Actually, they have. The studies done for years point to stress on the pregnant mother causing a misproduction of her hormones. These hormones affect the fetus by causing the fetus' genes to "turn on" and turn off" the production of key proteins and fetus hormones at specific times. This imbalance apparently results in subtle changes to the fetus causing homosexuality.

There were also some prescription drugs that are suspected of causing hormone imbalances but the evidence is not as clear.

If the cause of homosexuality is caused by per-natal stress to the mother, the resulting child can hardly be found at fault for responding to preprogrammed hardwired tendencies unless those tendencies are combined with socially unacceptable behaviors such as child molestation.

There are several studies done over the years. Here is a recent one. The results really aren't "new".

"A new study suggests that homosexuality can be explained by biology, though not by genes specifically. Instead, the researchers propose that there are sex-specific epi-marks on the genes that are triggered during fetal development to maintain a hormone level balance. These switches cause fluctuations in DNA expression that impacts sexual development, including sexual identity and various other gender characteristics. These switches help protect both the fetus and the mother from the natural variation in sex hormone levels present during fetal development, which could help explain why homosexuality has evolved as a common variation of human identity."

http://thinkprogress.org/lgbt/2012/12/11/1318311/study-finds-biological-causes-for-homosexuality/#

If He is to be in this conversation, then you need to ask Him.
Otherwise, it seems, our opinions matter more.

I do believe, personally, that one day they
will find some kind of chromosome marker or
something that places a person on that pathway.

But nevertheless regardless if one is naturally more "attracted" to the same gender, that is not "homosexual". It only becomes "homosexual" when the two sleep together and that is what is being discussed. The actual conscious though of sleeping with the same gender. That is one's own choice to make such a thought/decision. REGARDLESS how they may be hormone wise or otherwise.

God couldn't care less if you find the same gender to be beautiful or attractive in one way or other. It is again when the conscious thought is put behind a physical action that we will be judged on.