You spot a hot stud from across the room, give him The Look and gaze deeply into his eyes while fantasies of all the fun you are about to have run through your head until you bigger head ponders the all important question: Is he gay? They say the eyes are the mirror of the soul. Cool. But it’s not usually his soul you’re thinking about. The age old question of is he or isn’t he – or will he at least for the night – has to be settled by your finely tuned sense of gaydar in most cases. Surely the gods provided some better way of determining if the hottie you just decided to spend the rest of your life with will be willing to move to a state where gay marriage is legal. Fear not, the latest word is that there is a way to tell. It’s all in how large one part of his body grows.

And yup, it smells like science to me.

In a recent study published in the journal PLoS ONE by researcher Ritch Savin-Williams, a developmental psychologist at Cornell University, it was found that participants responded to pictures of those they were attracted to with a dilation of their pupils. Of course this isn’t exactly news, “My what big eye you have!” was how Little Red Riding Hood responded to sensing the Big Bad Wolf’s interest . But it is nice to hear when science is willing to back up fairy tales.

Savin-Williams and his colleague Gerulf Rieger recruited 165 men and 160 women, including gay, straight and bisexual participants, to watch separate one-minute videos of a man masturbating, a woman masturbating and neutral landscape scenes. The videos were all matched for brightness so that differences in light wouldn’t skew the results. Using a gaze-tracking camera to record participant’s pupils the researchers found that when people look at erotic images that arouse them, their pupils open up in an unconscious reaction.

The results showed that pupil dilation matches the subject’s sexual preference: Straight men respond to sexual images of women, and gay men respond to sexual images of men. Bisexual men respond to both men and women. “This new study is first large-scale experiment to show that pupil dilation matches what people report feeling turned on by,” said Savin-Williams. “If a man is straight, his eyes are dilating towards women, and the opposite with gay men, their eyes are dilating to men.”

The dilation is a sign that the autonomic nervous system — the system that controls involuntary actions like pulse and breathing — is ramping up. Interestingly, the study found women’s pupil’s dilate over erotic stimuli regardless of the gender. The researchers said this does not mean all women are bisexual, and instead floated the theory that this is because women have been at risk of being raped throughout history, and have evolved to respond with lubrication to any sexual stimulus, no matter how unappealing. Something tells me Savin-Williams is gonna have a hard time getting a date from now on.

So next time you are out clubbing and want to know if that hottie is willing to share your bed, gaze deeply into his eyes. If his pupils dilate, you might just be in luck. Or it could just mean the E finally kicked in.

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