In spite of its checkered intellectual history, and in spite of the myriad proposals ofalternative models that claim to account for the broad range of human behavior and todispense with the need for selection above the organism level, a multilevel selectionframework remains the only coherent...

Much of Africa has been ravaged by the AIDS epidemic. There, heterosexual contactis the primary mode of transmission for the HIV virus. Even when access to condomsis good and their price low, a large fraction of young Africans continue to engage inunprotected sex. In this paper, we propose a...