Key evidence of sexual orientation: Pupil dilation

Results also revealed that bisexual men were attracted to both men and women, an idea that has been disputed, and that heterosexual women may be aroused by both genders, despite being straight…

“The female brain is not as differentiated,” said Sandra Witelson, a professor of psychiatry at the Michael G. DeGroote School of Medicine of McMaster University. “They don’t have as strong a response for only men, as heterosexual men have for only women.”

The female tendency to be aroused by both sexes may be because of female brain composition, Witelson said.