Um... say what? Maybe I'm missing something, but "having a lot of biological older brothers" correlating with "being homosexual" does the opposite of suggesting that sexual orientation is "genetically" determined. After all, correct me if I'm wrong (in fact, I could be wrong) but it seems to me that your genes don't know how many older brothers you have. The number of older brothers you have is not something that is somehow encoded in your genes. So if your sexuality is affected by your # of brothers, that's an argument against it being "genetically" determined. More likely explanation would involve something like hormones (which your mother's womb affects) being affected by the older brothers (which your motehr's womb remembers) - this is not a "genetic"/DNA phenomenon, but a hormonal one. (Evolutionarily speaking, perhaps having many brothers tells your body you live in a male-rich village & have little chance of finding a mate yourself, thus don't "need to" be heterosexual, it's better to remove yourself from the competition thus increasing your brothers' (who have half your genes) chances of finding a mate... just guessing, but it's a far more likely guess than "it's genetic!".)
Writing a commentary piece that accompanied the study study, professors from Michigan State University said the research disproves the theory that sexuality is learned behaviour.
Whatever. I hate MSM writeups of science research. This research merely establishes a nonlearned component. That doesn't mean it's "not learned". Maybe having lots of brothers gives you that tendency AND any given person has to "learn" to indulge in that tendency? (With such "learning" being more likely for some people than others.) Both could be true.
After all, correct me if I'm wrong (in fact, I could be wrong) but it seems to me that your genes don't know how many older brothers you have. The number of older brothers you have is not something that is somehow encoded in your genes. So if your sexuality is affected by your # of brothers, that's an argument against it being "genetically" determined. More likely explanation would involve something like hormones (which your mother's womb affects) being affected by the older brothers (which your motehr's womb remembers) - this is not a "genetic"/DNA phenomenon, but a hormonal one.
Yes, it it were genetically pre-determined, the odds would be greater of multiple affected children and order of births would be irrelevant.