Roth and colleagues ruled out hydrogen sulfide’s influence on each of these pathways. Instead, they suspect it acts through a different mechanism. One theory is that exposure to H2S naturally regulates the activity of a gene called SIR-2.1, which has been shown to influence life span in many organisms, including the nematode. Previous studies have found that over-expression of this gene increases the longevity of C. elegans by 18 percent to 20 percent.