You can find a great analysis over at Congenial Times reporting GSS evidence for Cochran's "gay germ theory." According to the theory, homosexuality is caused by infections affecting brain development. The GSS data shows that a disproportionately high number of gay men are born in June. According to the analyst, if an embryo were conceived in September, he would be exposed during the crucial first trimester to the peak flu season, and would then be born in June.
The problem with this is that, according to the CDC, the peak month for flu for the past 26 years has been February (see the graph above). The peak conception month should be December since Mom and embryo are exposed to three bad months. Looking over a longer period, November through February would be the worst 4 months. The best four months for conception would probably be April through July since you are exposed to no months with a particular flu problem. Focusing on the month of birth instead of conception, the worst period should be August through November and the best, January through April.
I'm looking at 4-month periods because the GSS has a small number of homosexual respondents, and cell sizes increase as we merge them. We can also boost sample size by combining homosexuals and bisexuals (as Congenial Times did, N = 167).
Percent born between August and November (bad months)
Straight men 33.9
Gay and bisexual men 34.2
Percent born between January and April (good months)
Straight men 32.9
Gay and bisexual men 28.8
Gay and bisexual men are a bit less likely to be conceived during the low-risk months, but do not differ from straights during the flu season peak. The evidence here for the theory is weak.