Hmm. Ganske interessant artikel fra BBC her.
Researchers from Germany found that four years into a relationship, less than half of 30-year-old women wanted regular sex.
Conversely, the team found a man's libido remained the same regardless of how long he had been in a relationship.
Dr Dietrich Klusmann, lead author of the study and a psychologist from Hamburg-Eppendorf University, believed the differences were down to human evolution.