Women are more likely to be bisexual than men, a study found.
The poll of more than 9,000 young adults showed that females were also more likely to choose the label "mostly heterosexual".
They were also more likely to change their mind about their sexuality.
In contrast, males tended to describe themselves as "100 per cent heterosexual" or "100 per cent homosexual".
Researcher Elizabeth McClintock said: "This indicates that women's sexuality may be more flexible and adaptive than men's".
Dr McClintock, of the University of Notre Dame in Indiana, analysed the results of a US study in which more than 5000 women and 4000 men were questioned on their sexuality three times, generally at the ages of 16, 22 and 28. Questions included whether they would describe themselves as "100 per cent heterosexual", "mostly heterosexual", "bisexual", "mostly homosexual" or "100 per cent homosexual".