More Boys Than Girls Born In Warmer Years, UK

Main Category: Pediatrics / Children's Health
Also Included In: Water - Air Quality / Agriculture
Article Date: 30 Nov 2007 - 1:00 PDT

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Researchers investigating potential impact of temperature on gender, have shown that consecutive warm years can result in more men being born than women. Their findings are published yesterday in the Royal Society journal Biology Letters.

The researchers analysed the relationship between male-female sex ratios and reconstructed average temperatures. The study focuses on the nomadic Sami people of northern Finland during the 18th and 19th centuries and uses 145 years of parish records as the source of the population information.

Dr Helle, University of Turku, Finland said: "When the average temperature increased by one degree Celcius for two years, there was an increase of 1 % in the proportion of males."

The explanations for these observations are probably varied. Sperm may be influenced by heat and cold stress. Additionally, the amount of steroids such as testosterone might be influenced by temperature, resulting in a larger proportion of males. In contrast, at the other end of the gestation period, temperature induced stress could favour female survival over males due to the enhanced vulnerability of male foetuses.

Dr Helle added:"Although the precise physiological and evolutionary mechanisms underpinning these observations remain unresolved, our results do show that environmental temperature may affect human birth sex ratio."

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