The Immunocompetence Hypothesis was put foward by Folstad & Karter
(1992) and runs something like this... Testosterone places extra
strain on the immune system and makes it harder for the body to fight
infections; therefore in the days before modern medicine, or in other
species, a high level of testosterone should have resulted in death for
a male who didn't have a very strong immune system to start with.
We therefore theorise that if a male has physical characteristics
indicating high testosterone levels (such as looking more facially
masculine than average amongst humans, or in the case of Mandrills,
having more brightly coloured fur than other males), then he must also
have a good immune system, in order to tolerate the testosterone
without being very ill. Because good immunity is partly
heritable, the children of these 'immunocompetent' males should go on
to be healthier themselves, and survive better, which helps ensure the
survival of their mother's genes.
This is the extent to which a person is comfortable with sex outside a
monogamous relationship. The sociosexual orientation inventory
was first developed by Gangestad & Simpson and consist of 7
qestions asking about number of past one night stands, sexual partner
in the previous year, attitudes to sex and frequncy of 'extra-pair'
fantasies (i.e. fantasising about someone other than your partner).
Those who score highly are known as having unrestricted
sociosexuality and are more open to short term sexual encounters.
Those with a low score tend to be averse to sex outside a
committed relationship and are termed as having restricted