Sex ratio in Escazú, Costa Rica, 1851-1901

The long-term behavior of the secondary sex ratio (SSR) is of interest to human biologists partly because it could be responsive to cyclical environmental stress or to long-term changes in the environment. Indeed, the SSR has been reported to fluctuate in a seasonal pattern or to have a long-term trend in some populations but not in others. Here, I study the behavior of the SSR in Escazú, Costa Rica, from 1851 to 1901. Of particular interest is whether the SSR was seasonal, because Madrigal (1994) reported that in this population mortality is seasonal. The data were successfully modeled according to the Box-Jenkins methodology without incorporating a seasonal parameter. Thus the SSR did not fluctuate seasonally. For the time period under study no long-term trend was observed in the value of the SSR, which tended to fluctuate in accordance with the expected values. Finally, the behavior of the SSR was not observed to be influenced by the various epidemics that affected Escazú. These results indicate that, although severe epidemics and seasonal mortality affected the population, the community's SSR was not significantly affected by these stresses.