...but you had to ask! ;-)
The answer is both.
Both biological predisposition exists but the practicioners of same-sex acts do so by choice.
You're still (relatively) a newbie and so are not yet aware of the controversy that surrounds my views. Nothing upsets the HZ applecart so much as suggesting folks have a choice in their sexual actions.
I believe in reincarnation, and I believe that everyone has a percentage of the opposite sex as a result of lifetimes lived in an opposing gender.
I classify such as (+ -) polarity relationships.
Two gay men are usually female polarities, one possessing a stronger bias (as the result of more lives lived as a woman) and two lesbians are usually male polarities, also with one being more dominantly male.
Even the most heterosexual male/female will still possess 10-15% of the opposite sex within them. This becomes a serious problem when they find themselves in the body of the opposing gender.
How well does a 90/10 biased female behave when incarnated in a male body? Or a 90/10 biased male in a female body? Naturally they will be drawn to their same sex.
However, acting on these impulses (the choice part of the equation) will create a long-term problem. In future lives they will develop this reverse gender expression and when they return to the gender they are dominant experience-wise, they will now have this added same-gender sexual cycles in their experience quotient.
The universe balances things out. It is far easier for someone to remain heterosexual regardless of the gender they incarnate in when they are balanced better - who possess somewhere around a 40/60 gender bias. They will understand the opposite sex better and will make better mates.
Naturally, this is controversial. I had written a story about this issue which addresses the way gender bias will likely be treated in the future, when reincarnation is scientifically understood. It helps to see my views on the matter:
Eleshiana's Tale
It was early morning and the orderlies guided me in to see my new baby. Her mother was doing fine and the delivery went flawlessly. Ever since the vortical pulses sent by the nervous system during contractions had been identified in 2174, artificial contraction machines had been developed to deliver babies without much fuss. The doctors had set the optimal contraction and duration schedule for my wife and the baby's size and in twenty minutes Eleshiana had entered the world. The recorded time: 16 May 2419 05:45.
Now came the time all new parents are both anticipate and fear simultaneously - the FFIP. The FFIP (Fundamental Frequency Identification Process) chamber was impressive. A large holovideo terminal was in the center of the room and next to it was a contoured cradle-like chamber where the baby was placed. Eleshiana did not cry and seemed unfussy, I was hoping for the best, while my wife would be holophoned the results to her recovery room on a live feed. After social security collapsed and was abolished in 2035 advances had been made in brain wave identification. By 2053 the first reliable FFI was made available to hospitals and was employed by most of the world's goverments as a means of determining and recording personal identification. Yet it has come a long way since the early simple numerical designations. Now a child's brain is scanned and the FF identified. The first step is a comparison with all previous matches to that signal - and the gender bias is quickly ascertained. I look at the holoterminal as the names are displayed and added to one after the other:
Jennifer Rayla Davidson Born AD 2087 Passage 2190
Maybella Cynthia Nordermann Born AD 2197 Passage 2279
Thomm Jason Nordermann Born AD 2288 Passage 2395
_____________________________________________________
Eleshiana Laurie Miller FFID # 2,457,890,035,852.5402 CPS
Gender Polarity Recorded: Female 66.66%
_____________________________________________________
Seeing the same name was quite common during FFIP. Eleshiana was her own great grandson. Now came the interesting part as three faces appeared on the holoterminal. All of them look familar to me. Their life records were scanned for criminal activity and any criminal record. I was relieved to find she had been a stalwart citizen and had never even been arrested or charged with a crime. Various recorded holograms from the various lives were playing and it was overwhelming to see the pasts of our newborn. Again this total sense of familiarity. Eleshiana certainly made for a very attractive woman and a handsome man. The eyes and the lips and the nose were all very similar whether she was male or female.
One of the FFIP officials comes over to me and asks me if we desired a complete scan. My wife and I had debated the pros and cons but we decided it would be in Eleshiana's best interests if we knew her worst and best attributes. I gave my verbal consent and Trishaa gave hers over the holophone both were recorded and the procedure continued. The FFIP machines can pull out the strongest imbalanced signals and extract the data from them even though the lives covered had not yet been recorded by society.
Suddenly flashes of horrible violence appeared on the holo terminal. All passing at incredible speeds. Gunshots, knives, explosions, falling -all as seen and recorded from Eleshiana's perspective out of long gone eyes. All the old centuries seemed to be represented. So much pain! So much fear and suffering! I heard Trishaa burst into tears from her recovery room and I was stifling a sob myself when I saw her fade out under water, drowning. I couldn't contain my sobs either.
Oh, it was horrible.
Horrible!
The computer was tallying the various imbalanced waveforms and presented her statistics unemotionally:
FFID # 2,457,890,035,852.5402 CPS
Types of Violent Deaths Experienced:
12 stabbings
4 gunshots
8 falls
2 explosions
4 crushings
7 drownings
1 decapitation
5 burnings
I felt sick to my stomach. Meanwhile Trishaa continued sobbing in the recovery room over the suffering our newborn had already experienced. We would be more diligent. I made a vow to myself then and there not to let any of those things happen to her again - and to help her iron out those imbalanced wave forms so she would no longer be in such danger of repeating the incidents. The specifics were being printed on a report almost instantaneously. The FFIP personnel were legally bound to confidentiality and they wore the hardened, yet compassionate faces of folks who had literally seen it all. I had worked in the healing/therapy center for just 2 months but under recommendation and mutual agreement I had departed. Those who work with FFI devices in the therapy wards burn out quickly and few stay in the job for more than 6 months at a time.
When Trishaa and I had returned to our home with little Eleshiana we pored through the various details and suggestions contained in the report. While the civil computers recorded a 66.66 female polarity ratio - the detailed report from identified signals placed the number lower than we would have liked - 57.35% female and had identified a sizable number of rp (reverse polarity) lifetimes in which she had acted on her natural impulses. The report had made clear that she would likely experience mixed signals and attractions and it would be in her best interest to locate previous loves and relationships who were currently incarnated as males. These past attractions would create a normal union and increase the strength of her polarity bias. Trishaa had always been opposed to such government assisted matchmaking and told me there was no way she would try to find anyone. When I married Trishaa, I knew she was a bit old-fashioned and it had been me who had pushed this FFIP full scan. I had seen so much in the two months at the therapy center and I knew that parents who choose the full scan have a much better chance of helping their children balance their various pasts. I let Trishaa rest with Eleshiana as I went to the den and looked further through the complete report. I had separated the part that I didn't want Trishaa to see until after I had read it:
Current Parental relationships with:
FFID # 2,457,890,035,852.5402 CPS
This was the part which identified any clear relationships we had previously with Eleshiana.
FFID # 2,723,775,150,611.9001 CPS Current Father:
Brother 1
Husband 1
Son 1
FFID # 2,161,405,950,273.4210 CPS Current Mother:
Grandmother 1
Sister 1
Wife 1
I knew that the therapy center would tell Trishaa it was her past life as Eleshiana's wife that made her unwilling to try and find a suitable male for her. Likewise they would tell me that as her past husband she might have a very strong father-daughter bond and that I might be holding back her best interests by not seeking out someone from her pasts that has already come in or will come in. So I put in a request to monitor the incoming births. Trishaa will hate me, but I know that they are right. I doled out the exact same advice dozens of times to parents in similar situations. I fill out the request form and send it to the FFIP central processing. I put the report on my desk and I kiss little Eleshiana on her forehead. Trishaa is asleep as well and I give her a light and tender kiss on her lips, careful not to wake her up.
We'll make this lifetime one of the best ones - of that I can promise them.
That story explains a whole lot of relationship issues many folks have with their family. However, I have found, it is rather unpopular to suggest that same-sex relations are unhealthy or unproductive.
Now, I'm going to have to go back into hiding before the mobs come with the tar and feathers.

;-)
