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Rising Temperatures Lead To A Higher
Proportion Of Girls Being Born Than Boys
Rising temperatures in Japan lead to a higher proportion of girls being born than boys, according to a study in Fertility and Sterility. The observation has led the researchers to suggest that climate change could alter the mix of men and women.
Certain species, particularly reptiles, engage in temperature dependent sex selection, in which the sex of offspring is determined by the warmth of the environment in which eggs are incubated. Humans rely on genes, but even for us there are slightly more women conceived in tropical regions than at the poles.
Dr. Misao Fukuda found evidence to support the possibility that human sex ratios may also be influenced by temperature, although in a more subtle way and through a different mechanism.
In 1968, 1.07 boys were born in Japan for every girl. By 2012, that was down to 1.05. A similar shift has been observed in other places, but there is debate about how widespread the trend is, as well as the causes.
Fukuda also looked at data on the ratio of male to female “spontaneous fetal deaths” -- miscarriages after the first twelve weeks of pregnancy over the same period. Here the trend was much steeper, beginning at 1.3 and reaching 2 by the end of the study period.
The fact that female fetuses are more likely to survive is well-known, and there is longstanding evidence that periods of stress affect male fetuses more severely.
Changes to sex ratios for humans are so small that, unlike for reptiles, there is no threat to our survival. Nevertheless, an increase in miscarriages for all fetuses may be one more effect of rapidly changing climates.
Adaptado de: http://www.iflscience.com/environment/fewer-boyschanging-climate Acessado em 18 de outubro de 2014.
According to research published in Fertility and Sterility,
