significant correlates that may provide an explanatory framework in terms of why fertility increased, as well as how to compensate for limited energetic budgets of bearing and raising more children. This includes the development of storage techniques that allowed wild foods to be stored for longer than the harvest season. Importantly, these foods are correlated with high
allowing higher population densities. Moreover, I have argued that a potential social impetus for investing in more children which produced the “substantial increase in human numbers” (Bocquet-Appel 2002), was the shifting social roles of a younger age bracket to the work force.
While it is out of the scope of this project to directly test the effects of the fertility diet on a large scale demographic transition due to the restricted nature of the Nurse’s Health Study data, we can examine the direct correlates of when it may have started to influence female fertility. We can also not directly test the addition of younger age classes into the work force; however, it appears that in general, kids contribute more to the economic system in agriculture than in hunting and gathering contexts.
The cultural chronology of the Near East encompasses some of the most interesting advances in human culture and evolutionary adaptation. These include the advent of subsistence intensification potentially as early as 14,500 cal BP during the Early Natufian, invention and use of systematic cultivation and food storage sometime after 12,000 cal BP in the Pre-Pottery Neolithic A (Bar-Yosef 2004;