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It is often believed that women tend to live longer than their counterparts. But what has never been figured out is why this is so?

According to a study published Current Biology, genes are the reason why women outlive men.

A team of Monash University researchers have concluded that the mutations to the DNA of the mitochondria can account for differences in the life expectancy of males and females.

Mitochondria are vital for life because they convert our food into the energy that powers the body. In almost all species, the mitochondria DNA is passed down solely from mother to child, without input from dad.

Damian Dowling, Florencia Camus, and  David Clancy from Lancaster University used male and female fruit flies that carried mitochondria of different origins to uncover differences in longevity and biological .  They found that genetic variation across these mitochondria were reliable predictors of life expectancy in males, but not in females.

Dowling said the results point to numerous mutations within mitochondrial DNA that affect how long males live, and the speed at which they age.

"Intriguingly, these same mutations have no effects on patterns of ageing in females. They only affect males," Dowling said. "All animals possess mitochondria, and the tendency for females to outlive males is common to many different species. Our results therefore suggest that the mitochondrial mutations we have uncovered will generally cause faster male ageing across the animal kingdom."

The researchers said these mutations can be entirely attributed to a quirk in the way that mitochondrial genes are passed down from parents to offspring.

"While children receive copies of most of their genes from both their mothers and fathers, they only receive mitochondrial genes from their mothers. This means that evolution's quality control process, known as natural selection, only screens the quality of mitochondrial genes in mothers," Dowling said. "If a mitochondrial mutation occurs that harms fathers, but has no effect on mothers, this mutation will slip through the gaze of natural selection, unnoticed. Over thousands of generations, many such mutations have accumulated that harm only males, while leaving females unscathed."

The study builds on previous findings by Dowling and his team that investigated the consequences of maternal inheritance of mitochondria in causing male infertility.

"Together, our research shows that the mitochondria are hotspots for mutations affecting male health. What we seek to do now is investigate the genetic mechanisms that males might arm themselves with to nullify the effects of these harmful mutations and remain healthy," Dowling said.