For the most part, the nature vs. nurture debate is settled. Most people agree that it's a bit of both. However one area that this debate still rages on is under the topic of homosexuality. It has captured peoples' attention because of the political debates over whether or not homosexuality is a choice. This article from the Boston Globe looks at a set of identical twin boys. One of them is traditionally masculine and one of them is gay and feminine. The article is interesting because they are identical, but not both are gay, so it seems to not be genetic. Yet, on the other hand the gay child has been more feminine since before he could talk. These brothers however are just one case. The article does discuss other research that has been done, and all that research seems to point to the theory that homosexuality is at least partially genetic.
As I personally do believe homosexuality is genetic, I do not find these results surprising. Although to avoid confirmation bias I admit that no one has attempted to replicate (as far as I know) these studies. Yet, many different research methods have been employed, and all seem to be pointing towards the same thing. What is important to understand for the political debate is that whether homosexuality is eventually shown to be a product of nature, nurture, or both, 'nurture' should not be mistaken for 'choice'.