Tropical climate produces more girls

Athens, United States, April 1: A new research shows that mothers living in tropical areas are more prone to having baby girls than those living in colder places.

Published in the Royal Society’s journal Biology Letters, the research has been carried out by Dr Kristen Navara, a U.S. researcher.

“Climate may change miscarriage rates and sperm quality. Or there may be some evolutionary advantage to having more girls than boys if you live by the equator,” she informs.

She conducted the study based on global birth data, collected by the CIA, of the sex ratios of 202 countries between 1997 and 2006. She also noted the socio-economic variations of these countries.

She found that the Central African Republic was the lone country globally to have maximum female births.

According to her findings, the countries falling on and near the equator produce more girls yearly than those located at temperate (51.1 percent) and subarctic (51.3 percent) latitudes.

“The results could indicate an adaptive strategy employed by humans, or there may be another non-adaptive strategy. Perhaps male ejaculate quality or miscarriage rates vary on a latitudinal scale,” she adds.

Studies done in the past showed that the chances of giving birth to a boy increase as one heads south of Europe. But it has always been difficult to draw conclusions about birth ratio looking at individual regions because of vast differences in their cultures, society, economy and many other factors.

Dr Bill James of University College London, who has spent his career studying sex ratio patterns, disagrees with the surmise of the present study. “Although the differences found were statistically significant, it was not as meaningful as other factors that have been linked to sex ratios at birth,” he says.

According to him, women who carry the hepatitis B virus and pre- eclampsia in pregnancy mostly have baby boys regardless of the climatic conditions that prevail in the area they live.

Dr Navara explains her findings thus, “The results shown here could indicate an adaptive strategy employed by humans, or there may be another non-adaptive explanation.”

She concludes that more research is needed to find the adaptive strategies to explain latitudinal variation in human natal sex ratios.