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aberglas comments on Natural selection defeats the orthogonality thesis - Less Wrong
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One particular example of those "evolutionary accidents / coincidences", is homosexuality in males. Here are two studies claiming that homosexuality in males correlates with fecundity in female maternal relatives:
Ciani, Iemmola, Blecher: Genetic factors increase fecundity in female maternal relatives of bisexual men as in homosexuals.
Iemmola, Ciani: New evidence of genetic factors influencing sexual orientation in men: female fecundity increase in the maternal line.
So, appear to be some genetic factors that prevail, because they make women more fecund. Coincidentally, they also make men homosexual, which is both an obstacle to reproduction and survival (not only due to the homophobia of other's but also STDs. I presume, that especially our (human) genetic material is full of such coincidences, because the lack of them (i.e. the thesis that all genetic factors that prevail in evolutionary processes only lead to higher reproduction and survival rates and nothing else) seems very unlikely.
Considered correctly, your own stated facts about homosexuality show how homosexuality could exist in a world where all genetic evolution is designed to get more of the evolved genes into future generations than would otherwise be there. If a particular gene H makes women more fecund and men homosexual, then we would expect: 1) more women passing on gene H to their offspring then women without gene H 2) fewer men passing on gene H to their offspring then men without gene H.
Now which one of those effects "wins" is tricky and their are a number of genetic factors that could influence this. At 0th order for genetic purposes, women vary in their fecundity between each other much less than men do between each other. Genghis Khan and any high status male with 100s of concubines has 100s of times as many offspring as the median male, while the Queen of Egypt would still be limited to about once child every 2 years for about 30 years. Losing some men from the gene pool by giving them an H will not reduce the overall rate at which new humans are produced: there will be many heterosexual males volunteering to keep the females fertilized. But something that raises a female's output from 1 baby every 2 years to 1.1 babies every two years? That would seem to impart a big advantage to the people who had this extra bump in group fertility.
I'm not claiming I've done the math to show that such a gene does win for genetic fitness all things considered. But there are plenty of genes that are like this: the gene for sickle cell anemia: obviously getting sickle cell anemia is not pro survival for the individual who got a double dose of those genes, but the resistance imparted to the carrier of a single copy of the gene to Malaria, well that can pay off, and with enough malaria around, it can pay off more than enough to make up for the losses from the double-dose of the gene.
Makes sense.