offspring production, where sexual selection is focused on differential mating success. A 2006 article in the journal Science with her student Erol Akçay, and Meeko Oishi, formally presented the theory of social selection in terms of game theory. Beyond the Nash Competitive Equilibrium (NCE) imported to evolutionary biology by John Maynard Smith as the Evolutionary Stable Strategy, Roughgarden et al. discuss the Nash Bargaining Solution(NBS), which exists as an alternative to the NCE that is reached through negotiation. When playing in developmental time (as opposed to evolutionary time), a game player that stands to lose individual fitness at an NCE relative to its competitor may establish a threat point by promising to play a sub-optimal strategy. Through negotiation, for example via a side payment, the players can arrive at an NBS through playing mixed strategies across repeated games which thereby maximizes the fitness of the cooperative “team” (which consists of both players) rather than to any one player. Roughgarden et al. provide several examples of what such cooperative game play would look like in nature, and then define the evolutionary theory of social selection as one which considers such cooperative team games in the developmental tier as the primitive state, with sexual conflict as the derived state. They argue that social selection theory is mutually exclusive with the evolutionary theory of sexual selection, which treats sexual conflict as the primitive state and sexual cooperation as derived. Following the Science paper, forty scientists produced ten critical letters stating that the article was misleading, that it contained misunderstandings and misrepresentations, that sexual selection accounted for all the data presented and subsumed Roughgarden's theoretical analysis, and that sexual selection explained data that her theory could not. Troy Day stated that "many people felt that this was completely shoddy science and poor scholarship, all motivated by a personal agenda". Roughgarden stated she was "not altogether surprised" by the volume of dissent and that her theory was not an extension of sexual selection theory. Tim Clutton-Brock of Oxford University wrote a more detailed rebuttal in Science in 2007, in which he concedes the point that males can engage in sexual selection on females, even in species where the operational sex ratio is biased towards males, stating: “Consequently, satisfactory explanations of the evolution of sex differences requires an understanding of the operation of sexual slection in females as well as males”. Nevertheless, Clutton-Brock concludes that sexual