Think of it this way - your friend needs to get to Location A by 2 pm. He is currently at Location B. You are at Location A. He arrives at 2 pm. Do you now have enough information to determine which ROUTE he took to get from A to B? You don't. You know the route you always take, but there are multiple ways to get from A to B.
There is a phenomenon in genetics called
pleiotropy:
Pleiotropy describes the genetic effect of a single gene on multiple phenotypic traits. The underlying mechanism is that the gene codes for a product that is, for example, used by various cells, or has a signaling function on various targets.
Homosexuality rewires portions of the brain. The sexual orientation of homosexuality resides in the brain. It's entirely expected that MORE than just sexual orientation is affected by whatever change has occurred. The roots of clinical depression in homosexuals need not be entirely the same as seen in heterosexuals. For Pete's sake the brains of homosexuals are wired differently.
Here's a real life example of
pleiotropy:
Belyaev chose the silver fox for his experiment; this species is related to the dog, but it is not domesticated. The initial foxes in Belyaev's experiment were not trained in any way, but simply tested for tameness at an early age. Starting at age one month, a human researcher would try to feed and pet the foxes, either alone or in the company of other foxes. The animals' responses varied from aggressive behaviors (such as biting), to indifference, to seeking interaction with the person more than with the other foxes. The tamest foxes were then selected for breeding the next generation, although fresh genes were supplied through continual outbreeding.
Belyaev and his colleagues did indeed create a population of foxes that differed in temperament and behavior from their wild cousins. The foxes changed physically as well, with alterations in coat color appearing as early as the eighth generation—typically a loss of pigment resulting in white patches. The foxes also developed floppy ears and curved tails, mirroring traits seen in dogs as well as other domesticated species (Figure 2).
One of Belyaev's hypotheses was therefore satisfied: Selecting for one trait (behavior) also changed other traits (here, aspects of the foxes' physical form).
Whatever is causing homosexuality results in behavior which is noticeably expressed with regards to sexual orientation and so we classify homosexuals by their most salient characteristic. We should be expecting other behavioral or physical changes to ride alongside the change in sexual orientation. Depression is a likely candidate due to its high incidence in the community and the fact that even drastic changes in the socially constructed environment of adult homosexuals which either remove or attenuate the situational stressors doesn't result in a drastic lowering of depression. Now what happens if we examine the extremist 100% environmental determinist position across time? Society has gone from actively condemning homosexual and publicly shaming homosexuals to teens now actively seeking out young homosexuals so that they can use them as props to signal their own heightened tolerance. Homosexuality is celebrated on TV, enlightened liberals love to make a show of attending Gay Pride parades, etc - it doesn't matter how much the stigma and the environment has changed over the years, what's important is that there has been a change. If the environment has changed then we should expect to see some movement in the rate of situational depression in the homosexual community. Something. What do we see?
Nothing.
Between 1970 and 2002 the suicide rate amongst homosexuals remained constant despite the changing cultural conditions. Situational depression is a reaction to conditions found in the patient's environment. If the environment improves, then depression is alleviated. Is anyone prepared to argue that the cultural conditions that homosexuals in 2002 face are identical to those experienced by homosexuals in 1970?