Scientists have discovered bisexual traits in men, where previous research found those claiming to be attracted to both sexes were, in fact, gay.

The findings, by Northwestern University, Illinois, were the result of a more in depth look at sexual attraction in men after a previous study failed to find any evidence of bisexuality in test subjects who identified as such.

The 2005 study had not claimed bisexuality did not exist, but that they had yet to find evidence for it: “with respect to sexual arousal and attraction, it remains to be shown.”

The study caused controversy at the time for the ease with which it could support the view that bisexuals are only homosexuals in the closet.

Released in the Biological Psychology journal this summer, the new research found “bisexual patterns of both subjective and genital arousal” in test subjects.

The selection criteria for the 2011 study was more stringent than before. Applicants needed to have had two sexual experiences with men and women, and one 3-month relationship with a member of each gender.

Many of the subjects who identified as bisexual exhibited signs of arousal to both men and women, compared with those in the previous study, who resembled gay men in their reactions.

Alan Rosenthal, a doctoral student of psychology and lead author of the second study said: “Someone who is bisexual might say, ‘Well, duh!'”

“But this will be validating to a lot of bisexual men who had heard about the earlier work and felt that scientists weren’t getting them.”

Jim Larsen of the advocacy group Bisexual Organizing Project told the New York Times: “It’s great that they’ve come out with affirmation that bisexuality exists.

“Having said that, they’re proving what we in the community already know. It’s insulting. I think it’s unfortunate that anyone doubts an individual who says, ‘This is what I am and who I am.'”