New evidence suggests that Mother Nature has her own means of handling cheating wives. Researchers have found that a gene responsible for semen viscosity has evolved more rapidly in primate species with promiscuous females than in monogamous species. The changes may affect which male's sperm impregnates a female with multiple partners.
Previous studies had shown that when a species has a high rate of polyandry—the mating of one female with more than one male—a variety of adaptations have evolved that increase the odds that an individual male's sperm meets up with an egg. For example, compared with males in monogamous species, those from many polyandrous species have larger testes capable of producing and storing more semen, and their sperm contain more mitochondria, the energy-producing organelles that power sperm's motility.