A few years back a college instructor of mine told my class about a book set in the future in which some women get the ability to change into men and have relations with women fathering children and later they change back into women. I have been trying to find the title of this book for awhile.

Sounds kinky... Yet surprisingly not a Heinlein book.

I know there's a John Varley story that deals with that...."Options" I think. Probably others as well.

The Left Hand of Darkness?

There was a John Varley story about a woman having sex with a man who was herself. Who was a serial killer, but of only the woman. John Varley has his kinks.

That was my thought. If a college prof was recommending it, this would be a good guess. Classic SF.

I looked up info on The Left Hand of Darkness and I think that is the book my instructor talked about. Thanks for mentioning the title Nick Danger.