This article discusses the variation in sex ratios at birth among human populations and the possible explanations for this variation. One possible explanation is the timing of intercourse and its relationship to the frequency of intercourse, which can affect the timing of conception. The article presents evidence that the male/female sex ratios of 148 countries declined with total fertility rates and polygyny intensity and increased with contraception use in correlational analysis. These results were independent of mother's age and level of economic development. The predictive effect of polygyny and contraception disappeared when total fertility was added to the equation. The article also considers other possible explanations for the variation in sex ratios, such as genetics, hormones, nutrition, and social factors.

This article discusses the variation in sex ratios at birth among human populations and the possible explanations for this variation. One possible explanation is the timing of intercourse and its relationship to the frequency of intercourse, which can affect the timing of conception. The article presents evidence that the male/female sex ratios of 148 countries declined with total fertility rates and polygyny intensity and increased with contraception use in correlational analysis. These results were independent of mother's age and level of economic development. The predictive effect of polygyny and contraception disappeared when total fertility was added to the equation. The article also considers other possible explanations for the variation in sex ratios, such as genetics, hormones, nutrition, and social factors.

This study attempted to replicate earlier findings regarding population structure and teen pregnancy rates. Findings support the previous predictions that sex ratio, economic development, and latitude are all inversely related to teen birth rates.

This study attempted to replicate earlier findings regarding population structure and teen pregnancy rates. Findings support the previous predictions that sex ratio, economic development, and latitude are all inversely related to teen birth rates.

This study attempted to replicate earlier findings regarding population structure and teen pregnancy rates. Findings support the previous predictions that sex ratio, economic development, and latitude are all inversely related to teen birth rates.

Can physiological variation in human populations be attributed to environmental variables? Arguing for the importance of phylogenetic comparative methods, the authors present the results of previous research by Holden & Mace (1997) on lactose intolerance as well as introduce new research on sex ratio at birth. The authors suggest that global variance in sex ratio at birth is an adapted response to the physiological costs of giving birth to boys in high fertility populations.

"This paper describes how the "sex-ratio" explanation of polygyny compares with some alternative, supposedly causal explanations. The results suggest that polygyny is best predicted by two statistically independent factors--high male mortality in warfare…and delayed age of marriage for men."

This paper presents tests of the relationships between tropical African agriculture and cultural variables regulating reproduction in order to examine a theory which suggests that the lagging or absence of tropical Africa's demographic transition is the result of pervasive 'pro-natal' cultural practices. Strength of association between these factors and non-plow agriculture, the traditional method of farming in tropical Africa, leads the authors to suggest that women's larger subsistence role in these societies favors extended family households in which child-rearing responsibilities can be shared, and polygynous marriage systems in which co-wives can contribute substantially to the family's labor productivity. These, along with erosion of regulations on postpartum sex and birth spacing which were prevalent prior to modernization, are identified as characterstics which have and will continue to resist fertility decline.

Can physiological variation in human populations be attributed to environmental variables? Arguing for the importance of phylogenetic comparative methods, the authors present the results of previous research by Holden & Mace (1997) on lactose intolerance as well as introduce new research on sex ratio at birth. The authors suggest that global variance in sex ratio at birth is an adapted response to the physiological costs of giving birth to boys in high fertility populations.

Can physiological variation in human populations be attributed to environmental variables? Arguing for the importance of phylogenetic comparative methods, the authors present the results of previous research by Holden & Mace (1997) on lactose intolerance as well as introduce new research on sex ratio at birth. The authors suggest that global variance in sex ratio at birth is an adapted response to the physiological costs of giving birth to boys in high fertility populations.