Tomohiro Kono, from the Tokyo University of Agriculture (Japan), and colleagues have identified a gene, that although present in males and females, is active only in males. While the gene affords males to grow larger bodies, it may also compromise longevity.  The team assessed bi-maternal mice -- mice produced in a sperm-free manner, creating the animals with genetic material from two mothers and no father.  The resulting offspring, completely free of any genetic material inherited from a male, lived an average of one-third longer than mice with a normal genetic composition.  Further, the team found that the bi-maternal mice were significantly lighter and smaller at birth, with better performing immune systems.  The researchers identified these differences as a result of a gene, Rasgrf1, specific only to males via sperm. They conclude that: “These findings demonstrate that the maternal genome may play a role in ontogenetic longevity. Our results further suggested sex differences in longevity, originating at the genome level, implying that the sperm genome has a detrimental effect on longevity in mammals.”