The effect of altitude on fertility in Andean countries.

Abstract In papers previously published in this journal J. M. Stycos and D. M. Heer have shown that fertility is lower in the economically underdeveloped Indian-speaking parts of Peru, Ecuador and Bolivia than in the more prosperous Spanish-speaking parts. Stycos concluded that the reason for the fertility difference in Peru is the greater marital instability of the Indian speakers which decreased their total exposure to the risk of conception. Heer suggested instead that the causes of the difference may be voluntary. The present paper questions Heer's analysis, and offers the explanation that the difference may be attributed to the physiological effects of altitude.