This section is from the book "Human Sexuality", by J. Richardson Parke. Also available from Amazon: Human Sexuality.
It is unquestionable that the mind is capable of producing not only such, but even greater, effects upon the physical mechanism; but, on the other hand, those who find the beginnings of homosexual feeling in environment, defective education, and other psychologicaJ influences, will equally fail in satisfactorily accounting for every instance of its manifestation. A normally-minded male may be reared amid the most feminine surroundings, and associations, and yet preserve his sexual masculinity; while, if he be otherwise predisposed, through neuropathic or prenatal taint, no association with men will prevent his lapsing into inversion. It seems to me, in all amphibolous cases, in view of the etiological difficulty which confronts us when we attempt their classification, that what we may call the " instinctive test" ought to prove the most conclusive.
When a person feels, without any previous habitude, a psycho-sexual attraction toward an individual of the same sex—producing desire, and even orgasm, by pure psychical influence, and without artificial means—that person is homosexual by instinct, and no question of acquisition need be entertained.
But when a man or woman is seduced into, or performs homosexual acts without his, or her, own initiative, and without previous instinctive preferences for such acts, cultivated homosexuality may be inferred.
 
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