Parent-offspring conflict among the Karo of North Sumatra.

摘要

This dissertation analyzes the results of a quantitative ethnographic study of parental and offspring behavior among the Karo Batak. The goals of this project were to bring behavioral ecology theory to bear on demographic, economic, and behavioral data, and to assess the power of Trivers's (1974) theory of parent-offspring conflict for explaining demographic and life-history outcomes in a small-scale society. Cash-crop subsistence agriculturalists from the highlands (up to 1400m) of peri-equatorial North Sumatra, Indonesia, the patrilineal Karo Batak have relatively high rates of fertility (TFR=3.28 to 4.38) and child mortality (37.2 to 60.4 per 1,000 from birth to 5). I collected reproductive and economic histories from 240 women in two villages (Doulu and Laubuluh) with differing socioeconomic contexts, and made systematic behavior observations amongst a subsample of women. First, I tested hypotheses from a model of parent-offspring conflict resolution. As predicted, offspring that cried more during observation periods received more breastfeeding, and offspring that were ranked with more long-term "need" cried more often. I also found that offspring cry more after receiving breastfeeding, indicating that they are probably not influencing the outcome toward their own optima. Second, I presented a model of optimal interbirth intervals and some simple tests of derived hypotheses. The hypotheses met with some support, but the results from a parent-offspring conflict perspective were suggestive rather than decisive. Because landholding emerged as a strong predictor of birth intervals, I argued that the sociocultural context of inheritance may influence Karo Batak reproductive decision making. Finally, I tested hypotheses derived from two models for the timing of marriage amongst women who reported relatively complete reproductive histories for themselves and their mothers. I found support for the direct benefits model (offspring optimal perspective) but little for the indirect benefits model (parental optimal perspective). I argued that data from males might provide a better fit for the latter based on cross-cultural patterns of port for offspring marriage and reproduction. In conclusion, I found that parent-offspring conflict remains an intriguing possibility for explaining human reproductive behavior but it will be hard to come by conclusive evidence for its importance.