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ShareLondon: Longing for a baby girl? Go and settle down in the tropics. Yes, bizarre, it might seem but a new study has found a link between latitude and sex of babies.
Researchers in Greece have claimed that variations in temperature and day length which depend on latitude could explain the differences, but there's no obvious explanation, the 'New Scientist' reported.
The study is based on global birth data collected by the US spy agency CIA between 1997 and 2006 in 202 countries.
The global average from the data worked out at 51.3 per cent of all births being boys, or 105 for every 100 girls born. At tropical latitudes, the ratio of males born fell to 51.1 per cent, compared with 51.3 per cent in temperate and subarctic latitudes -- the same as the global average.
"Of the 20 countries with the lowest ratios, 18 were at tropical latitudes," lead researcher Kristen Navara of the University of Georgia in Athens said.
And even though the differences might appear small, they translate into large numbers of babies. Of the girl-rich tropical countries, the Central African Republic was the only one where more girls than boys were born in the 10-year study, with a ratio of 0.49 per cent.
The researchers have pointed out that although this figure appears small, it translated in 2006, for example, into 1400 fewer boys than if the ratio was 50:50.
Other tropical countries with low male birth ratios included Grenada (50.2 per cent), Mauritius (50.3 per cent), Liberia (50.7 per cent) and the Bahamas (50.5 per cent). These compared, for example, with gluts of boys in Asian countries, such as South Korea (52.6 per cent), Armenia (52.2 per cent) and China (52.8 per cent).
"Of the 10 countries producing the lowest sex ratios, only three are from Africa, leaving seven which have never been linked to practices of sex-selective abortion. It's very difficult to explain," Navara said.
According to her, in Siberia in winter, when days are shorter, more males are born. So, more females are born if day lengths are longer, tallying with the finding in humans. "We think this may be mediated by the hormone melatonin, which is responsible for causing major reproductive changes in response to day lengths."
The findings are published in the 'Biology Letters' journal.
