Resource Competition and Reproduction in Karo Batak Villages

Geoff Kushnick, University of Washington

Behavioral ecology theory predicts that when wealth is heritable, parents may (1) manipulate family size to optimize the tradeoff between more relatively poor offspring and fewer relatively rich ones; and (2) channel less care into offspring who compete more with their siblings for resources. These hypotheses were tested with 305 Karo Batak boys. The Karo Batak are patrilineal agriculturalists from North Sumatra, Indonesia, among whom land is bequeathed equally to sons. As predicted, the relationships between reproductive rate and parental investment on one hand, and number of sons on the other, was mediated by landholding. Reproductive rates slowed with increasing sons among families with above-average landholdings, but not among the landless and those with small landholdings. Age-five mortality increased with the number of sons more steeply among landowners than among the landless. Finally, immunizations decreased with the number of sons among landowners, but increased among the landless.