Warm weather produces girls

Experts have long known that boys’ and girls’ birth rates vary around the world, maybe in part because the female fetus is less fragile than the male—at times of stress, including war, the female birth rate goes up, reports the BBC. Now, new research suggests people living in hot climates have more girls than those living in more temperate parts of the world. While 51.5 per cent of babies born around the world are male, Dr. Kristen Navara of the University of Georgia found that, in countries closer to the Equator, far fewer boys were born annually than at temperate and subarctic latitudes: 51.1 and 51.3 per cent, respectively, despite "enormous continental variation in lifestyle and socio-economic status." She suggests the hot weather or long days could affect miscarriage rates and sperm quality, or that there may be an evolutionary advantage to having more girls for those who live in warm climates.

BBC News