Nigeria's ambitious population policy, adopted in 1988, had its origins in the international population and development thinking of the time, set out in documents such as the World Population Plan of Action and the Kilimanjaro Programme of Action. The policy has had at most a modest effect in curbing the country's high fertility. This failure, it is argued, stems from the policy's implicit assumption of a single, monolithic cultural reality and its disregard of male reproductive motivation. Belief systems in Nigeria are extraordinarily diverse in detail but share a common interest in the fertility of crops, livestock, and people. Patterns of social organization are similarly varied. For an effective population policy, the government needs to find ways of incorporating distinct elements of the cultures of the different ethnic groups, leveraging rather than suppressing the country's cultural diversity.