In the journal Human Nature, the scientists suggested that the differences came about because of how human beings had evolved.
The researchers interviewed 530 men and women about their relationships and discovered 60% of 30-year-old women wanted sex "often" at the start of a relationship, but within four years this figure dropped to under 50%, and after 20 years it had fallen to about 20%.
But they found the proportion of men who wanted regular sex remained at between 60-80%.
The study also showed that tenderness was important for women and about 90% of women wanted this, regardless of how long they had been in a relationship. However, only 25% of men who had been in a relationship for 10 years said they were still looking for tenderness from their partner.
Dr Dietrich Klusmann, leader of the study and a psychologist from Hamburg-Eppendorf University, said he thought the differences were down to human evolution.
