Men with monotone voices are more attractive to women, a study has suggested.
Monotonous voices are associated with strength, power and confidence, researchers said.
The study at universities in California and Pennysylvania, US, found that men with a steady tone of voice had a significantly higher number of sexual partners than their more expressive counterparts, reports telegraph.co.uk.
Researchers measured the voices of male volunteers in various situations, including a simulated dating game and analysed the results.
The amount their vocal pitch changed - known as fundamental frequency variation - was found to be directly linked to the number of sexual partners the men had in the past year.
Experts believe that the monotone has evolved as an indication of authority and independence. They cited George Clooney and Clint Eastwood as examples of men who have monotone voice but are considered sexy.
David Puts, who led the research at Pennsylvania State University, said: "The power would be attractive, not the voice as such. It appears that the women are preferring males who are higher in status. It would be the status they would be most interested in."