The day homosexuality is proven, beyond any reasonable doubt, to be a natural phenomenon, I'll change my views on it.
NJ, it's been shown repeatedly that the chance of a male child being gay is increased by the number of older male siblings from the same mother.
The studies show that this is independant of whether or not the child was raised in the same house with the siblings.
The leading hypothesis is that it's caused by the mother's reaction to the repeat exposure to testosterone.
The fact that younger male siblings (even those given up for adoption and raised as only children) have a greater chance of growning up to be gay, indicates that what they've been telling us all along is in fact correct. They were born gay.
I assume this means you'll now be changing your tune.