Up to 70% of Amazonian cultures may have believed in the principle of multiple paternity

In these cultures, if the mother had sexual relations with multiple men, people believed that each of the men was, in part, the child's biological father. It was socially acceptable for children to have multiple fathers, and secondary fathers often contributed to their children's upbringing. Sexual promiscuity was normal and acceptable in many traditional South American societies. Married couples typically lived with the wife's family, which increased their sexual freedom. In some Amazonian cultures, it was bad manners for a husband to be jealous of his wife's extramarital partners. It was also considered strange if you did not have multiple sexual partners. Cousins were often preferred partners, so it was especially rude to shun their advances. Women believed that by having multiple sexual partners they gained the benefit of larger gene pools for their children. Women benefited from the system because secondary fathers gave gifts and helped support the child, which has been shown to increase child survival rates. In addition, brutal warfare was common in ancient Amazonia, and should the mother become a widow, her child would still have a father figure.