Patrones reproductivos en la altura: ¿hipoxia o regulación cultural?

Descripción de las características reproductivas en la altura basada en los datos recogidos en 1988-99 en 10 comunidades Aymará que viven a una altura promedio de 4000m en el Altiplano Boliviano. Se registraron las historias reproductivas de 868 mujeres casadas, la población femenina total, de las cuales 359 tenían entre 45 años y mas. El modelo reproductivo se presenta con un comienzo tardío de la fertilidad, y un comienzo tardío de los embarazos, asociado con un corto periodo reproductivo y con amplios intervalos entre nacimientos. Estas características podrían ilustrar las disminuciones de los procesos de fecundidad o fertilidad por hipoxia. Sin embargo, las condiciones ambientales explicarían la tardía edad a la menopausia de jóvenes rurales comparadas a jóvenes urbanas, mientras que la edad al primer nacimiento puede depender más de un control cultural. El corto periodo reproductivo parece resultar de un amplio intervalo promedio entre el ultimo nacimiento y la menopausia, determinado esencialmente por decisiones culturales. Los intervalos entre nacimientos, más largos que en muchas sociedades tradicionales, podrían ilustrar una recuperación más lenta de la fecundabilidad post-partum inducida por la hipoxia, pero la dura forma de vida en el Altiplano (bajas condiciones sanitarias y nutricionales y alta carga de trabajo) podría también explicarlo. Por un lado la existencia de control de nacimientos, y por otro la tasa de fertilidad de 6 nacimientos vivos entre las parejas que no practican contracepción, son además argumentos en contra la hipótesis que sostiene que la fecundidad puede estar afectada por la hipoxia en estos grupos Aymará.Asociación de Antropología Biológica de la República Argentin

Boys are more stunted than girls in Sub-Saharan Africa: a meta-analysis of 16 demographic and health surveys

BACKGROUND: Many studies in sub-Saharan Africa have occasionally reported a higher prevalence of stunting in male children compared to female children. This study examined whether there are systematic sex differences in stunting rates in children under-five years of age, and how the sex differences in stunting rates vary with household socio-economic status. METHODS: Data from the most recent 16 demographic and health surveys (DHS) in 10 sub-Saharan countries were analysed. Two separate variables for household socio-economic status (SES) were created for each country based on asset ownership and mothers' education. Quintiles of SES were constructed using principal component analysis. Sex differentials with stunting were assessed using Student's t-test, chi square test and binary logistic regressions. RESULTS: The prevalence and the mean z-scores of stunting were consistently lower amongst females than amongst males in all studies, with differences statistically significant in 11 and 12, respectively, out of the 16 studies. The pooled estimates for mean z-scores were -1.59 for boys and -1.46 for girls with the difference statistically significant (p < 0.001). The stunting prevalence was also higher in boys (40%) than in girls (36%) in pooled data analysis; crude odds ratio 1.16 (95% CI 1.12–1.20); child age and individual survey adjusted odds ratio 1.18 (95% CI 1.14–1.22). Male children in households of the poorest 40% were more likely to be stunted compared to females in the same group, but the pattern was not consistent in all studies, and evaluation of the SES/sex interaction term in relation to stunting was not significant for the surveys. CONCLUSION: In sub-Saharan Africa, male children under five years of age are more likely to become stunted than females, which might suggest that boys are more vulnerable to health inequalities than their female counterparts in the same age groups. In several of the surveys, sex differences in stunting were more pronounced in the lowest SES groups

Sex Ratio at Birth and Mortality Rates Are Negatively Related in Humans

Evolutionary theory posits that resource availability and parental investment ability could signal offspring sex selection, in order to maximize reproductive returns. Non-human studies have provided evidence for this phenomenon, and maternal condition around the time of conception has been identified as most important factor that influence offspring sex selection. However, studies on humans have reported inconsistent results, mostly due to use of disparate measures as indicators of maternal condition. In the present study, the cross-cultural differences in human natal sex ratio were analyzed with respect to indirect measures of condition namely, life expectancy and mortality rate. Multiple regression modeling suggested that mortality rates have distinct predictive power independent of cross-cultural differences in fertility, wealth and latitude that were earlier shown to predict sex ratio at birth. These findings suggest that sex ratio variation in humans may relate to differences in parental and environmental conditions

New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens

Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315?±?34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent