 Perhaps the most important analytical tool of the behavioral ecologist is the optimality model (Maynard Smith, 1978): however, frequency dependent models, which do not assume population fixation of a trait, such as evolutionary stable strategy models (Maynard Smith, 1982) (see also the entry on  evolutionary game theory)  and dynamic models, such those employed in studying life history traits (Roff, 1992), are also used. Optimality models are designed to show which of a set of possible variant behavioral strategies would maximize a local fitness  currency[2]  under a range of ecological conditions and constraints implicitly or explicitly represented in the mathematical structure of the model. These conditions are supposed to represent the selection conditions of the trait (the conditions responsible for driving its evolution by natural selection – Brandon, 1990); however, they are usually derived by observing the conditions under which the organism is currently living, since these are assumed generally to have remained much the same as the conditions under which the organism evolved (Turke, 1990). Werren (1980) provided just such a model for the jewel wasp above; the model suggests that the reason for the change in the ratio of sons to daughters when a female wasp finds an occupied pupa is due to the potential opportunity to mate with the daughters of the first wasp. If only the first wasp lays her eggs on the pupa, then the hatching daughters mate with their brothers and all their offspring are entirely descendants of the first wasp. This means the first wasp needs to produce very few sons—only enough to mate with all the females; the second generation reproductive success of the first wasp is maximized by maximizing the number of daughters. However, where there is a superparasitic wasp, the superparasitic wasp’s sons can mate with the large numbers of daughters of the first wasp. The superparasitic wasp needs to maximize the number of the females in the pupa that breed with her sons as opposed to their brothers, whilst at the same time limiting the amount of competition amongst her sons. So if she has only a few eggs to lay, it makes sense for her to lay almost all sons; as brood sizes grow larger, it makes sense to gradually increase the proportion of daughters in the mix. Werren calculated the optimal percentages of males and females for each brood size. His observations of male to female ratios fit the predictions of this model quite well but not perfectly.