¿Por qué algunas personas son gay?

THE SCIENCE OF SEXUAL ORIENTATION

From as recent as the 1980s there was a belief that people were born with no sexual preference and that life experiences are the determinate factor that leads to a particular sexual orientation. Sexual orientation cannot be changed by social influences or surgery. Studies emerged in the late 1990s that indicated that influences from hormones impacted sexual orientation during pregnancy.
All human characteristics have a normal variation. Whether we are looking at height, weight, eye color, or sexual orientation, normal variations occur for all traits.

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SCIENCE OF SEXUAL ORIENTATION
NATURE VS. NURTURE
GENETICS AND ORIENTATION
PRENATAL DETERMINATION