Illustration: Cathy Wilcox    Professor Leigh Simmons, of the
University of Western Australia, said having a diverse set of
genes was beneficial because it meant a person had more defences
against invading germs. Such genetic ''success'' was thought to
influence mate choice, he said.  When looking for a partner,
people are subconsciously seeking out someone with different
genes from their own to create offspring with a lot of genetic
diversity, said Professor Simmons.  He said that a specific
group of genes called the major histocompatibility complex
(MHC), a driver of the immune system, had previously been shown
to influence mate choice.  To test if this genetic diversity
affected the number of sexual partners a person had, Professor
Simmons and his colleagues assessed the genetic variability of
74 females and had them fill in a questionnaire about their sex
life.  After removing the bias associated with age and sexual
attitudes, Professor Simmons found those women who had more
genetic diversity in their MHC