A scientific study has confirmed what some women have already known: that men shorten their lifespans simply by existing.

According to a new study from Stanford University School of Medicine, the male presence alone causes the release of certain signaling molecules that shorten women's lifespan.

For the study, reported in a press release, the researchers examined a laboratory roundworm, but their work could not pinpoint a definitive cause for a shortened lifespan. One suggestion was the stress of mating is enough to take years off the female's life. Another speculation is the male worms carried out a plan on the molecular level to rid themselves of their mates after the birth of their offspring.

"We've found that males induce the expression of a large number of genes involved in sensation and signaling in hermaphrodites," said study lead author Anne Brunet, PhD, associate professor of genetics. "This raises the possibility that the male-induced demise is not just due to the physical stress of copulation but instead involves some degree of active signaling. Indeed, we found that just placing hermaphrodites on plates where males had previously been present was sufficient to induce the premature demise of hermaphrodites."

The common laboratory roundworm is a mostly hermaphroditic species, meaning they have both male and female reproductive organs. Approximately 0.01 to 0.1 percent of the population are males. Despite the hermaphroditic worms being able to reproduce on their own, they are extra fertile with a male partner.

"In worms, once the male has mated and eggs are produced, the hermaphrodite mother can be discarded," Brunet said. "The C. elegans mother is not needed to care for the baby worms. Why should it be allowed to stay around and eat? Also, if she dies, no other male can get to her and thus introduce his genes into the gene pool."

Even worms incapable of birthing offspring were found to be subject to a male-induced demise. The researchers found the same evidence of heightened stress and shorter lifespans among the infertile worms who lived near males.

The next step for the researchers, as hinted by lead author Brunet, may be to examine the same effect in mammal species. The researchers work is published in the journal Science Express.

"The observation that this male-induced demise is present in several species of worms and has also been shown in flies suggests that it could have some adaptive benefits," Brunet said. "It will be interesting, of course, to determine whether males also affect the lifespan of females in other species, particularly mammals."