Evolutionary psychologist Satoshi Kanazawa has argued that an important cause of intergroup conflict may be the relative availability of women of reproductive age. He found that polygyny greatly increased the frequency of civil wars but not interstate wars. Gleditsch et al. did not find a relationship between ethnic groups with polygyny and increased frequency of civil wars but nations having legal polygamy may have more civil wars. They argued that misogyny is a better explanation than polygyny. They found that increased women's rights were associated with fewer civil wars and that legal polygamy had no effect after women's rights were controlled for.