wiki寫的

http://en.wikipedia.org/wiki/Homosexuality

The most common terms for homosexual people are lesbian for women and gay for men, though gay is also used to refer generally to homosexual men and women. The number of people who identify as gay or lesbian—and the proportion of people who have same-sex sexual experiences—are difficult for researchers to estimate reliably for a variety of reasons.[6] In the modern West, according to major studies, 2% to 13% of the population is homosexual or has had some form of same-sex sexual contact within his or her lifetime.[7][8][9][10][11][12][13][14][15][16][17] In a 2006 study 20% of respondents anonymously reported some homosexual feelings, although fewer participants identified themselves as homosexual.[18] Homosexual behavior is also widely observed in animals.[19][20][21][22][23]

當然不知道來源是什麼