What is the science behind being gay?

That if your a boy you like penis and if your a girl you like vajina there is no science behind it its just that you like someone of the same sex.

Actually there are two most important reasons where i research on it ,,, No 1 ,,, An environment where at home the majority of gals and once boy and he will automatically pose and act like girls and the behaviour of said boy will be like a girl and naturally he will think himself like a girl and if he is schooling where the majority of gals is much more then he will also adopt the nature of gals ,, and time to time his emotions will be like girls and in his growing age if he found some one other boy then he will feel his emotions like a girl,,, this is first reason,,, and second one reason ,,, that if some one gays which is already having some sexual with same his nature and if first time a boy cached by him and if he inter course with him some time and and he feel joy with it and then time to time he has been abused by some other gays and some one will discharge their sperms in his (0) hole then there will be surly germs can be raised and then he will feel some thing in his (0) hole and he will required a Duke for his/her (0) so that's why i am sure this is the main reason and science behind a gays persons,,, may be some other reason can effect that is depend upon the culture of different countries,,,