Ben Jones at the University of Aberdeen in Scotland, and colleagues, showed 28 men and 28 women pairs of male faces and asked them to rate their attractiveness. The photos had been already been rated by 40 women as of about equal attractiveness.
The researchers then showed the same faces alongside a third photo of a female face in profile, positioned so she was looking at one of them, and smiling – or not. The viewers were asked to grade the faces again (see the picture here)
Women found the men who were being smiled at suddenly more attractive, while men were the opposite, they ... rated the men who were smiled at as less attractive.
Take a look at the photo and tell me what you think. FWIW I felt my eyes drawn over to the face on the left - the one who was 'being smiled at' - even though it is obvious the photo is a 'fake'. It was an automatic reflex. It is hard to be objective (given that I know the experiment) but I think I find him more attractive as well.
There is no mention in the article about whether the subjects were heterosexual or not. I assume so, from the context.
It would be interesting to fake up a similar experiment showing women being smiled at by men, and see what effect this has on how they are rated (my guess - both men and women would rate such faces as more attractive).
ETA My colleague says 'I prefer the one on the right - he doesn't look so grumpy' which might be another factor