The way I heard it, in my college zoology class, is that eggs, whilst in the ovaries, are essentially male or female (filled with either primarily testosterone (male) or primarily estrogen (female)). If a "male" egg is surrounded by "female" eggs, some of the estrogen from the female eggs will leak into the male egg and cause it to have a higher than normal estrogen level. If this egg is one that ends up being fertilized, tada, a homosexual you have. Same thing goes for "female" eggs surrounded by "male" eggs, producing a lesbian. Also, pollution is known to contain chemicals which can cause egg cell layers to weaken, thus allowing for more leakage, which may mean homosexuality is becoming more common than in the past and will become more common in the future.
This is just a theory from what I understand and I may be remembering it incorrectly as I took the class 4 years ago, but that's the way I understand it.
This is just a theory from what I understand and I may be remembering it incorrectly as I took the class 4 years ago, but that's the way I understand it.
Think when they scan the brain the activity often shows something similar to the opposite sex, and not the gender they were born as. I think it's pretty silly to assume they're all born gay, I have NO doubt that some just chose it. I also think a lot are probally bisexual but might not know it, since being bisexual or at least curious/attracted to both sexes is pretty normal. It's mainly culture that has made us pretty homophobic, if this was ancient greece many of us would be great 'mates' 
Johnny B said:
Not true since ova are all the same and it is the sperm that determines sex.
Opinion is divided upon whether the orientation is genetically determined or is due to maternal factors whilst in utero or both interacting. Claims have been made for a gene conferring male homosexuality.
If this orientation is indeed genetically determined and since homosexuals produce fewer, if any, offspring then the orientation is genetically maladaptive and should decrease in successive generations. Since it is found at probably the same frequency in all cultures and throughout history then, if it is genetic, those who "carry" a "latent" predisposition (meaning in a similar way that females can carry the gene for haemophilia but are never affected) must be genetically more successful and have more offspring.
I also find it interesting that male homosexuals seem to be over-represented in certain fields, particularly various areas of the Arts. So it might seem that the behavioural orientation is in some way linked to some kind of artistic personality.
