Humans at tropical latitudes produce more females

Skews in the human sex ratio at birth have captivated scientists for over a century. The accepted average human natal sex ratio is slightly male biased, at 106 males per 100 females or 51.5 per cent males. Studies conducted on a localized scale show that sex ratios deviate from this average in respo...

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Bibliographic Details
Published in:Biology letters (2005) 2009-08, Vol.5 (4), p.524-527
Main Author: Navara, Kristen J.
Format: Article
Language:English
Subjects:
Animals
Birth Rate
Climate
Evolutionary Developmental Biology
Female
Fertility
Geography
Humans
Male
Photoperiod
Population Dynamics
Reproduction
Sex Allocation
Sex Ratio
Sexual Behavior
Temperature
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Summary:Skews in the human sex ratio at birth have captivated scientists for over a century. The accepted average human natal sex ratio is slightly male biased, at 106 males per 100 females or 51.5 per cent males. Studies conducted on a localized scale show that sex ratios deviate from this average in response to a staggering number of social, economical and physiological variables. However, these patterns often prove inconsistent when expanded to other human populations, perhaps because the nature of the influences themselves exhibit substantial cultural variation. Here, data collected from 202 countries over a decade show that latitude is a primary factor influencing the ratio of males and females produced at birth; countries at tropical latitudes produced significantly fewer boys (51.1% males) annually than those at temperate and subarctic latitudes (51.3%). This pattern remained strong despite enormous continental variation in lifestyle and socio-economic status, suggesting that latitudinal variables may act as overarching cues on which sex ratio variation in humans is based.
ISSN:1744-9561
1744-957X
DOI:10.1098/rsbl.2009.0069