Influence of birth interval and child labour on family energy requirements and dependency ratios in two traditional subsistence economies in Africa
Ulijaszek, S.J.
Journal of Biosocial Science 25(1): 79-86
1993
ISSN/ISBN: 0021-9320 PMID: 8425889 DOI: 10.1017/s0021932000020320Document Number: 321687
The value of children to their parents can be as a source of labor which adds to the household economy. This study examines the effect of different birth intervals on family size, energy requirements, and energy dependency ratios (EDR) within the family life cycle. The ratio of the amount of work required to generate sufficient dietary energy (the output-input ratio; OIR) is examined at different levels of child labor. Gambian agriculturalists and the ]Kung hunter-gatherers of the Kalahari Desert, as traditional natural fertility populations, are the subjects of the investigation. The ]Kung OIR is reported as 9.5 during the high energy food-gathering season compared with a Gambian OIR of 11.2. Children are born within a 15-20 year reproductive time span and do not contribute to family subsistence until marriage. Study energy requirements were modeled on 21-, 30-, and 44-month birth intervals and 45-year life cycles (every 5 years) and were based on the UN Food and Agricultural Organization's recommendations based on basal metabolic rate (BMR) for body weight and activity level of each study population. Energy requirement is considered the equal to habitual levels of physical activity. The energy requirement for Gambian males was estimated at 1.52 and for females 1.82 times BMR, and 1.65 times BMR for ]Kung males and females. A mean level of activity took into account physical activity for working and nonworking days. The assuptions made in the model are identified for both the sum of energy requirements for children and adults and the OIR needed to sustain family energy requirements. Compensation is made for measurement errors. The results show that energy requirements peak for Gambians at 20-30 years and for ]Kung at 15-20 years. The peak EDR for the ]Kung is 15 years and for Gambians 10 years. Lower OIRs are possible when child labor is involved in subsistence at all levels of child spacing. A similar OIR of 15.4 is found for ]Kung at a 44-month birth interval and child labor of 0.1 BMR for Gambian birth intervals of 21 months. Older adolescents who are dependents in either society are a drain on resources. There is no advantage to child labor for any birth interval and at any level of child input. High fertility among ]Kung bushmen would not be an advantage.