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The group of primates to which our species belongs is generally active during the daytime, so deliveries start during the night and conclude in the early hours of the morning. Preserving a night-time delivery must have been very important for the survival of our ancestors from Homo erectus, 1.8 million years ago, onwards, as the intense foetal encephalization experienced by this species gradually complicated delivery, as it combined with a narrower pelvis, a consequence of bipedalism, adopted millions of years before. The oldest research into delivery time patterns is limited to hospital records from the 1930s and 1940s, before extensive medicalisation of delivery became institutionalised, and it describes a generally nocturnal pattern. The present study analyses time patterns of deliveries in two much earlier populations, from the late 19th and early 20th centuries, a total of 21,340 births in 27 years. They correspond to the Casa de la Maternidad, a charity institution initially linked to the foundling hospital in the capital, but which gradually became --during the first half of the 20th century-- the main maternity hospital in the city. The results confirm the preservation of an ancestral circadian pattern of delivery, predominantly nocturnal and in the early hours of the morning. [ABSTRACT FROM AUTHOR]

Objectives: Cohort variation in adult height expresses both the impact of socio‐economic change on human biology in a wide temporal perspective and social inequalities within populations. We aimed to test the use of joinpoint regressions to identify periods in which changes in height trends were statistically significant. Methods: Data correspond to the height recorded in Madrid City (Spain) for 65 313 conscripts between 1936 and 1974 (cohorts from 1915 to 1953), a period of social and political turmoil. Secular trends in height were analyzed in eight districts with contrasting socio‐economic conditions, grouped in two categories, lower‐class and middle‐ and upper‐class. Trends in height were evaluated by quadratic regressions and by joinpoint regressions to identify the cut‐off years when trends changed significantly. Results: Height increased in both socio‐economic categories of districts, more among conscripts from the lower‐class ones. However, results clearly show differences in trends according to district of residence. Whereas the increase in height in conscripts from the middle‐ and upper‐class districts was steady, it was slower in those from the lower classes, with declines in height during the Civil War and first years of the Franco dictatorship. Conclusions: Joinpoint analysis reveals the association between urban living conditions and adult height, and that the disparities intensified during critical historical periods of Spain. [ABSTRACT FROM AUTHOR]

Objectives: Among the ancestral characteristics of the primate group to which Homo sapiens belongs we find a pattern of daytime physical activity, but one notable exception is birthing which usually begins with night‐time labor. In populations with a moderate or high level of medicalized labor, there is evidence that the medical preferences interfere with the underlying biological mechanism for the circadian pattern of human birth. Methods: This study analyses the hourly patterns of 4,599 single live births in the House of Maternity in Madrid between 1887 and 1892, a period of very limited obstetric intervention and without the influence of artificial lighting. In order to determine the influence of natural light on labor, two periods of maximum and minimum light have been established around the summer and winter solstices of the years in question. Results: A clear circadian pattern of births emerges, with very early morning and early morning births dominating, and a sharp drop from midday until nightfall. The hourly distribution on both solstices follows this pattern, but with a clear peak shift: in winter, there is a greater concentration of deliveries in the early morning, whereas in the summer, the highest concentration is between 8 and 12 in the morning. Conclusions: The results confirm that non‐intervened human birth has a clear diurnal cycle, with a higher incidence of deliveries in the early morning or morning. The shift in distribution during the winter and summer solstices seems to confirm the effect of light on the labor process. Am. J. Hum. Biol. 26:707–709, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]