Let's talk first about parasites. Given the persistent influence that bacteria, viruses, and other parasites have had on human evolution (Van Blerkom, 2003), it's astonishing that so little scientific attention has been devoted to their impact on human psychology and hu-man culture. There are extensive bodies of research documenting the role of parasites on evolved patterns of animal cognition and behavior. Many studies reveal that mammals are sensitive to signs of parasitic infec-tion in potential mates and avoid mating with individu-als who show those signs (e.g., Kavaliers, Colwell, Braun, & Choleris, 2003). These kinds of effects are not restricted to mating contexts either. Bullfrog tad-poles selectively prefer to swim near healthy tadpoles, while avoiding tadpoles that carry parasitic infections (Kiesecker, Skelly, Beard, & Preisser, 1999). Closer to home (phylogenetically speaking), chimpanzees react with unusual violence toward other chimpanzees that show the physical symptoms of debilitating diseases (Goodall, 1986). It is likely that the human mind too is characterized by mechanisms designed to recognize and respond negatively to individuals who show signs of parasite infections—and to do so especially under conditions in which the risk of parasitic infection is es-pecially high (Kurzban & Leary, 2001; Schaller, Park, & Faulkner, 2003). In recent years, empirical studies have docu-mented the presence of just such mechanisms and their consequences on social cognition and behavior. Some of these consequences are straightforward: We stigmatize and avoid sick people, especially when we perceive their sickness to be contagious (Crandall & Moriarty, 1995). Additional consequences are more subtle. We not only stigmatize people who really are sick; we also stigmatize people who may be perfectly healthy but who—on the basis of some superficial feature—appear to pose a risk of parasite transmis-sion. And we do so especially under conditions in which we feel especially vulnerable to parasitic infec-tion. Xenophobic reactions to foreigners are stronger among folks who feel personally vulnerable to germs and disease (Faulkner, Schaller, Park, & Duncan, 2004). Individuals with deviant or nonprototypical morphological features—people who are disfigured or disabled, or who are grossly obese—are similarly stigmatized, and, again, this stigmatization seems to occur especially strongly among people who are per-sonally concerned about their own vulnerability to disease (Park, 2005; Park, Faulkner, & Schaller, 2003). The preference for physically attractive mates might also be understood within this context. Physi-cal unattractiveness is based substantially on per-ceived deviations from a population prototype (Langlois & Roggman, 1990). Consequently, the sub-jective assessment of unattractiveness may serve as a cue indicating the potential presence of a parasitic in-fection at the moment, as well as a cue indicating po-tential susceptibility to parasitic infections in the fu-ture. Within this conceptual context, it is no surprise that people care about the physical attractiveness of someone with whom they are destined to spend a lot of time with and that they care especially within pop-ulations that have historically been more vulnerable to debilitating parasitic infections (Gangestad & Buss, 1993). Now, in the results reported by Gangestad, Haselton, and Buss (this issue), we en-counter even more impressive evidence that para-site-prevalence influences mate-selection preferences, and this influence occurs across an even broader set of preferences.