Gay, Straight, and the Reason Why: The Science of Sexual Orientation by Simon LeVay; rating: 8/10

Taking a systematic approach of a scientist, LeVay captures all the latest findings in the area of how human (and animal) sexual orientation comes to be. In the process there are a lot of interesting lines of reasoning covered, many discounted and a few very suggestive. LeVay himself jumped into the controversy many years ago with his study of the size of INAH3 in brains of gay males being the same size as women (smaller than straight males) [Of course leading to the question of how/why?].

I believe it can be said that much remains a mystery. But if I might try to write my own summary of the current state, it might be something like this: (1) genetic studies of identical and dizygotic ("fraternal") twins show that homosexuality might be around 30-50% genetically determined, and (2) a lot of studies point to hormones in the womb contributing possibly to homosexuality. LeVay also tries to uncover possible reasons for the genetics and why it may not be selected out of the genome.

There are some interesting little tidbits in the book, such as some studies have found that the torsos of gay men are longer relative to their legs. (Someone could do a larger, more definitive online survey of jean inseams versus height.)

I guess overall, I found the information interesting and useful. I do think that all the science is just background for the political questions which may mainly not hinge on the biological mechanism behind homosexuality and its existence. Many people do not believe in science and so whether or not it occurs as a byproduct of an evolutionary purpose has no bearing on their opposition to it.