You mention that the “prenatal wash” plays an important factor and that this is partly determined by birth order and/or gender of prior births. However, what other factors determine the composition of the prenatal wash? Could it be the genes of the mother?
Also, how does the prenatal wash theory explain the quote I mentioned above, namely:
Maybe the prenatal wash in this family resulted in a higher percent of gays, but why?
If we don’t know all the causes of differences in the prenatal wash, we have just pushed the problem of why someone is born gay to why the prenatal wash was such that it resulted in a gay person. This is a little bit of progress, but more needs to be known to dismiss genetic influence on the composition of the prenatal wash.