226 RElS AND ZAIDEL
In every species, the central nervous system analyses health signals of
potential mates in order to ensure successful survival of the offspring through
the inheritance of disease-resistant genes. Elaborate adaptive strategies within
the animal kingdom to attract a potential mate have repeatedly been described
(e.g., Cronin, 1991; Gould & Gould, 1989). Consider, for example, the case of
the peacock and the peahen. The peacock, like many other birds, has evolved to
have a particularly long tail which, at first glance, does not appear to have any
functional purpose. In fact, the peacock’s tail represents secondary sexual
characteristics. As Darwin noted regarding many species of birds, spectacular
colours, feather modifications and displays have no use in foraging, flying, or
nest building (Cronin, 1991). The answer most likely lies in mate selection
strategies, as research by evolutionary biologists suggests that secondary sexual
characteristics are a reliable indicator of health quality (Moller & Nielsen, 1997;
Moller & Paola, 1998). Folstad and Karter (1992) and Wedekind (1992)
independently found that a link between parasite resistance and secondary
sexual characteristics exists because sex hormones, especially testosterone,
lower immunocompetence. When the peahen is courted, the size of the tail as
well as the colour and sheen of the potential mate’s feathers are judged. In other
words, the peahen is using secondary sexual characteristics to assess the
appearance of health of her potential mates (e.g., strong, healthy, agile, parasite-
resistant). So, even though the peacock’s tail does not enhance his ability to fly,
it does increase his chances of reproductive success (everything else being
equal). However, how the human brain assesses the display of health in faces is
poorly understood.
The foregoing is based on sexual selection notions which are anchored in
Darwinian evolution ideas. The concept of health appearance (i.e., how people
should look when they are healthy) versus real health in humans is difficult to
tease apart largely because of lack of empirical data. Consequently, the
correlation between real health signals displayed on the face and perceived
health is little understood. However, studies on the relationship between the
concept of health and attractiveness have been reported. Two separate studies
have found that tanned people were judged healthier than those who were pale
(Broadstock, Borland, & Gason, 1992; Miller, Ashton, McHoskey, & Gimbel,
1990). Another study investiged the relationship between facial attractiveness
and actual health in adolescents (Kalick, Zebrowitz, Langloes, & Johnson, 1998)
and found that ratings of adolescent facial attractiveness were not related to
adolescent actual health, whether during adolescence or later in life. Instead, the
study revealed a “halo effect”, that is, relatively more attractive faces were
rated as healthier. In another study in which subjects viewed photographs of
HIV-positive individuals, unattractive faces were judged more likely to have
acquired HIV through homosexual activity than attractive faces, and this was
particularly true for men’s faces (Boehm, Wambaugh, Riney, & Kunzelman,
1996). Together, the available findings suggest that when it comes to the facial