A new study shows that despite the aging population growing larger, women still outlive their male counterparts.

The research that looked at more than 1 million people, found longevity is at its peak compared to the last four centuries. Mortality rates in primates and apes were also looked at and found that humans are not the only ones enjoying a longer life.

Advances in medicine and public health strategies are the main reasons behind the longevity spike compared to many centuries ago when many were only expected to live until their 30s or 40s.

Despite this, males are still not as likely to outlive females and this was observed in primates as well as humans.

“In spite of the astonishing progress humans have made in lengthening the lifespan, a male disadvantage in lifespan measures has remained substantial — a result that will resonate with enduring public interest in male-female differences in many facets of life,” stated the researchers in the study.

Professor Susan Alberts, a Duke University biologist who lead the study with her colleagues, believes it’s down to genetics. With women carrying two X chromosomes and men only carrying one, any gene variants in their X chromosome that could potentially cause harm leaves men more susceptible than women.

“The male disadvantage has deep evolutionary roots,” Alberts said. “It’s puzzling, if we can make life last so long, why can’t we shrink the male-female gap?”

More research needs to be done in order to understand the gender gap and its connection to life expectancy and perhaps new interventions and scientific research can come up with a way to close the gap up in the future.

Details of the study were published in the journal Proceedings of the National Academy of Sciences.