Not to 'spam', but from another thread and recent post;
Try this for consideration;
Nature's preference is towards the reproductive half of a bi-sexual species, i.e. the female. So, in the case of mammals (and some other fauna) the eggs of a female always contain an "X" chromosome which blueprints to make a female of the species.
The male sperm might contain and "X" chromosome and reinforce the making of a female, or a "Y" chromosome which sets the stage for altering the basic female pattern into the "mutant" male deviations.
However, for the transformation from female to male to go perfect, depends upon enough male hormone, testosterone during both the pregnancy (when genitalia and brain structure happens) and during puberty when the hypothalamus, which triggers sexual attraction, needs to be 'flipped' from basic female attraction to a male into the altered/mutated status of being attracted to a female.
If the matrix of genes and hormones are not sufficient to make the needed development/transitions both in the womb(fetus) and during puberty/adolescences, than there may be sexual orientation/attraction "confusion".
I'm running the thumbnail outline here, in the above; but all is much better explained in this rather slim volume which covered about a hundred years of research in gender differences among mammals, including humans. The "explanation" for homosexual orientation is more implied than outright stated, FWIW;
Brain Sex: The Real Difference Between Men and Women Paperback – August 1, 1992
...
See also;
Brain Sex - Goodreads | Meet your next favorite book
and
BRAIN SEX | Kirkus Reviews
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The book points out the many differences between genders, some as mentioned above.