More girls are born closer to the equator

More boys than girls are born all over the world, but a study has found that the closer people live to the equator, the smaller the difference becomes. No one knows why.

The skewed sex ratio at birth has been known for more than 100 years... researcher Kristen J. Navara of the University of Georgia performed a statistical analysis that found the effect of latitude persisted across wide variations in lifestyle and socioeconomic status... The correlation with latitude was unchanged even after excluding data from countries that might have been skewed by abortion or the killing of baby girls...

Hamsters, mice and meadow voles also produce more male offspring during shorter days or colder weather, but the reasons in these animals are just as mysterious as they are in humans...