There have been studies showing brain differences between men and women, and there also have been studies that attempt to show differences in the brains of straight and gay people.
But, if you are born with a certain set of equipment, and it's workable, then you are genetically determined to be straight. Hence, it must be a learned behavior.
"But, if you are born with a certain set of equipment, and it's workable, then you are genetically determined to be straight. Hence, it must be a learned behavior."
However, there is no guarantee that chromosome count will automaticaly determine external sexual characteristics, gender identity or sexual orientation.
Take the case of women with androgen insensitivity syndrome (AIS). Externally, they are female and often quite attractive women. They are also attracted to men. A chromosome count will reveal they are XY, genetic male.
Furthermore, hormones and other drugs administered to the pregnant mother can affect brain development. If the hormone is administered at certain critical times during gestation, it can afect only brain development but not genital structure development.
Some elements of human behavior are most likely hard-wired into the brain during the gestational period.