By Margarita Nahapetyan
Couples who live in the tropics are more likely to produce baby girls, compared to the couples who live in cooler climates, according to the Greek researchers who claim that there is a link between latitude and the gender of babies.
Dr. Kristen Navara of the University of Georgia in Athens, analyzed the sex ratio of newborn boys to girls in 202 countries, from northern Europe to equatorial Africa. The data was obtained from the U.S. Central Intelligence Agency (CIA) World Factbook. The scientists took into consideration socio-economic differences between nations and continents. The study which lasted for a period of 10 years, between 1996 and 2006, found a clear link between latitude and a skewed sex ratio - the closer is the mother's location to the equator, the more is the probability that she will give birth to a baby girl rather than a baby boy. Conversely, the higher the latitude - and the further she lives from the equator - the greater are her chances to deliver a baby boy.
The results revealed that, in opposite to existing figures, the ratio of boys born in tropical latitudes dropped to 51.1 per cent, compared to 51.3 per cent of newborn males in cooler climates. Tropical regions are the warmest, there is the least variation in the length of a day within the whole year, and throughout human history and evolution there have been relatively high levels of food and other resources.
The experts said that although the difference at first glance may seem very small, however, statistically, it is very significant and translates into large numbers of babies. And the difference was even larger between some of the countries in the research. For example, in tropical Central African Republic, the gender ratio was 49 per cent for baby boys, whereas in more temperate China the pro-male bias was 52.8 per cent, and in India - 51.2 per cent, Dr. Navaro said. "We found that this difference was independent of other cultural variables, including socio-economic status. It was an over-arching pattern and this effect remained despite enormous cultural variations between the countries we looked at," she said.
Other tropical countries with low male birth ratios included Grenada, with 50.2 per cent, Mauritius, with 50.3 per cent, Liberia, with 50.7 per cent and the Bahamas, with 50.5 per cent. These compared, for instance, with plenty of newborn boys in Asian countries, such as South Korea, with 52.6 per cent, and Armenia, with 52.2 per cent. Out of the ten countries that produce the lowest sex ratios, only three are from Africa, leaving seven which have never been known to practice sex-selective abortion. Indeed, it is a hard thing to explain, Navara said.
The results of another study, that had been conducted in Italy, showed that there is more chance for couples to conceive a boy in autumn, while those who long for a baby girl should try to conceive a child in spring. It is believed there that nature favors conception of boys from September to November and girls from March to May. One explanation of that might be the evolutionary need of keeping the overall sex ratio close to the 50:50 standard. Another could be associated with seasonal variations in the availability of food.
However, the study does not suggest that simply traveling to or spending a vacation in a tropical country, could increase a woman's chances to conceive a baby girl. The information used by the scientists in the research only applied to women who were born in the countries with warm climates.
The findings are published in the latest issue of the journal Biology Letters.