Thus, the dominant males have more frequent mating opportunities and the first-mate advantage. The first-mate advantage theory is speculated to occur in ring-tailed lemurs because after copulation some of the male's sperm hardens inside the female's vagina to form a copulation plug. Copulation plugs prevent subsequent mate's sperm from fertilizing the egg, thereby enhancing the first mate's chances of paternity (Sauther 1991). Their mating system is also classified as promiscuity because females mate with more than one male.