http://www.digitaljournal.com/article/271518

Study : More girls are born in Tropical climates than elsewhere

Posted Apr 25, 2009 by Michael Cosgrove
Couples who live in tropical countries are more likely to give birth to girls than those in, say, America or Europe. That is the outcome of a correlation study carried out at the University of Georgia by the endocrinologist Kristen Navara.
bath time
bath time
Chesi - Fotos CC's
The study, published in the British Biology Letters revue, consists of an analysis of CIA statistics concerning births in 202 countries between 1997 and 2006. The world average is 51.3 percent of boys (48.7 percent girls), but there are large differences depending on the geographical location of a given country.
It turns out that the figure for girls rises to 49.2 percent in Subsaharian Africa, and drops to a low of 48.5 percent in Europe. This kind of ratio, although small in pure percentage terms, is large in terms of its impact on birth rates over the long term, and is to be seen in all parts of the world.
In France for example, the rate is about 105 boys for 100 girls, whereas in China it is 120 boys for 100 girls.
Another interesting conclusion is that these figures remain the same even when cultural preferences, such as the preference for boys in India and China, where many abortions of female foetuses are carried out, are taken into account. The same thing happens in numerous African countries.
That is why Navara correlated the figures to climatic conditions.
She also gave biological explanations for the phenomena.
She says that wild animals, as well as laboratory animals, produce more spermatozoon's in summer than in winter. This is linked to the amount of light which they receive and is controlled by the pineal gland, situated in the brain. It plays a pivotal role in biological rhythm changes which result in changes in gamete production, which uses melatonin as the interface by which the gametes assimilate changes in light. This results in changes in male/female birth rate patterns.
This is why it is possible to obtain more males than females by subjecting animals to less light, and more females when lighting is left on longer.
And the same thing happens to human beings. The more light they receive, the more girls they give birth to.
(Source – Le Figaro)