Everywhere in the world women live longer than men - but this was not always the case. The available data from rich countries shows that women didn't live longer than men in the 19th century. What's the reason women have a longer life span than men? And how is this difference growing as time passes? The evidence is limited and we only have incomplete solutions. While we are aware that there are biological, behavioral, and environmental factors that play an integral role in women's longevity more than men, we do not know how much each factor contributes.