The McBride-Bjornborgg Foundation of Sweden has concluded after a 16-month study that gay men's brains are "turned on" or 'excited' by other men's penises.

The study stokes the age-old controversy over whether homosexuality is a result of nature or nurture, whether it is inborn or a 'lifestyle choice'.

Lara Snordsen, a researcher on the study, said it showed that "gay men are 'chemically turned on' by the sight, taste, smell and feel of other men's penises".

She went on to say that "the study showed that the reaction was very similar to that of women.... provided those women aren't lesbians".