Environmental Influences, Domain Specificity, and Heterozygous Potential:

Environmental influences have also contributed profoundly to human sexual behavior, which becomes particularly evident when one examines certain statistical tendencies pertaining to both conscious and unconscious choices in female mate selection (Gerrig & Zimbardo 2005). As is the case with many sexually reproducing organisms, human females have evolved a marked preference for both physical and behavioral male traits consistent with the ability to provide physical protection and to garner both natural and social resources. Females of many species prefer male suitors who display characteristics such as large relative body size, robustness, good health, and those suggesting physical strength, aggressiveness, and leadership (Margulis & Sagan 1999).

Whereas some of those traits are observable externally (such as relative size), others are imperceptible on any conscious level. This is particularly true as regards heterozygous potential conducive to healthy offspring, such as the marked unconscious preference demonstrated by human females in experiments designed to investigate the relevance of male scent pheromones on female mate selection. Roberts (et al. 2004) demonstrated the connection between male facial symmetry and female preference that corroborated earlier series of studies that identified the link between female scent preferences and relative compatibility with heterozygous elements of human resistance to disease as a function of genetically determined major histocompatibility complex (MHC) gene code variation. Those studies determined that human females exhibit a specific preference for the scent of males whose MHC genes are sufficiently different from their own to confer maximum benefit in the strength of the immune system of their progeny.

Furthermore, these preferences change at different points of the menstrual cycle: ovulating females prefer scents corresponding to different MHC genes, whereas during the time that they are unfertile or pregnant, they strongly prefer the scent corresponding to similar MHC genes. The researchers theorized that this adaptation relates to the need for optimal genetic matching in mate selection...

(Modern changes in human society have changed some of the overtly obvious criteria valued by females, such as the greater emphasis on earning potential and financial success that, in contemporary society, often become more important to the health and welfare of their children than relative physical size and strength Margulis & Sagan 1999). Finally, this dynamic actually provides one of the most fascinating elements of the interplay between evolved sexual preferences and modern environmental influences. Females of many other primates often supplement the genes of their long- term partners with those of other males through short-term clandestine sexual encounter
Whereas human females maintain no conscious desire to become pregnant in illicit affairs, they are statistically more likely to engage in extramarital sex precisely when they are most fertile. Furthermore, their choices for short-term affairs are also more likely to emphasize the superficial physical traits whose evolutionary value in long-term mates has been reduced in contemporary human society (Barash 2001).