A fact-packed synthesis of an impossibly broad subject, but Ryan and Jethá manage to make some sense of it all. A well-researched book like this that challenges the "standard narrative" of human (and closely related primate) sexuality has been sorely needed. There are some great diagrams, too (e.g. the comparison of monogamous/promiscuous species and their genital and breast sizes).

As the LOC note by the publisher reads, "A controversial, idea-driven book that challenges everything you know about sex, marriage, family, and society." Despite this alleged controversy, the authors are careful not to prescribe too much. While there are a few too many sarcastic remarks, the humor is usually appropriate to the point that the authors are trying to make.