From what I've read, it seems that 1-2% of the population is gay - I assume these are the people "born this way". However I agree with you that there is an "environmental" component to homosexuality, where people choose to be in these relationships.
There was a study done by Roy Morgan in 2015 titled "Is Australia getting gayer" which shows a sharp increase in the past 10 years in teenagers and young adults identifying as gay (I think it peaks at around 6% for those in their 20s), but then strangely by age 50, you are back to the more normal figure of 1.7% of the population being gay.
I think the reason for the elevated figures in the younger ages, is environmental. As we normalise (or even celebrate) homosexual culture, the proportion of younger people identifying as gay, will I think, rise.
