What books are the most scientifically and grounded in the possible reasons for the existence of "non-traditional" sexual orientation?

Chapters on non-traditional sexual orientation in the book "We are our brain" by Dick Swaab. The author is a neuroscientist who has researched this issue.

I can recommend Simon Lev's book Gay, Straight and the reason why.

amazon.com after all, it is designed for a more massive user (although in some places it is still replete with complex terms), but it contains all the knowledge gained in the field of studying homosexuality at that time (2010, but not much has changed since then) ... Levy describes the results of various studies by groups of scientists, geneticists, endocrinologists, neuroscientists, cognitive psychologists, ethologists, evolutionary and family psychologists. He describes them in such a way that they would be understandable to the average reader, in places in a very amusing form.

And although many details of the mechanism remain unclear, the overall picture in the book is described quite clearly: the formation of sexual orientation is a biological process which is triggered long before birth (a product of the interaction of genes, sex hormones and cells responsible for the formation of the body and brain).

Levy also writes that the study of homosexuality is not and should not be reduced to trying to find "what went wrong", or to invent a cure for homosexuality, or to get rid of the outdated amateur theory that homosexuality is the result poor parenting or early sexual experience. No. Modern scientists perceive sexual diversity as something valuable for humanity, and this diversity should be welcomed by society.

Unfortunately, the book has not been translated into Russian. But if you can watch TV shows or play games in the original (or with subtitles), then the language of the book will be understandable.