book on human sexuality evolution
Wild connection by Jennifer Verdolin is good, but it really depends on what you are looking for is there a specific area you are trying to learn about?

The Third chimpanzee might interest you, it compares human behavior to the other chimpanzee species, sex is only a small part but it it=s there. 

I a can warn you against a book I used ot like,sperm wars by Baker, A lot of the research is his own and there have been a lot of issues with people being unable to replicate many of them, so a lot of it untrustworthy which is a shame becasue I really liked his writing style.