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More baby girls are born in the tropics

More baby girls are born in the tropicsThe myths and legends about baby gender and sex ratio abound. So do research studies and scientific theories.

According to the basics of biology, the sex ratio in humans should be 50:50. In reality, however, the sex ratio among newborns is actually 106 boys to 100 girls (51.5% in favour of boys). Researchers believe that this is nature’s ways of compensating for the fact that fetal and infant mortality among boys is much higher than girls. In recent years, more studies revealed some explanations about departure of sex ratio from the 50:50 norm.

A previous study has observed that sex ratio is linked to food availability. In hard times when food supply is low, it seems to be more advantageous to produce more baby boys than girls because human females need more food and energy than males when they produce eggs and become pregnant.

Another study by Italian researchers showed that seasons can influence a baby’s sex. It seems that nature favors conception of girls from March to May and boys from September to November. Again this is supposed to be linked to food supply, as autumn (at least in the northern hemisphere) is harvest time.

A recent study by researchers from the University of Georgia found even more intriguing data on sex ratio. They observed that the likelihood of having a baby girl increases with decreasing distance to the equator. This makes the sex ratio skewed, with more boys born in higher latitudes (e.g. North America, Europe) and more girls born in the tropics. The data is based on the sex ratio of newborn babies in 202 countries, from equatorial Africa up to northern Europe. Again, the reason for this skewed sex ratio is attributed to human evolution in response to food supply. Food supply in the tropics is less variable (or at least it used to be) and therefore should favor girls than in northern latitudes where there is winter to reckon with.

This is very interesting considering the fact that many countries in the equatorial region are actually culturally more inclined to favor boys than girls and may actually practice sex-specific abortion. The researchers took this into account in their analysis, with the same results.

In addition, the distribution of food supply has actually changed during the last fifty years or more due to economic development, technological advancement, and climate change. What we see now is that the more developed countries in higher latitudes have ample food supply whereas many areas in the tropics are experiencing food shortage due to droughts, floods, and typhoons. If the sex ratio is really linked to food supply, then we would expect a shift in the future for more girls to be born in Europe and North America. However, evolution is a slow process so we probably won’t see this shift in our lifetime.

The study only considered mothers and babies who actually live in those geographical regions. In other words, there is no guarantee that you’ll have your baby girl by simply spending a holiday in a tropical destination.

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