Many politicians, business leaders, and scholars discount the role of public policy and emphasize the role of the labor market when explaining employers' maternity-leave policies, arguing that prior to the passage of the Family and Medical Leave Act (FMLA) of 1993, employers were already providing maternity leave in response to the increase in the number of women workers. Employers did create maternity-leave programs in the 1970's and 1980's, but not as a purely voluntary response in the absence of any government mandate. In 1972, the Equal Employment Opportunity Commission (EEOC) ruled that employers who allowed leaves for disabling medical conditions must also allow them for maternity and that failure to do so would constitute sex discrimination under the Civil Rights Act of 1964. As early as 1973, a survey found that 58 percent of large employers had responded with new maternity-leave policies. Because the 1972 EEOC ruling was contested in court, the ruling won press attention that popularized maternity-leave policies. Yet perhaps because the Supreme Court later struck down the ruling, politicians and scholars have failed to recognize its effects, assuming that employers adopted maternity-leave policies in response to the growing feminization of the workforce.

    Carotenoids, a family of natural pigments, form an important art of the colorful signals used by many animals. Animals acquire carotenoids either directly (from the plants and algae that produce them) or indirectly (by eating insects) and store them in a variety of tissues. Studies of several animal species have shown that when choosing mates, females prefer males with brighter carotenoid-based coloration. Owens and Olson hypothesize that the presence of carotenoids, as signaled by coloration, would be meaningful in the context of mate selection if carotenoids were either rare or required for health. The conventional view is that carotenoids are meaningful because they are rare: healthier males can forage for more of the pigments than can their inferior counterparts. Although this may be true, there is growing evidence that carotenoids are meaningful also because they are required: they are used by the immune system and for detoxification processes that are important for maintaining health. It may be that males can use scarce carotenoids either for immune defense and detoxification or for attracting females. Males that are more susceptible to disease and parasites will have to use their carotenoids to boost their immune systems, whereas males that are genetically resistant will use fewer carotenoids for fighting disease and will advertise this by using the pigments for flashy display instead.