The proportion of males to females born is often slightly skewed in favor of males, according to the World Health Organization. While hypothetically, fertilized human eggs are about equally likely to have XX or XY chromosomes, many social, biological, and environmental factors potentially influence whether fertilization results in a live birth.
In a paper published in PLOS Computational Biology on December 2, a team of researchers report combing through data on 150 million people in the US over eight years, and data on 9 million Swedish people over 30 years, in an attempt to tease out the potential influence of some of these factors. They find significant statistical correlations between various environmental pollutants, as well as stressful events, and the sex ratio of babies born.
The team scanned datasets and recorded health statistics from the two countries, including information on the birth date, geographic distribution, and biological mothers of the ...
