Historical Mortality Dynamics on the Baja California Peninsula : Marriage, Mining Booms, Migration, and Infectious Disease.

Historical demographic research shows that the factors influencing mortality risk are labile across time and space. This is particularly true for datasets that span societal transitions. Here, we seek to understand how marriage, migration, and the local economy influenced mortality dynamics in a rapidly changing environment characterized by high in-migration and male-biased sex ratios. Mortality records were extracted from a compendium of historical vital records for the Baja California peninsula (Mexico). Our sample consists of 1,201 mortality records spanning AD 1835-1900. Findings from Cox proportional hazard models indicate that (1) marriage was associated with a protective effect for both sexes; (2) residing in a mining town was associated with higher mortality for men, but not women; (3) migration was associated with decreased mortality risk for women, but not men; and (4) the risk of mortality increased in the face of infectious disease, but decreased over time. Despite the early initiation of reproduction for women, marriage had a protective effect, likely because marriage linked women to resources. Although mining boomtowns were associated with elevated risk factors generally, only men experienced greater mortality risk, likely due to dangerous working conditions that women did not experience. Last, female, but not male, migrants experienced greater longevity, possibly because exposure to harsh labor conditions eroded the protective effect of selection bias for men. Together, these results shed light on an understudied historical population and broaden our understanding of demographic dynamics in preindustrial settings.

NDVI predicts birth seasonality in historical Baja California Sur, Mexico: adaptive responses to arid ecosystems and the North American Monsoon.

Birth seasonality is a phenomenon whereby populations can be characterized by a single month or season in which births peak. While non-human animal research suggests that seasonal birth-pulses are related to variation in climate and local energy availability, social scientists debate the mechanisms responsible for it in humans. Here we investigate the role of precipitation, temperature, and energy availability on seasonal conception and birth pulses using a historical dataset from the Baja California peninsula - a hot, arid desert that experiences seasonal climatic fluctuations associated with the North American Monsoon. Analyses suggest that 1) local energy availability had a negative relationship with conception pulses; and 2) birth pulses had a positive relationship with local energy availability and a negative relationship with temperature. Taken together, our analyses suggest that women timed conceptions when local energy availability was lowest (challenging expectations of conception rates as simply reflecting ecological influences on female fecundity), so that children were born during the seasonal "green-up" associated with the North American Monsoon. Given our results, we speculate that birth seasonality represents a form of traditional ecological knowledge to improve neonate health and wellbeing.

Marriage dynamics in old Lower California: ecological constraints and reproductive value in an arid peninsular frontier.

It is commonly expected that natural selection will favor earlier reproduction, yet ecological constraints can force people to delay marriage. Furthermore, humans demonstrate sex-specific preferences in marriage partners - with grooms normally a few years older than their brides; however, the age at which individuals marry can influence the spousal age gap. We investigate factors influencing age at first marriage and age difference at marriage using nineteenth-century historical demographic data from Baja California Sur, Mexico. Analyses suggest ecological constraints affected male, but not female, age at first marriage. Males who migrated from their natal community and who married in communities whose primary economic activity was agriculture experienced delayed age at first marriage. The age at which females first married increased over time causing a reduction in the age gap between spouses. Furthermore, the spousal age gap showed sex-specific effects: women who married early in life were much younger than their husbands, while women who married late in life were older than their husbands, suggesting that variation in female reproductive value influenced mate choice. Males, on the other hand, who married late in life showed a preference for marrying much younger females, indicating preferences for females with high reproductive value.

POPULATION GENETICS. Genomic evidence for the Pleistocene and recent population history of Native Americans.

How and when the Americas were populated remains contentious. Using ancient and modern genome-wide data, we found that the ancestors of all present-day Native Americans, including Athabascans and Amerindians, entered the Americas as a single migration wave from Siberia no earlier than 23 thousand years ago (ka) and after no more than an 8000-year isolation period in Beringia. After their arrival to the Americas, ancestral Native Americans diversified into two basal genetic branches around 13 ka, one that is now dispersed across North and South America and the other restricted to North America. Subsequent gene flow resulted in some Native Americans sharing ancestry with present-day East Asians (including Siberians) and, more distantly, Australo-Melanesians. Putative "Paleoamerican" relict populations, including the historical Mexican Pericúes and South American Fuego-Patagonians, are not directly related to modern Australo-Melanesians as suggested by the Paleoamerican Model.