New Study: Climate Plays a Greater Role Than Expected in Determining the Sex of Births

A recent scientific study revealed that rising temperatures and climate changes may directly affect the ratio of male to female births, potentially reshaping demographics in the long term.

Heat and Reproduction: Females More Present

The study conducted by the University of Oxford analyzed over 5 million births in 33 countries across sub-Saharan Africa and India, showing that warmer climates tend to increase the ratio of females compared to males, especially when temperatures exceed 20 degrees Celsius.
Dr. Yasmin Abdel Ghani, the research supervisor, stated that extreme heat is not just a health threat but a fundamental factor affecting embryo survival and family behavior in regulating reproduction, thus reflecting on the gender balance in societies.

Regional Differences in Effects

The study indicated that mechanisms vary by region: in sub-Saharan Africa, maternal heat stress leads to more male embryos dying before birth, while in India, effects are seen later in pregnancy, especially among older women who have not previously given birth to males.
The study also confirmed that the natural sex ratio is not globally equal, as typically 101–102 males are born for every 100 females, but this ratio can be affected by climate as well as social practices such as male preference and selective abortion.

Seasonal Effects on Male Fertility

In a separate study from the University of Manchester, over 15,000 samples from Denmark and Florida were analyzed, showing that sperm quality peaks in summer and declines in winter, even in regions with consistently warm climates, indicating that temperature alone does not explain all changes.

Professor Alan Beattie commented on the results, saying: "It is astonishing that these seasonal patterns recur in two completely different climates, opening the door for further studies to understand the complex relationship between environment and fertility."