man's many wives, a husband could afford to pay the bride price of a new wife and further his access to more land, meanwhile expanding his progeny. According to Boserup, in 1970, over much of the continent of Africa, tribal rules of land tenure were still in force. This implies that members of a tribe which commands a certain territory had a native right to take land under cultivation for food production, and in many cases, also for the cultivation of cash crops. Under this tenure system, an additional wife is an economic asset that helps the family to expand its production. The economist Michèle Tertilt concludes that countries that practice polygyny are less economically stable than those that practice monogamy. Polygynous countries usually have a higher fertility rate, fewer savings reserves, and a lower GDP. A 2014 study estimates that fertility would decrease by 40%, savings would increase by 70%, and GDP would increase by 170% if polygyny were banned. Monogamous societies present a surge in economic productivity because monogamous men are able to save and invest their resources due to having fewer children. Polygynous societies have a higher concentration of men investing into methods of mating with women, whereas monogamous men invest more into their families and other related institutions. Despite the expenses of polygynous marriages, a 1995 study suggests that men benefit from marrying multiple wives through the economic and social insurance that kinship ties produce. With a large network of in-laws, these men have the ties they need to compensate for other economic shortages. Libido Some analysts have posited that a high libido may be a factor in polygyny, although others have downplayed its significance. The sex drive as a factor in some Asian cultures was sometimes associated with wealthy men and those that were adjunct to an aristocracy, although such libidinal perceptions were at times discarded in favor of seeing polygyny as a factor of traditional life. For example, many sub-Saharan African societies view polygyny as essential to expand their progeny and kinship, a practice of high cultural importance. In this case, it would be hard to determine whether the origin was that of high libido, as polygyny would be practiced regardless. Other explanations postulate that polygyny is a tool used to ward off inclinations towards infidelity. In Edith Boserup's 1970 article on the study of Sub-Saharan African polygyny, higher incidences of adultery and prostitution