Adaptations to resource constraints during the pretransitional era: Fertility differentials arising from the peopling of the Thai frontier.

Taking a human ecology perspective, we investigate the effects of population pressure on provincial variations in fertility during the 1950s in Thailand. The research is motivated primarily by Easterlin's investigation of frontier effects in 19th century North America. We hypothesize that during the period prior to Thailand's remarkable economic expansion and fertility decline, both in-migration and rural fertility should vary positively with the availability of arable land. Also, we anticipate that the major proximate determinant of these rural fertility differentials will be exposure to intercourse, i.e., marriage patterns. We find a high correspondence among measures of land availability, migration, and fertility, and find that they were all high in many provinces located across Thailand's heartland. Multivariate analysis indicates that while sex ratio imbalances and early marriage account for much of the relatively high fertility in these frontier provinces, a substantial direct effect of population density on fertility within marriage remains. We discuss the implications of the findings.(Authors abstract)